Provided by: valgrind_3.21.0-0ubuntu1_amd64 
NAME
valgrind - a suite of tools for debugging and profiling programs
SYNOPSIS
valgrind [valgrind-options] [your-program] [your-program-options]
DESCRIPTION
Valgrind is a flexible program for debugging and profiling Linux executables. It consists
of a core, which provides a synthetic CPU in software, and a series of debugging and
profiling tools. The architecture is modular, so that new tools can be created easily and
without disturbing the existing structure.
Some of the options described below work with all Valgrind tools, and some only work with
a few or one. The section MEMCHECK OPTIONS and those below it describe tool-specific
options.
This manual page covers only basic usage and options. For more comprehensive information,
please see the HTML documentation on your system:
$INSTALL/share/doc/valgrind/html/index.html, or online:
http://www.valgrind.org/docs/manual/index.html.
TOOL SELECTION OPTIONS
The single most important option.
--tool=<toolname> [default: memcheck]
Run the Valgrind tool called toolname, e.g. memcheck, cachegrind, callgrind, helgrind,
drd, massif, dhat, lackey, none, exp-bbv, etc.
BASIC OPTIONS
These options work with all tools.
-h --help
Show help for all options, both for the core and for the selected tool. If the option
is repeated it is equivalent to giving --help-debug.
--help-debug
Same as --help, but also lists debugging options which usually are only of use to
Valgrind's developers.
--version
Show the version number of the Valgrind core. Tools can have their own version
numbers. There is a scheme in place to ensure that tools only execute when the core
version is one they are known to work with. This was done to minimise the chances of
strange problems arising from tool-vs-core version incompatibilities.
-q, --quiet
Run silently, and only print error messages. Useful if you are running regression
tests or have some other automated test machinery.
-v, --verbose
Be more verbose. Gives extra information on various aspects of your program, such as:
the shared objects loaded, the suppressions used, the progress of the instrumentation
and execution engines, and warnings about unusual behaviour. Repeating the option
increases the verbosity level.
--trace-children=<yes|no> [default: no]
When enabled, Valgrind will trace into sub-processes initiated via the exec system
call. This is necessary for multi-process programs.
Note that Valgrind does trace into the child of a fork (it would be difficult not to,
since fork makes an identical copy of a process), so this option is arguably badly
named. However, most children of fork calls immediately call exec anyway.
--trace-children-skip=patt1,patt2,...
This option only has an effect when --trace-children=yes is specified. It allows for
some children to be skipped. The option takes a comma separated list of patterns for
the names of child executables that Valgrind should not trace into. Patterns may
include the metacharacters ? and *, which have the usual meaning.
This can be useful for pruning uninteresting branches from a tree of processes being
run on Valgrind. But you should be careful when using it. When Valgrind skips tracing
into an executable, it doesn't just skip tracing that executable, it also skips
tracing any of that executable's child processes. In other words, the flag doesn't
merely cause tracing to stop at the specified executables -- it skips tracing of
entire process subtrees rooted at any of the specified executables.
--trace-children-skip-by-arg=patt1,patt2,...
This is the same as --trace-children-skip, with one difference: the decision as to
whether to trace into a child process is made by examining the arguments to the child
process, rather than the name of its executable.
--child-silent-after-fork=<yes|no> [default: no]
When enabled, Valgrind will not show any debugging or logging output for the child
process resulting from a fork call. This can make the output less confusing (although
more misleading) when dealing with processes that create children. It is particularly
useful in conjunction with --trace-children=. Use of this option is also strongly
recommended if you are requesting XML output (--xml=yes), since otherwise the XML from
child and parent may become mixed up, which usually makes it useless.
--vgdb=<no|yes|full> [default: yes]
Valgrind will provide "gdbserver" functionality when --vgdb=yes or --vgdb=full is
specified. This allows an external GNU GDB debugger to control and debug your program
when it runs on Valgrind. --vgdb=full incurs significant performance overheads, but
provides more precise breakpoints and watchpoints. See Debugging your program using
Valgrind's gdbserver and GDB for a detailed description.
If the embedded gdbserver is enabled but no gdb is currently being used, the vgdb
command line utility can send "monitor commands" to Valgrind from a shell. The
Valgrind core provides a set of Valgrind monitor commands. A tool can optionally
provide tool specific monitor commands, which are documented in the tool specific
chapter.
--vgdb-error=<number> [default: 999999999]
Use this option when the Valgrind gdbserver is enabled with --vgdb=yes or --vgdb=full.
Tools that report errors will wait for "number" errors to be reported before freezing
the program and waiting for you to connect with GDB. It follows that a value of zero
will cause the gdbserver to be started before your program is executed. This is
typically used to insert GDB breakpoints before execution, and also works with tools
that do not report errors, such as Massif.
--vgdb-stop-at=<set> [default: none]
Use this option when the Valgrind gdbserver is enabled with --vgdb=yes or --vgdb=full.
The Valgrind gdbserver will be invoked for each error after --vgdb-error have been
reported. You can additionally ask the Valgrind gdbserver to be invoked for other
events, specified in one of the following ways:
• a comma separated list of one or more of startup exit abexit valgrindabexit.
The values startup exit valgrindabexit respectively indicate to invoke gdbserver
before your program is executed, after the last instruction of your program, on
Valgrind abnormal exit (e.g. internal error, out of memory, ...).
The option abexit is similar to exit but tells to invoke gdbserver only when your
application exits abnormally (i.e. with an exit code different of 0).
Note: startup and --vgdb-error=0 will both cause Valgrind gdbserver to be invoked
before your program is executed. The --vgdb-error=0 will in addition cause your
program to stop on all subsequent errors.
• all to specify the complete set. It is equivalent to
--vgdb-stop-at=startup,exit,abexit,valgrindabexit.
• none for the empty set.
--track-fds=<yes|no|all> [default: no]
When enabled, Valgrind will print out a list of open file descriptors on exit or on
request, via the gdbserver monitor command v.info open_fds. Along with each file
descriptor is printed a stack backtrace of where the file was opened and any details
relating to the file descriptor such as the file name or socket details. Use all to
include reporting on stdin, stdout and stderr.
--time-stamp=<yes|no> [default: no]
When enabled, each message is preceded with an indication of the elapsed wallclock
time since startup, expressed as days, hours, minutes, seconds and milliseconds.
--log-fd=<number> [default: 2, stderr]
Specifies that Valgrind should send all of its messages to the specified file
descriptor. The default, 2, is the standard error channel (stderr). Note that this may
interfere with the client's own use of stderr, as Valgrind's output will be
interleaved with any output that the client sends to stderr.
--log-file=<filename>
Specifies that Valgrind should send all of its messages to the specified file. If the
file name is empty, it causes an abort. There are three special format specifiers that
can be used in the file name.
%p is replaced with the current process ID. This is very useful for program that
invoke multiple processes. WARNING: If you use --trace-children=yes and your program
invokes multiple processes OR your program forks without calling exec afterwards, and
you don't use this specifier (or the %q specifier below), the Valgrind output from all
those processes will go into one file, possibly jumbled up, and possibly incomplete.
Note: If the program forks and calls exec afterwards, Valgrind output of the child
from the period between fork and exec will be lost. Fortunately this gap is really
tiny for most programs; and modern programs use posix_spawn anyway.
%n is replaced with a file sequence number unique for this process. This is useful for
processes that produces several files from the same filename template.
%q{FOO} is replaced with the contents of the environment variable FOO. If the {FOO}
part is malformed, it causes an abort. This specifier is rarely needed, but very
useful in certain circumstances (eg. when running MPI programs). The idea is that you
specify a variable which will be set differently for each process in the job, for
example BPROC_RANK or whatever is applicable in your MPI setup. If the named
environment variable is not set, it causes an abort. Note that in some shells, the {
and } characters may need to be escaped with a backslash.
%% is replaced with %.
If an % is followed by any other character, it causes an abort.
If the file name specifies a relative file name, it is put in the program's initial
working directory: this is the current directory when the program started its
execution after the fork or after the exec. If it specifies an absolute file name (ie.
starts with '/') then it is put there.
--log-socket=<ip-address:port-number>
Specifies that Valgrind should send all of its messages to the specified port at the
specified IP address. The port may be omitted, in which case port 1500 is used. If a
connection cannot be made to the specified socket, Valgrind falls back to writing
output to the standard error (stderr). This option is intended to be used in
conjunction with the valgrind-listener program. For further details, see the
commentary in the manual.
--enable-debuginfod=<no|yes> [default: yes]
When enabled Valgrind will attempt to download missing debuginfo from debuginfod
servers if space-separated server URLs are present in the $DEBUGINFOD_URLS environment
variable. This option is supported on Linux only.
ERROR-RELATED OPTIONS
These options are used by all tools that can report errors, e.g. Memcheck, but not
Cachegrind.
--xml=<yes|no> [default: no]
When enabled, the important parts of the output (e.g. tool error messages) will be in
XML format rather than plain text. Furthermore, the XML output will be sent to a
different output channel than the plain text output. Therefore, you also must use one
of --xml-fd, --xml-file or --xml-socket to specify where the XML is to be sent.
Less important messages will still be printed in plain text, but because the XML
output and plain text output are sent to different output channels (the destination of
the plain text output is still controlled by --log-fd, --log-file and --log-socket)
this should not cause problems.
This option is aimed at making life easier for tools that consume Valgrind's output as
input, such as GUI front ends. Currently this option works with Memcheck, Helgrind and
DRD. The output format is specified in the file
docs/internals/xml-output-protocol4.txt in the source tree for Valgrind 3.5.0 or
later.
The recommended options for a GUI to pass, when requesting XML output, are: --xml=yes
to enable XML output, --xml-file to send the XML output to a (presumably GUI-selected)
file, --log-file to send the plain text output to a second GUI-selected file,
--child-silent-after-fork=yes, and -q to restrict the plain text output to critical
error messages created by Valgrind itself. For example, failure to read a specified
suppressions file counts as a critical error message. In this way, for a successful
run the text output file will be empty. But if it isn't empty, then it will contain
important information which the GUI user should be made aware of.
--xml-fd=<number> [default: -1, disabled]
Specifies that Valgrind should send its XML output to the specified file descriptor.
It must be used in conjunction with --xml=yes.
--xml-file=<filename>
Specifies that Valgrind should send its XML output to the specified file. It must be
used in conjunction with --xml=yes. Any %p or %q sequences appearing in the filename
are expanded in exactly the same way as they are for --log-file. See the description
of --log-file for details.
--xml-socket=<ip-address:port-number>
Specifies that Valgrind should send its XML output the specified port at the specified
IP address. It must be used in conjunction with --xml=yes. The form of the argument is
the same as that used by --log-socket. See the description of --log-socket for further
details.
--xml-user-comment=<string>
Embeds an extra user comment string at the start of the XML output. Only works when
--xml=yes is specified; ignored otherwise.
--demangle=<yes|no> [default: yes]
Enable/disable automatic demangling (decoding) of C++ names. Enabled by default. When
enabled, Valgrind will attempt to translate encoded C++ names back to something
approaching the original. The demangler handles symbols mangled by g++ versions 2.X,
3.X and 4.X.
An important fact about demangling is that function names mentioned in suppressions
files should be in their mangled form. Valgrind does not demangle function names when
searching for applicable suppressions, because to do otherwise would make suppression
file contents dependent on the state of Valgrind's demangling machinery, and also slow
down suppression matching.
--num-callers=<number> [default: 12]
Specifies the maximum number of entries shown in stack traces that identify program
locations. Note that errors are commoned up using only the top four function locations
(the place in the current function, and that of its three immediate callers). So this
doesn't affect the total number of errors reported.
The maximum value for this is 500. Note that higher settings will make Valgrind run a
bit more slowly and take a bit more memory, but can be useful when working with
programs with deeply-nested call chains.
--unw-stack-scan-thresh=<number> [default: 0] , --unw-stack-scan-frames=<number> [default:
5]
Stack-scanning support is available only on ARM targets.
These flags enable and control stack unwinding by stack scanning. When the normal
stack unwinding mechanisms -- usage of Dwarf CFI records, and frame-pointer following
-- fail, stack scanning may be able to recover a stack trace.
Note that stack scanning is an imprecise, heuristic mechanism that may give very
misleading results, or none at all. It should be used only in emergencies, when normal
unwinding fails, and it is important to nevertheless have stack traces.
Stack scanning is a simple technique: the unwinder reads words from the stack, and
tries to guess which of them might be return addresses, by checking to see if they
point just after ARM or Thumb call instructions. If so, the word is added to the
backtrace.
The main danger occurs when a function call returns, leaving its return address
exposed, and a new function is called, but the new function does not overwrite the old
address. The result of this is that the backtrace may contain entries for functions
which have already returned, and so be very confusing.
A second limitation of this implementation is that it will scan only the page (4KB,
normally) containing the starting stack pointer. If the stack frames are large, this
may result in only a few (or not even any) being present in the trace. Also, if you
are unlucky and have an initial stack pointer near the end of its containing page, the
scan may miss all interesting frames.
By default stack scanning is disabled. The normal use case is to ask for it when a
stack trace would otherwise be very short. So, to enable it, use
--unw-stack-scan-thresh=number. This requests Valgrind to try using stack scanning to
"extend" stack traces which contain fewer than number frames.
If stack scanning does take place, it will only generate at most the number of frames
specified by --unw-stack-scan-frames. Typically, stack scanning generates so many
garbage entries that this value is set to a low value (5) by default. In no case will
a stack trace larger than the value specified by --num-callers be created.
--error-limit=<yes|no> [default: yes]
When enabled, Valgrind stops reporting errors after 10,000,000 in total, or 1,000
different ones, have been seen. This is to stop the error tracking machinery from
becoming a huge performance overhead in programs with many errors.
--error-exitcode=<number> [default: 0]
Specifies an alternative exit code to return if Valgrind reported any errors in the
run. When set to the default value (zero), the return value from Valgrind will always
be the return value of the process being simulated. When set to a nonzero value, that
value is returned instead, if Valgrind detects any errors. This is useful for using
Valgrind as part of an automated test suite, since it makes it easy to detect test
cases for which Valgrind has reported errors, just by inspecting return codes. When
set to a nonzero value and Valgrind detects no error, the return value of Valgrind
will be the return value of the program being simulated.
--exit-on-first-error=<yes|no> [default: no]
If this option is enabled, Valgrind exits on the first error. A nonzero exit value
must be defined using --error-exitcode option. Useful if you are running regression
tests or have some other automated test machinery.
--error-markers=<begin>,<end> [default: none]
When errors are output as plain text (i.e. XML not used), --error-markers instructs to
output a line containing the begin (end) string before (after) each error.
Such marker lines facilitate searching for errors and/or extracting errors in an
output file that contain valgrind errors mixed with the program output.
Note that empty markers are accepted. So, only using a begin (or an end) marker is
possible.
--show-error-list=no|yes [default: no]
If this option is enabled, for tools that report errors, valgrind will show the list
of detected errors and the list of used suppressions at exit.
Note that at verbosity 2 and above, valgrind automatically shows the list of detected
errors and the list of used suppressions at exit, unless --show-error-list=no is
selected.
-s
Specifying -s is equivalent to --show-error-list=yes.
--sigill-diagnostics=<yes|no> [default: yes]
Enable/disable printing of illegal instruction diagnostics. Enabled by default, but
defaults to disabled when --quiet is given. The default can always be explicitly
overridden by giving this option.
When enabled, a warning message will be printed, along with some diagnostics, whenever
an instruction is encountered that Valgrind cannot decode or translate, before the
program is given a SIGILL signal. Often an illegal instruction indicates a bug in the
program or missing support for the particular instruction in Valgrind. But some
programs do deliberately try to execute an instruction that might be missing and trap
the SIGILL signal to detect processor features. Using this flag makes it possible to
avoid the diagnostic output that you would otherwise get in such cases.
--keep-debuginfo=<yes|no> [default: no]
When enabled, keep ("archive") symbols and all other debuginfo for unloaded code. This
allows saved stack traces to include file/line info for code that has been dlclose'd
(or similar). Be careful with this, since it can lead to unbounded memory use for
programs which repeatedly load and unload shared objects.
Some tools and some functionalities have only limited support for archived debug info.
Memcheck fully supports it. Generally, tools that report errors can use archived debug
info to show the error stack traces. The known limitations are: Helgrind's past access
stack trace of a race condition is does not use archived debug info. Massif (and more
generally the xtree Massif output format) does not make use of archived debug info.
Only Memcheck has been (somewhat) tested with --keep-debuginfo=yes, so other tools may
have unknown limitations.
--show-below-main=<yes|no> [default: no]
By default, stack traces for errors do not show any functions that appear beneath main
because most of the time it's uninteresting C library stuff and/or gobbledygook.
Alternatively, if main is not present in the stack trace, stack traces will not show
any functions below main-like functions such as glibc's __libc_start_main.
Furthermore, if main-like functions are present in the trace, they are normalised as
(below main), in order to make the output more deterministic.
If this option is enabled, all stack trace entries will be shown and main-like
functions will not be normalised.
--fullpath-after=<string> [default: don't show source paths]
By default Valgrind only shows the filenames in stack traces, but not full paths to
source files. When using Valgrind in large projects where the sources reside in
multiple different directories, this can be inconvenient. --fullpath-after provides a
flexible solution to this problem. When this option is present, the path to each
source file is shown, with the following all-important caveat: if string is found in
the path, then the path up to and including string is omitted, else the path is shown
unmodified. Note that string is not required to be a prefix of the path.
For example, consider a file named /home/janedoe/blah/src/foo/bar/xyzzy.c. Specifying
--fullpath-after=/home/janedoe/blah/src/ will cause Valgrind to show the name as
foo/bar/xyzzy.c.
Because the string is not required to be a prefix, --fullpath-after=src/ will produce
the same output. This is useful when the path contains arbitrary machine-generated
characters. For example, the path /my/build/dir/C32A1B47/blah/src/foo/xyzzy can be
pruned to foo/xyzzy using --fullpath-after=/blah/src/.
If you simply want to see the full path, just specify an empty string:
--fullpath-after=. This isn't a special case, merely a logical consequence of the
above rules.
Finally, you can use --fullpath-after multiple times. Any appearance of it causes
Valgrind to switch to producing full paths and applying the above filtering rule. Each
produced path is compared against all the --fullpath-after-specified strings, in the
order specified. The first string to match causes the path to be truncated as
described above. If none match, the full path is shown. This facilitates chopping off
prefixes when the sources are drawn from a number of unrelated directories.
--extra-debuginfo-path=<path> [default: undefined and unused]
By default Valgrind searches in several well-known paths for debug objects, such as
/usr/lib/debug/.
However, there may be scenarios where you may wish to put debug objects at an
arbitrary location, such as external storage when running Valgrind on a mobile device
with limited local storage. Another example might be a situation where you do not have
permission to install debug object packages on the system where you are running
Valgrind.
In these scenarios, you may provide an absolute path as an extra, final place for
Valgrind to search for debug objects by specifying
--extra-debuginfo-path=/path/to/debug/objects. The given path will be prepended to the
absolute path name of the searched-for object. For example, if Valgrind is looking for
the debuginfo for /w/x/y/zz.so and --extra-debuginfo-path=/a/b/c is specified, it will
look for a debug object at /a/b/c/w/x/y/zz.so.
This flag should only be specified once. If it is specified multiple times, only the
last instance is honoured.
--debuginfo-server=ipaddr:port [default: undefined and unused]
This is a new, experimental, feature introduced in version 3.9.0.
In some scenarios it may be convenient to read debuginfo from objects stored on a
different machine. With this flag, Valgrind will query a debuginfo server running on
ipaddr and listening on port port, if it cannot find the debuginfo object in the local
filesystem.
The debuginfo server must accept TCP connections on port port. The debuginfo server is
contained in the source file auxprogs/valgrind-di-server.c. It will only serve from
the directory it is started in. port defaults to 1500 in both client and server if
not specified.
If Valgrind looks for the debuginfo for /w/x/y/zz.so by using the debuginfo server, it
will strip the pathname components and merely request zz.so on the server. That in
turn will look only in its current working directory for a matching debuginfo object.
The debuginfo data is transmitted in small fragments (8 KB) as requested by Valgrind.
Each block is compressed using LZO to reduce transmission time. The implementation has
been tuned for best performance over a single-stage 802.11g (WiFi) network link.
Note that checks for matching primary vs debug objects, using GNU debuglink CRC
scheme, are performed even when using the debuginfo server. To disable such checking,
you need to also specify --allow-mismatched-debuginfo=yes.
By default the Valgrind build system will build valgrind-di-server for the target
platform, which is almost certainly not what you want. So far we have been unable to
find out how to get automake/autoconf to build it for the build platform. If you want
to use it, you will have to recompile it by hand using the command shown at the top of
auxprogs/valgrind-di-server.c.
Valgrind can also download debuginfo via debuginfod. See the DEBUGINFOD section for
more information.
--allow-mismatched-debuginfo=no|yes [no]
When reading debuginfo from separate debuginfo objects, Valgrind will by default check
that the main and debuginfo objects match, using the GNU debuglink mechanism. This
guarantees that it does not read debuginfo from out of date debuginfo objects, and
also ensures that Valgrind can't crash as a result of mismatches.
This check can be overridden using --allow-mismatched-debuginfo=yes. This may be
useful when the debuginfo and main objects have not been split in the proper way. Be
careful when using this, though: it disables all consistency checking, and Valgrind
has been observed to crash when the main and debuginfo objects don't match.
--suppressions=<filename> [default: $PREFIX/lib/valgrind/default.supp]
Specifies an extra file from which to read descriptions of errors to suppress. You may
use up to 100 extra suppression files.
--gen-suppressions=<yes|no|all> [default: no]
When set to yes, Valgrind will pause after every error shown and print the line:
---- Print suppression ? --- [Return/N/n/Y/y/C/c] ----
Pressing Ret, or N Ret or n Ret, causes Valgrind continue execution without printing a
suppression for this error.
Pressing Y Ret or y Ret causes Valgrind to write a suppression for this error. You can
then cut and paste it into a suppression file if you don't want to hear about the
error in the future.
When set to all, Valgrind will print a suppression for every reported error, without
querying the user.
This option is particularly useful with C++ programs, as it prints out the
suppressions with mangled names, as required.
Note that the suppressions printed are as specific as possible. You may want to common
up similar ones, by adding wildcards to function names, and by using frame-level
wildcards. The wildcarding facilities are powerful yet flexible, and with a bit of
careful editing, you may be able to suppress a whole family of related errors with
only a few suppressions.
Sometimes two different errors are suppressed by the same suppression, in which case
Valgrind will output the suppression more than once, but you only need to have one
copy in your suppression file (but having more than one won't cause problems). Also,
the suppression name is given as <insert a suppression name here>; the name doesn't
really matter, it's only used with the -v option which prints out all used suppression
records.
--input-fd=<number> [default: 0, stdin]
When using --gen-suppressions=yes, Valgrind will stop so as to read keyboard input
from you when each error occurs. By default it reads from the standard input (stdin),
which is problematic for programs which close stdin. This option allows you to specify
an alternative file descriptor from which to read input.
--dsymutil=no|yes [yes]
This option is only relevant when running Valgrind on macOS.
macOS uses a deferred debug information (debuginfo) linking scheme. When object files
containing debuginfo are linked into a .dylib or an executable, the debuginfo is not
copied into the final file. Instead, the debuginfo must be linked manually by running
dsymutil, a system-provided utility, on the executable or .dylib. The resulting
combined debuginfo is placed in a directory alongside the executable or .dylib, but
with the extension .dSYM.
With --dsymutil=no, Valgrind will detect cases where the .dSYM directory is either
missing, or is present but does not appear to match the associated executable or
.dylib, most likely because it is out of date. In these cases, Valgrind will print a
warning message but take no further action.
With --dsymutil=yes, Valgrind will, in such cases, automatically run dsymutil as
necessary to bring the debuginfo up to date. For all practical purposes, if you always
use --dsymutil=yes, then there is never any need to run dsymutil manually or as part
of your applications's build system, since Valgrind will run it as necessary.
Valgrind will not attempt to run dsymutil on any executable or library in /usr/,
/bin/, /sbin/, /opt/, /sw/, /System/, /Library/ or /Applications/ since dsymutil will
always fail in such situations. It fails both because the debuginfo for such
pre-installed system components is not available anywhere, and also because it would
require write privileges in those directories.
Be careful when using --dsymutil=yes, since it will cause pre-existing .dSYM
directories to be silently deleted and re-created. Also note that dsymutil is quite
slow, sometimes excessively so.
--max-stackframe=<number> [default: 2000000]
The maximum size of a stack frame. If the stack pointer moves by more than this amount
then Valgrind will assume that the program is switching to a different stack.
You may need to use this option if your program has large stack-allocated arrays.
Valgrind keeps track of your program's stack pointer. If it changes by more than the
threshold amount, Valgrind assumes your program is switching to a different stack, and
Memcheck behaves differently than it would for a stack pointer change smaller than the
threshold. Usually this heuristic works well. However, if your program allocates large
structures on the stack, this heuristic will be fooled, and Memcheck will subsequently
report large numbers of invalid stack accesses. This option allows you to change the
threshold to a different value.
You should only consider use of this option if Valgrind's debug output directs you to
do so. In that case it will tell you the new threshold you should specify.
In general, allocating large structures on the stack is a bad idea, because you can
easily run out of stack space, especially on systems with limited memory or which
expect to support large numbers of threads each with a small stack, and also because
the error checking performed by Memcheck is more effective for heap-allocated data
than for stack-allocated data. If you have to use this option, you may wish to
consider rewriting your code to allocate on the heap rather than on the stack.
--main-stacksize=<number> [default: use current 'ulimit' value]
Specifies the size of the main thread's stack.
To simplify its memory management, Valgrind reserves all required space for the main
thread's stack at startup. That means it needs to know the required stack size at
startup.
By default, Valgrind uses the current "ulimit" value for the stack size, or 16 MB,
whichever is lower. In many cases this gives a stack size in the range 8 to 16 MB,
which almost never overflows for most applications.
If you need a larger total stack size, use --main-stacksize to specify it. Only set it
as high as you need, since reserving far more space than you need (that is, hundreds
of megabytes more than you need) constrains Valgrind's memory allocators and may
reduce the total amount of memory that Valgrind can use. This is only really of
significance on 32-bit machines.
On Linux, you may request a stack of size up to 2GB. Valgrind will stop with a
diagnostic message if the stack cannot be allocated.
--main-stacksize only affects the stack size for the program's initial thread. It has
no bearing on the size of thread stacks, as Valgrind does not allocate those.
You may need to use both --main-stacksize and --max-stackframe together. It is
important to understand that --main-stacksize sets the maximum total stack size,
whilst --max-stackframe specifies the largest size of any one stack frame. You will
have to work out the --main-stacksize value for yourself (usually, if your
applications segfaults). But Valgrind will tell you the needed --max-stackframe size,
if necessary.
As discussed further in the description of --max-stackframe, a requirement for a large
stack is a sign of potential portability problems. You are best advised to place all
large data in heap-allocated memory.
--max-threads=<number> [default: 500]
By default, Valgrind can handle to up to 500 threads. Occasionally, that number is too
small. Use this option to provide a different limit. E.g. --max-threads=3000.
--realloc-zero-bytes-frees=yes|no [default: yes for glibc no otherwise]
The behaviour of realloc() is implementation defined (in C17, in C23 it is likely to
become undefined). Valgrind tries to work in the same way as the underlying OS and C
runtime library. However, if you use a different C runtime library then this default
may be wrong. For instance, if you use Valgrind on Linux installed via a package and
use the musl C runtime or the JEMalloc library then consider using
--realloc-zero-bytes-frees=no.
Address Sanitizer has a similar and even wordier option
allocator_frees_and_returns_null_on_realloc_zero.
MALLOC()-RELATED OPTIONS
For tools that use their own version of malloc (e.g. Memcheck, Massif, Helgrind, DRD), the
following options apply.
--alignment=<number> [default: 8 or 16, depending on the platform]
By default Valgrind's malloc, realloc, etc, return a block whose starting address is
8-byte aligned or 16-byte aligned (the value depends on the platform and matches the
platform default). This option allows you to specify a different alignment. The
supplied value must be greater than or equal to the default, less than or equal to
4096, and must be a power of two.
--redzone-size=<number> [default: depends on the tool]
Valgrind's malloc, realloc, etc, add padding blocks before and after each heap block
allocated by the program being run. Such padding blocks are called redzones. The
default value for the redzone size depends on the tool. For example, Memcheck adds and
protects a minimum of 16 bytes before and after each block allocated by the client.
This allows it to detect block underruns or overruns of up to 16 bytes.
Increasing the redzone size makes it possible to detect overruns of larger distances,
but increases the amount of memory used by Valgrind. Decreasing the redzone size will
reduce the memory needed by Valgrind but also reduces the chances of detecting
over/underruns, so is not recommended.
--xtree-memory=none|allocs|full [none]
Tools replacing Valgrind's malloc, realloc, etc, can optionally produce an execution
tree detailing which piece of code is responsible for heap memory usage. See Execution
Trees for a detailed explanation about execution trees.
When set to none, no memory execution tree is produced.
When set to allocs, the memory execution tree gives the current number of allocated
bytes and the current number of allocated blocks.
When set to full, the memory execution tree gives 6 different measurements : the
current number of allocated bytes and blocks (same values as for allocs), the total
number of allocated bytes and blocks, the total number of freed bytes and blocks.
Note that the overhead in cpu and memory to produce an xtree depends on the tool. The
overhead in cpu is small for the value allocs, as the information needed to produce
this report is maintained in any case by the tool. For massif and helgrind, specifying
full implies to capture a stack trace for each free operation, while normally these
tools only capture an allocation stack trace. For Memcheck, the cpu overhead for the
value full is small, as this can only be used in combination with
--keep-stacktraces=alloc-and-free or --keep-stacktraces=alloc-then-free, which already
records a stack trace for each free operation. The memory overhead varies between 5
and 10 words per unique stacktrace in the xtree, plus the memory needed to record the
stack trace for the free operations, if needed specifically for the xtree.
--xtree-memory-file=<filename> [default: xtmemory.kcg.%p]
Specifies that Valgrind should produce the xtree memory report in the specified file.
Any %p or %q sequences appearing in the filename are expanded in exactly the same way
as they are for --log-file. See the description of --log-file for details.
If the filename contains the extension .ms, then the produced file format will be a
massif output file format. If the filename contains the extension .kcg or no extension
is provided or recognised, then the produced file format will be a callgrind output
format.
See Execution Trees for a detailed explanation about execution trees formats.
UNCOMMON OPTIONS
These options apply to all tools, as they affect certain obscure workings of the Valgrind
core. Most people won't need to use them.
--smc-check=<none|stack|all|all-non-file> [default: all-non-file for x86/amd64/s390x,
stack for other archs]
This option controls Valgrind's detection of self-modifying code. If no checking is
done, when a program executes some code, then overwrites it with new code, and
executes the new code, Valgrind will continue to execute the translations it made for
the old code. This will likely lead to incorrect behaviour and/or crashes.
For "modern" architectures -- anything that's not x86, amd64 or s390x -- the default
is stack. This is because a correct program must take explicit action to reestablish
D-I cache coherence following code modification. Valgrind observes and honours such
actions, with the result that self-modifying code is transparently handled with zero
extra cost.
For x86, amd64 and s390x, the program is not required to notify the hardware of
required D-I coherence syncing. Hence the default is all-non-file, which covers the
normal case of generating code into an anonymous (non-file-backed) mmap'd area.
The meanings of the four available settings are as follows. No detection (none),
detect self-modifying code on the stack (which is used by GCC to implement nested
functions) (stack), detect self-modifying code everywhere (all), and detect
self-modifying code everywhere except in file-backed mappings (all-non-file).
Running with all will slow Valgrind down noticeably. Running with none will rarely
speed things up, since very little code gets dynamically generated in most programs.
The VALGRIND_DISCARD_TRANSLATIONS client request is an alternative to --smc-check=all
and --smc-check=all-non-file that requires more programmer effort but allows Valgrind
to run your program faster, by telling it precisely when translations need to be
re-made.
--smc-check=all-non-file provides a cheaper but more limited version of
--smc-check=all. It adds checks to any translations that do not originate from
file-backed memory mappings. Typical applications that generate code, for example JITs
in web browsers, generate code into anonymous mmaped areas, whereas the "fixed" code
of the browser always lives in file-backed mappings. --smc-check=all-non-file takes
advantage of this observation, limiting the overhead of checking to code which is
likely to be JIT generated.
--read-inline-info=<yes|no> [default: see below]
When enabled, Valgrind will read information about inlined function calls from DWARF3
debug info. This slows Valgrind startup and makes it use more memory (typically for
each inlined piece of code, 6 words and space for the function name), but it results
in more descriptive stacktraces. Currently, this functionality is enabled by default
only for Linux, Android and Solaris targets and only for the tools Memcheck, Massif,
Helgrind and DRD. Here is an example of some stacktraces with --read-inline-info=no:
==15380== Conditional jump or move depends on uninitialised value(s)
==15380== at 0x80484EA: main (inlinfo.c:6)
==15380==
==15380== Conditional jump or move depends on uninitialised value(s)
==15380== at 0x8048550: fun_noninline (inlinfo.c:6)
==15380== by 0x804850E: main (inlinfo.c:34)
==15380==
==15380== Conditional jump or move depends on uninitialised value(s)
==15380== at 0x8048520: main (inlinfo.c:6)
And here are the same errors with --read-inline-info=yes:
==15377== Conditional jump or move depends on uninitialised value(s)
==15377== at 0x80484EA: fun_d (inlinfo.c:6)
==15377== by 0x80484EA: fun_c (inlinfo.c:14)
==15377== by 0x80484EA: fun_b (inlinfo.c:20)
==15377== by 0x80484EA: fun_a (inlinfo.c:26)
==15377== by 0x80484EA: main (inlinfo.c:33)
==15377==
==15377== Conditional jump or move depends on uninitialised value(s)
==15377== at 0x8048550: fun_d (inlinfo.c:6)
==15377== by 0x8048550: fun_noninline (inlinfo.c:41)
==15377== by 0x804850E: main (inlinfo.c:34)
==15377==
==15377== Conditional jump or move depends on uninitialised value(s)
==15377== at 0x8048520: fun_d (inlinfo.c:6)
==15377== by 0x8048520: main (inlinfo.c:35)
--read-var-info=<yes|no> [default: no]
When enabled, Valgrind will read information about variable types and locations from
DWARF3 debug info. This slows Valgrind startup significantly and makes it use
significantly more memory, but for the tools that can take advantage of it (Memcheck,
Helgrind, DRD) it can result in more precise error messages. For example, here are
some standard errors issued by Memcheck:
==15363== Uninitialised byte(s) found during client check request
==15363== at 0x80484A9: croak (varinfo1.c:28)
==15363== by 0x8048544: main (varinfo1.c:55)
==15363== Address 0x80497f7 is 7 bytes inside data symbol "global_i2"
==15363==
==15363== Uninitialised byte(s) found during client check request
==15363== at 0x80484A9: croak (varinfo1.c:28)
==15363== by 0x8048550: main (varinfo1.c:56)
==15363== Address 0xbea0d0cc is on thread 1's stack
==15363== in frame #1, created by main (varinfo1.c:45)
And here are the same errors with --read-var-info=yes:
==15370== Uninitialised byte(s) found during client check request
==15370== at 0x80484A9: croak (varinfo1.c:28)
==15370== by 0x8048544: main (varinfo1.c:55)
==15370== Location 0x80497f7 is 0 bytes inside global_i2[7],
==15370== a global variable declared at varinfo1.c:41
==15370==
==15370== Uninitialised byte(s) found during client check request
==15370== at 0x80484A9: croak (varinfo1.c:28)
==15370== by 0x8048550: main (varinfo1.c:56)
==15370== Location 0xbeb4a0cc is 0 bytes inside local var "local"
==15370== declared at varinfo1.c:46, in frame #1 of thread 1
--vgdb-poll=<number> [default: 5000]
As part of its main loop, the Valgrind scheduler will poll to check if some activity
(such as an external command or some input from a gdb) has to be handled by gdbserver.
This activity poll will be done after having run the given number of basic blocks (or
slightly more than the given number of basic blocks). This poll is quite cheap so the
default value is set relatively low. You might further decrease this value if vgdb
cannot use ptrace system call to interrupt Valgrind if all threads are (most of the
time) blocked in a system call.
--vgdb-shadow-registers=no|yes [default: no]
When activated, gdbserver will expose the Valgrind shadow registers to GDB. With this,
the value of the Valgrind shadow registers can be examined or changed using GDB.
Exposing shadow registers only works with GDB version 7.1 or later.
--vgdb-prefix=<prefix> [default: /tmp/vgdb-pipe]
To communicate with gdb/vgdb, the Valgrind gdbserver creates 3 files (2 named FIFOs
and a mmap shared memory file). The prefix option controls the directory and prefix
for the creation of these files.
--run-libc-freeres=<yes|no> [default: yes]
This option is only relevant when running Valgrind on Linux.
The GNU C library (libc.so), which is used by all programs, may allocate memory for
its own uses. Usually it doesn't bother to free that memory when the program ends—
there would be no point, since the Linux kernel reclaims all process resources when a
process exits anyway, so it would just slow things down.
The glibc authors realised that this behaviour causes leak checkers, such as Valgrind,
to falsely report leaks in glibc, when a leak check is done at exit. In order to avoid
this, they provided a routine called __libc_freeres specifically to make glibc release
all memory it has allocated. Memcheck therefore tries to run __libc_freeres at exit.
Unfortunately, in some very old versions of glibc, __libc_freeres is sufficiently
buggy to cause segmentation faults. This was particularly noticeable on Red Hat 7.1.
So this option is provided in order to inhibit the run of __libc_freeres. If your
program seems to run fine on Valgrind, but segfaults at exit, you may find that
--run-libc-freeres=no fixes that, although at the cost of possibly falsely reporting
space leaks in libc.so.
--run-cxx-freeres=<yes|no> [default: yes]
This option is only relevant when running Valgrind on Linux or Solaris C++ programs.
The GNU Standard C++ library (libstdc++.so), which is used by all C++ programs
compiled with g++, may allocate memory for its own uses. Usually it doesn't bother to
free that memory when the program ends—there would be no point, since the kernel
reclaims all process resources when a process exits anyway, so it would just slow
things down.
The gcc authors realised that this behaviour causes leak checkers, such as Valgrind,
to falsely report leaks in libstdc++, when a leak check is done at exit. In order to
avoid this, they provided a routine called __gnu_cxx::__freeres specifically to make
libstdc++ release all memory it has allocated. Memcheck therefore tries to run
__gnu_cxx::__freeres at exit.
For the sake of flexibility and unforeseen problems with __gnu_cxx::__freeres, option
--run-cxx-freeres=no exists, although at the cost of possibly falsely reporting space
leaks in libstdc++.so.
--sim-hints=hint1,hint2,...
Pass miscellaneous hints to Valgrind which slightly modify the simulated behaviour in
nonstandard or dangerous ways, possibly to help the simulation of strange features. By
default no hints are enabled. Use with caution! Currently known hints are:
• lax-ioctls: Be very lax about ioctl handling; the only assumption is that the size
is correct. Doesn't require the full buffer to be initialised when writing.
Without this, using some device drivers with a large number of strange ioctl
commands becomes very tiresome.
• fuse-compatible: Enable special handling for certain system calls that may block
in a FUSE file-system. This may be necessary when running Valgrind on a
multi-threaded program that uses one thread to manage a FUSE file-system and
another thread to access that file-system.
• enable-outer: Enable some special magic needed when the program being run is
itself Valgrind.
• no-inner-prefix: Disable printing a prefix > in front of each stdout or stderr
output line in an inner Valgrind being run by an outer Valgrind. This is useful
when running Valgrind regression tests in an outer/inner setup. Note that the
prefix > will always be printed in front of the inner debug logging lines.
• no-nptl-pthread-stackcache: This hint is only relevant when running Valgrind on
Linux; it is ignored on FreeBSD, Solaris and macOS.
The GNU glibc pthread library (libpthread.so), which is used by pthread programs,
maintains a cache of pthread stacks. When a pthread terminates, the memory used
for the pthread stack and some thread local storage related data structure are not
always directly released. This memory is kept in a cache (up to a certain size),
and is re-used if a new thread is started.
This cache causes the helgrind tool to report some false positive race condition
errors on this cached memory, as helgrind does not understand the internal glibc
cache synchronisation primitives. So, when using helgrind, disabling the cache
helps to avoid false positive race conditions, in particular when using thread
local storage variables (e.g. variables using the __thread qualifier).
When using the memcheck tool, disabling the cache ensures the memory used by glibc
to handle __thread variables is directly released when a thread terminates.
Note: Valgrind disables the cache using some internal knowledge of the glibc stack
cache implementation and by examining the debug information of the pthread
library. This technique is thus somewhat fragile and might not work for all glibc
versions. This has been successfully tested with various glibc versions (e.g.
2.11, 2.16, 2.18) on various platforms.
• lax-doors: (Solaris only) Be very lax about door syscall handling over
unrecognised door file descriptors. Does not require that full buffer is
initialised when writing. Without this, programs using libdoor(3LIB) functionality
with completely proprietary semantics may report large number of false positives.
• fallback-llsc: (MIPS and ARM64 only): Enables an alternative implementation of
Load-Linked (LL) and Store-Conditional (SC) instructions. The standard
implementation gives more correct behaviour, but can cause indefinite looping on
certain processor implementations that are intolerant of extra memory references
between LL and SC. So far this is known only to happen on Cavium 3 cores. You
should not need to use this flag, since the relevant cores are detected at startup
and the alternative implementation is automatically enabled if necessary. There is
no equivalent anti-flag: you cannot force-disable the alternative implementation,
if it is automatically enabled. The underlying problem exists because the
"standard" implementation of LL and SC is done by copying through LL and SC
instructions into the instrumented code. However, tools may insert extra
instrumentation memory references in between the LL and SC instructions. These
memory references are not present in the original uninstrumented code, and their
presence in the instrumented code can cause the SC instructions to persistently
fail, leading to indefinite looping in LL-SC blocks. The alternative
implementation gives correct behaviour of LL and SC instructions between threads
in a process, up to and including the ABA scenario. It also gives correct
behaviour between a Valgrinded thread and a non-Valgrinded thread running in a
different process, that communicate via shared memory, but only up to and
including correct CAS behaviour -- in this case the ABA scenario may not be
correctly handled.
--scheduling-quantum=<number> [default: 100000]
The --scheduling-quantum option controls the maximum number of basic blocks executed
by a thread before releasing the lock used by Valgrind to serialise thread execution.
Smaller values give finer interleaving but increases the scheduling overhead. Finer
interleaving can be useful to reproduce race conditions with helgrind or DRD. For more
details about the Valgrind thread serialisation scheme and its impact on performance
and thread scheduling, see Scheduling and Multi-Thread Performance.
--fair-sched=<no|yes|try> [default: no]
The --fair-sched option controls the locking mechanism used by Valgrind to serialise
thread execution. The locking mechanism controls the way the threads are scheduled,
and different settings give different trade-offs between fairness and performance. For
more details about the Valgrind thread serialisation scheme and its impact on
performance and thread scheduling, see Scheduling and Multi-Thread Performance.
• The value --fair-sched=yes activates a fair scheduler. In short, if multiple
threads are ready to run, the threads will be scheduled in a round robin fashion.
This mechanism is not available on all platforms or Linux versions. If not
available, using --fair-sched=yes will cause Valgrind to terminate with an error.
You may find this setting improves overall responsiveness if you are running an
interactive multithreaded program, for example a web browser, on Valgrind.
• The value --fair-sched=try activates fair scheduling if available on the platform.
Otherwise, it will automatically fall back to --fair-sched=no.
• The value --fair-sched=no activates a scheduler which does not guarantee fairness
between threads ready to run, but which in general gives the highest performance.
--kernel-variant=variant1,variant2,...
Handle system calls and ioctls arising from minor variants of the default kernel for
this platform. This is useful for running on hacked kernels or with kernel modules
which support nonstandard ioctls, for example. Use with caution. If you don't
understand what this option does then you almost certainly don't need it. Currently
known variants are:
• bproc: support the sys_broc system call on x86. This is for running on BProc,
which is a minor variant of standard Linux which is sometimes used for building
clusters.
• android-no-hw-tls: some versions of the Android emulator for ARM do not provide a
hardware TLS (thread-local state) register, and Valgrind crashes at startup. Use
this variant to select software support for TLS.
• android-gpu-sgx5xx: use this to support handling of proprietary ioctls for the
PowerVR SGX 5XX series of GPUs on Android devices. Failure to select this does not
cause stability problems, but may cause Memcheck to report false errors after the
program performs GPU-specific ioctls.
• android-gpu-adreno3xx: similarly, use this to support handling of proprietary
ioctls for the Qualcomm Adreno 3XX series of GPUs on Android devices.
--merge-recursive-frames=<number> [default: 0]
Some recursive algorithms, for example balanced binary tree implementations, create
many different stack traces, each containing cycles of calls. A cycle is defined as
two identical program counter values separated by zero or more other program counter
values. Valgrind may then use a lot of memory to store all these stack traces. This is
a poor use of memory considering that such stack traces contain repeated uninteresting
recursive calls instead of more interesting information such as the function that has
initiated the recursive call.
The option --merge-recursive-frames=<number> instructs Valgrind to detect and merge
recursive call cycles having a size of up to <number> frames. When such a cycle is
detected, Valgrind records the cycle in the stack trace as a unique program counter.
The value 0 (the default) causes no recursive call merging. A value of 1 will cause
stack traces of simple recursive algorithms (for example, a factorial implementation)
to be collapsed. A value of 2 will usually be needed to collapse stack traces produced
by recursive algorithms such as binary trees, quick sort, etc. Higher values might be
needed for more complex recursive algorithms.
Note: recursive calls are detected by analysis of program counter values. They are not
detected by looking at function names.
--num-transtab-sectors=<number> [default: 6 for Android platforms, 16 for all others]
Valgrind translates and instruments your program's machine code in small fragments
(basic blocks). The translations are stored in a translation cache that is divided
into a number of sections (sectors). If the cache is full, the sector containing the
oldest translations is emptied and reused. If these old translations are needed again,
Valgrind must re-translate and re-instrument the corresponding machine code, which is
expensive. If the "executed instructions" working set of a program is big, increasing
the number of sectors may improve performance by reducing the number of
re-translations needed. Sectors are allocated on demand. Once allocated, a sector can
never be freed, and occupies considerable space, depending on the tool and the value
of --avg-transtab-entry-size (about 40 MB per sector for Memcheck). Use the option
--stats=yes to obtain precise information about the memory used by a sector and the
allocation and recycling of sectors.
--avg-transtab-entry-size=<number> [default: 0, meaning use tool provided default]
Average size of translated basic block. This average size is used to dimension the
size of a sector. Each tool provides a default value to be used. If this default value
is too small, the translation sectors will become full too quickly. If this default
value is too big, a significant part of the translation sector memory will be unused.
Note that the average size of a basic block translation depends on the tool, and might
depend on tool options. For example, the memcheck option --track-origins=yes increases
the size of the basic block translations. Use --avg-transtab-entry-size to tune the
size of the sectors, either to gain memory or to avoid too many retranslations.
--aspace-minaddr=<address> [default: depends on the platform]
To avoid potential conflicts with some system libraries, Valgrind does not use the
address space below --aspace-minaddr value, keeping it reserved in case a library
specifically requests memory in this region. So, some "pessimistic" value is guessed
by Valgrind depending on the platform. On linux, by default, Valgrind avoids using the
first 64MB even if typically there is no conflict in this complete zone. You can use
the option --aspace-minaddr to have your memory hungry application benefitting from
more of this lower memory. On the other hand, if you encounter a conflict, increasing
aspace-minaddr value might solve it. Conflicts will typically manifest themselves with
mmap failures in the low range of the address space. The provided address must be page
aligned and must be equal or bigger to 0x1000 (4KB). To find the default value on your
platform, do something such as valgrind -d -d date 2>&1 | grep -i minaddr. Values
lower than 0x10000 (64KB) are known to create problems on some distributions.
--valgrind-stacksize=<number> [default: 1MB]
For each thread, Valgrind needs its own 'private' stack. The default size for these
stacks is largely dimensioned, and so should be sufficient in most cases. In case the
size is too small, Valgrind will segfault. Before segfaulting, a warning might be
produced by Valgrind when approaching the limit.
Use the option --valgrind-stacksize if such an (unlikely) warning is produced, or
Valgrind dies due to a segmentation violation. Such segmentation violations have been
seen when demangling huge C++ symbols.
If your application uses many threads and needs a lot of memory, you can gain some
memory by reducing the size of these Valgrind stacks using the option
--valgrind-stacksize.
--show-emwarns=<yes|no> [default: no]
When enabled, Valgrind will emit warnings about its CPU emulation in certain cases.
These are usually not interesting.
--require-text-symbol=:sonamepatt:fnnamepatt
When a shared object whose soname matches sonamepatt is loaded into the process,
examine all the text symbols it exports. If none of those match fnnamepatt, print an
error message and abandon the run. This makes it possible to ensure that the run does
not continue unless a given shared object contains a particular function name.
Both sonamepatt and fnnamepatt can be written using the usual ? and * wildcards. For
example: ":*libc.so*:foo?bar". You may use characters other than a colon to separate
the two patterns. It is only important that the first character and the separator
character are the same. For example, the above example could also be written
"Q*libc.so*Qfoo?bar". Multiple
--require-text-symbol flags are allowed, in which case shared objects that are loaded
into the process will be checked against all of them.
The purpose of this is to support reliable usage of marked-up libraries. For example,
suppose we have a version of GCC's libgomp.so which has been marked up with
annotations to support Helgrind. It is only too easy and confusing to load the wrong,
un-annotated libgomp.so into the application. So the idea is: add a text symbol in the
marked-up library, for example annotated_for_helgrind_3_6, and then give the flag
--require-text-symbol=:*libgomp*so*:annotated_for_helgrind_3_6 so that when libgomp.so
is loaded, Valgrind scans its symbol table, and if the symbol isn't present the run is
aborted, rather than continuing silently with the un-marked-up library. Note that you
should put the entire flag in quotes to stop shells expanding up the * and ?
wildcards.
--soname-synonyms=syn1=pattern1,syn2=pattern2,...
When a shared library is loaded, Valgrind checks for functions in the library that
must be replaced or wrapped. For example, Memcheck replaces some string and memory
functions (strchr, strlen, strcpy, memchr, memcpy, memmove, etc.) with its own
versions. Such replacements are normally done only in shared libraries whose soname
matches a predefined soname pattern (e.g. libc.so* on linux). By default, no
replacement is done for a statically linked binary or for alternative libraries,
except for the allocation functions (malloc, free, calloc, memalign, realloc, operator
new, operator delete, etc.) Such allocation functions are intercepted by default in
any shared library or in the executable if they are exported as global symbols. This
means that if a replacement allocation library such as tcmalloc is found, its
functions are also intercepted by default. In some cases, the replacements allow
--soname-synonyms to specify one additional synonym pattern, giving flexibility in the
replacement. Or to prevent interception of all public allocation symbols.
Currently, this flexibility is only allowed for the malloc related functions, using
the synonym somalloc. This synonym is usable for all tools doing standard replacement
of malloc related functions (e.g. memcheck, helgrind, drd, massif, dhat).
• Alternate malloc library: to replace the malloc related functions in a specific
alternate library with soname mymalloclib.so (and not in any others), give the
option --soname-synonyms=somalloc=mymalloclib.so. A pattern can be used to match
multiple libraries sonames. For example, --soname-synonyms=somalloc=*tcmalloc*
will match the soname of all variants of the tcmalloc library (native, debug,
profiled, ... tcmalloc variants).
Note: the soname of a elf shared library can be retrieved using the readelf
utility.
• Replacements in a statically linked library are done by using the NONE pattern.
For example, if you link with libtcmalloc.a, and only want to intercept the malloc
related functions in the executable (and standard libraries) themselves, but not
any other shared libraries, you can give the option
--soname-synonyms=somalloc=NONE. Note that a NONE pattern will match the main
executable and any shared library having no soname.
• To run a "default" Firefox build for Linux, in which JEMalloc is linked in to the
main executable, use --soname-synonyms=somalloc=NONE.
• To only intercept allocation symbols in the default system libraries, but not in
any other shared library or the executable defining public malloc or operator new
related functions use a non-existing library name like
--soname-synonyms=somalloc=nouserintercepts (where nouserintercepts can be any
non-existing library name).
• Shared library of the dynamic (runtime) linker is excluded from searching for
global public symbols, such as those for the malloc related functions (identified
by somalloc synonym).
--progress-interval=<number> [default: 0, meaning 'disabled']
This is an enhancement to Valgrind's debugging output. It is unlikely to be of
interest to end users.
When number is set to a non-zero value, Valgrind will print a one-line progress
summary every number seconds. Valid settings for number are between 0 and 3600
inclusive. Here's some example output with number set to 10:
PROGRESS: U 110s, W 113s, 97.3% CPU, EvC 414.79M, TIn 616.7k, TOut 0.5k, #thr 67
PROGRESS: U 120s, W 124s, 96.8% CPU, EvC 505.27M, TIn 636.6k, TOut 3.0k, #thr 64
PROGRESS: U 130s, W 134s, 97.0% CPU, EvC 574.90M, TIn 657.5k, TOut 3.0k, #thr 63
Each line shows:
• U: total user time
• W: total wallclock time
• CPU: overall average cpu use
• EvC: number of event checks. An event check is a backwards branch in the simulated
program, so this is a measure of forward progress of the program
• TIn: number of code blocks instrumented by the JIT
• TOut: number of instrumented code blocks that have been thrown away
• #thr: number of threads in the program
From the progress of these, it is possible to observe:
• when the program is compute bound (TIn rises slowly, EvC rises rapidly)
• when the program is in a spinloop (TIn/TOut fixed, EvC rises rapidly)
• when the program is JIT-bound (TIn rises rapidly)
• when the program is rapidly discarding code (TOut rises rapidly)
• when the program is about to achieve some expected state (EvC arrives at some
value you expect)
• when the program is idling (U rises more slowly than W)
DEBUGGING VALGRIND OPTIONS
There are also some options for debugging Valgrind itself. You shouldn't need to use them
in the normal run of things. If you wish to see the list, use the --help-debug option.
MEMCHECK OPTIONS
--leak-check=<no|summary|yes|full> [default: summary]
When enabled, search for memory leaks when the client program finishes. If set to
summary, it says how many leaks occurred. If set to full or yes, each individual leak
will be shown in detail and/or counted as an error, as specified by the options
--show-leak-kinds and --errors-for-leak-kinds.
If --xml=yes is given, memcheck will automatically use the value --leak-check=full.
You can use --show-leak-kinds=none to reduce the size of the xml output if you are not
interested in the leak results.
--leak-resolution=<low|med|high> [default: high]
When doing leak checking, determines how willing Memcheck is to consider different
backtraces to be the same for the purposes of merging multiple leaks into a single
leak report. When set to low, only the first two entries need match. When med, four
entries have to match. When high, all entries need to match.
For hardcore leak debugging, you probably want to use --leak-resolution=high together
with --num-callers=40 or some such large number.
Note that the --leak-resolution setting does not affect Memcheck's ability to find
leaks. It only changes how the results are presented.
--show-leak-kinds=<set> [default: definite,possible]
Specifies the leak kinds to show in a full leak search, in one of the following ways:
• a comma separated list of one or more of definite indirect possible reachable.
• all to specify the complete set (all leak kinds). It is equivalent to
--show-leak-kinds=definite,indirect,possible,reachable.
• none for the empty set.
--errors-for-leak-kinds=<set> [default: definite,possible]
Specifies the leak kinds to count as errors in a full leak search. The <set> is
specified similarly to --show-leak-kinds
--leak-check-heuristics=<set> [default: all]
Specifies the set of leak check heuristics to be used during leak searches. The
heuristics control which interior pointers to a block cause it to be considered as
reachable. The heuristic set is specified in one of the following ways:
• a comma separated list of one or more of stdstring length64 newarray
multipleinheritance.
• all to activate the complete set of heuristics. It is equivalent to
--leak-check-heuristics=stdstring,length64,newarray,multipleinheritance.
• none for the empty set.
Note that these heuristics are dependent on the layout of the objects produced by the
C++ compiler. They have been tested with some gcc versions (e.g. 4.4 and 4.7). They
might not work properly with other C++ compilers.
--show-reachable=<yes|no> , --show-possibly-lost=<yes|no>
These options provide an alternative way to specify the leak kinds to show:
• --show-reachable=no --show-possibly-lost=yes is equivalent to
--show-leak-kinds=definite,possible.
• --show-reachable=no --show-possibly-lost=no is equivalent to
--show-leak-kinds=definite.
• --show-reachable=yes is equivalent to --show-leak-kinds=all.
Note that --show-possibly-lost=no has no effect if --show-reachable=yes is specified.
--xtree-leak=<no|yes> [no]
If set to yes, the results for the leak search done at exit will be output in a
'Callgrind Format' execution tree file. Note that this automatically sets the options
--leak-check=full and --show-leak-kinds=all, to allow xtree visualisation tools such
as kcachegrind to select what kind to leak to visualise. The produced file will
contain the following events:
• RB : Reachable Bytes
• PB : Possibly lost Bytes
• IB : Indirectly lost Bytes
• DB : Definitely lost Bytes (direct plus indirect)
• DIB : Definitely Indirectly lost Bytes (subset of DB)
• RBk : reachable Blocks
• PBk : Possibly lost Blocks
• IBk : Indirectly lost Blocks
• DBk : Definitely lost Blocks
The increase or decrease for all events above will also be output in the file to
provide the delta (increase or decrease) between 2 successive leak searches. For
example, iRB is the increase of the RB event, dPBk is the decrease of PBk event. The
values for the increase and decrease events will be zero for the first leak search
done.
See Execution Trees for a detailed explanation about execution trees.
--xtree-leak-file=<filename> [default: xtleak.kcg.%p]
Specifies that Valgrind should produce the xtree leak report in the specified file.
Any %p, %q or %n sequences appearing in the filename are expanded in exactly the same
way as they are for --log-file. See the description of --log-file for details.
See Execution Trees for a detailed explanation about execution trees formats.
--undef-value-errors=<yes|no> [default: yes]
Controls whether Memcheck reports uses of undefined value errors. Set this to no if
you don't want to see undefined value errors. It also has the side effect of speeding
up Memcheck somewhat. AddrCheck (removed in Valgrind 3.1.0) functioned like Memcheck
with --undef-value-errors=no.
--track-origins=<yes|no> [default: no]
Controls whether Memcheck tracks the origin of uninitialised values. By default, it
does not, which means that although it can tell you that an uninitialised value is
being used in a dangerous way, it cannot tell you where the uninitialised value came
from. This often makes it difficult to track down the root problem.
When set to yes, Memcheck keeps track of the origins of all uninitialised values.
Then, when an uninitialised value error is reported, Memcheck will try to show the
origin of the value. An origin can be one of the following four places: a heap block,
a stack allocation, a client request, or miscellaneous other sources (eg, a call to
brk).
For uninitialised values originating from a heap block, Memcheck shows where the block
was allocated. For uninitialised values originating from a stack allocation, Memcheck
can tell you which function allocated the value, but no more than that -- typically it
shows you the source location of the opening brace of the function. So you should
carefully check that all of the function's local variables are initialised properly.
Performance overhead: origin tracking is expensive. It halves Memcheck's speed and
increases memory use by a minimum of 100MB, and possibly more. Nevertheless it can
drastically reduce the effort required to identify the root cause of uninitialised
value errors, and so is often a programmer productivity win, despite running more
slowly.
Accuracy: Memcheck tracks origins quite accurately. To avoid very large space and time
overheads, some approximations are made. It is possible, although unlikely, that
Memcheck will report an incorrect origin, or not be able to identify any origin.
Note that the combination --track-origins=yes and --undef-value-errors=no is
nonsensical. Memcheck checks for and rejects this combination at startup.
--partial-loads-ok=<yes|no> [default: yes]
Controls how Memcheck handles 32-, 64-, 128- and 256-bit naturally aligned loads from
addresses for which some bytes are addressable and others are not. When yes, such
loads do not produce an address error. Instead, loaded bytes originating from illegal
addresses are marked as uninitialised, and those corresponding to legal addresses are
handled in the normal way.
When no, loads from partially invalid addresses are treated the same as loads from
completely invalid addresses: an illegal-address error is issued, and the resulting
bytes are marked as initialised.
Note that code that behaves in this way is in violation of the ISO C/C++ standards,
and should be considered broken. If at all possible, such code should be fixed.
--expensive-definedness-checks=<no|auto|yes> [default: auto]
Controls whether Memcheck should employ more precise but also more expensive (time
consuming) instrumentation when checking the definedness of certain values. In
particular, this affects the instrumentation of integer adds, subtracts and equality
comparisons.
Selecting --expensive-definedness-checks=yes causes Memcheck to use the most accurate
analysis possible. This minimises false error rates but can cause up to 30%
performance degradation.
Selecting --expensive-definedness-checks=no causes Memcheck to use the cheapest
instrumentation possible. This maximises performance but will normally give an
unusably high false error rate.
The default setting, --expensive-definedness-checks=auto, is strongly recommended.
This causes Memcheck to use the minimum of expensive instrumentation needed to achieve
the same false error rate as --expensive-definedness-checks=yes. It also enables an
instrumentation-time analysis pass which aims to further reduce the costs of accurate
instrumentation. Overall, the performance loss is generally around 5% relative to
--expensive-definedness-checks=no, although this is strongly workload dependent. Note
that the exact instrumentation settings in this mode are architecture dependent.
--keep-stacktraces=alloc|free|alloc-and-free|alloc-then-free|none [default:
alloc-and-free]
Controls which stack trace(s) to keep for malloc'd and/or free'd blocks.
With alloc-then-free, a stack trace is recorded at allocation time, and is associated
with the block. When the block is freed, a second stack trace is recorded, and this
replaces the allocation stack trace. As a result, any "use after free" errors relating
to this block can only show a stack trace for where the block was freed.
With alloc-and-free, both allocation and the deallocation stack traces for the block
are stored. Hence a "use after free" error will show both, which may make the error
easier to diagnose. Compared to alloc-then-free, this setting slightly increases
Valgrind's memory use as the block contains two references instead of one.
With alloc, only the allocation stack trace is recorded (and reported). With free,
only the deallocation stack trace is recorded (and reported). These values somewhat
decrease Valgrind's memory and cpu usage. They can be useful depending on the error
types you are searching for and the level of detail you need to analyse them. For
example, if you are only interested in memory leak errors, it is sufficient to record
the allocation stack traces.
With none, no stack traces are recorded for malloc and free operations. If your
program allocates a lot of blocks and/or allocates/frees from many different stack
traces, this can significantly decrease cpu and/or memory required. Of course, few
details will be reported for errors related to heap blocks.
Note that once a stack trace is recorded, Valgrind keeps the stack trace in memory
even if it is not referenced by any block. Some programs (for example, recursive
algorithms) can generate a huge number of stack traces. If Valgrind uses too much
memory in such circumstances, you can reduce the memory required with the options
--keep-stacktraces and/or by using a smaller value for the option --num-callers.
If you want to use --xtree-memory=full memory profiling (see Execution Trees), then
you cannot specify --keep-stacktraces=free or --keep-stacktraces=none.
--freelist-vol=<number> [default: 20000000]
When the client program releases memory using free (in C) or delete (C++), that memory
is not immediately made available for re-allocation. Instead, it is marked
inaccessible and placed in a queue of freed blocks. The purpose is to defer as long as
possible the point at which freed-up memory comes back into circulation. This
increases the chance that Memcheck will be able to detect invalid accesses to blocks
for some significant period of time after they have been freed.
This option specifies the maximum total size, in bytes, of the blocks in the queue.
The default value is twenty million bytes. Increasing this increases the total amount
of memory used by Memcheck but may detect invalid uses of freed blocks which would
otherwise go undetected.
--freelist-big-blocks=<number> [default: 1000000]
When making blocks from the queue of freed blocks available for re-allocation,
Memcheck will in priority re-circulate the blocks with a size greater or equal to
--freelist-big-blocks. This ensures that freeing big blocks (in particular freeing
blocks bigger than --freelist-vol) does not immediately lead to a re-circulation of
all (or a lot of) the small blocks in the free list. In other words, this option
increases the likelihood to discover dangling pointers for the "small" blocks, even
when big blocks are freed.
Setting a value of 0 means that all the blocks are re-circulated in a FIFO order.
--workaround-gcc296-bugs=<yes|no> [default: no]
When enabled, assume that reads and writes some small distance below the stack pointer
are due to bugs in GCC 2.96, and does not report them. The "small distance" is 256
bytes by default. Note that GCC 2.96 is the default compiler on some ancient Linux
distributions (RedHat 7.X) and so you may need to use this option. Do not use it if
you do not have to, as it can cause real errors to be overlooked. A better alternative
is to use a more recent GCC in which this bug is fixed.
You may also need to use this option when working with GCC 3.X or 4.X on 32-bit
PowerPC Linux. This is because GCC generates code which occasionally accesses below
the stack pointer, particularly for floating-point to/from integer conversions. This
is in violation of the 32-bit PowerPC ELF specification, which makes no provision for
locations below the stack pointer to be accessible.
This option is deprecated as of version 3.12 and may be removed from future versions.
You should instead use --ignore-range-below-sp to specify the exact range of offsets
below the stack pointer that should be ignored. A suitable equivalent is
--ignore-range-below-sp=1024-1.
--ignore-range-below-sp=<number>-<number>
This is a more general replacement for the deprecated --workaround-gcc296-bugs option.
When specified, it causes Memcheck not to report errors for accesses at the specified
offsets below the stack pointer. The two offsets must be positive decimal numbers and
-- somewhat counterintuitively -- the first one must be larger, in order to imply a
non-wraparound address range to ignore. For example, to ignore 4 byte accesses at 8192
bytes below the stack pointer, use --ignore-range-below-sp=8192-8189. Only one range
may be specified.
--show-mismatched-frees=<yes|no> [default: yes]
When enabled, Memcheck checks that heap blocks are deallocated using a function that
matches the allocating function. That is, it expects free to be used to deallocate
blocks allocated by malloc, delete for blocks allocated by new, and delete[] for
blocks allocated by new[]. If a mismatch is detected, an error is reported. This is in
general important because in some environments, freeing with a non-matching function
can cause crashes.
There is however a scenario where such mismatches cannot be avoided. That is when the
user provides implementations of new/new[] that call malloc and of delete/delete[]
that call free, and these functions are asymmetrically inlined. For example, imagine
that delete[] is inlined but new[] is not. The result is that Memcheck "sees" all
delete[] calls as direct calls to free, even when the program source contains no
mismatched calls.
This causes a lot of confusing and irrelevant error reports.
--show-mismatched-frees=no disables these checks. It is not generally advisable to
disable them, though, because you may miss real errors as a result.
--ignore-ranges=0xPP-0xQQ[,0xRR-0xSS]
Any ranges listed in this option (and multiple ranges can be specified, separated by
commas) will be ignored by Memcheck's addressability checking.
--malloc-fill=<hexnumber>
Fills blocks allocated by malloc, new, etc, but not by calloc, with the specified
byte. This can be useful when trying to shake out obscure memory corruption problems.
The allocated area is still regarded by Memcheck as undefined -- this option only
affects its contents. Note that --malloc-fill does not affect a block of memory when
it is used as argument to client requests VALGRIND_MEMPOOL_ALLOC or
VALGRIND_MALLOCLIKE_BLOCK.
--free-fill=<hexnumber>
Fills blocks freed by free, delete, etc, with the specified byte value. This can be
useful when trying to shake out obscure memory corruption problems. The freed area is
still regarded by Memcheck as not valid for access -- this option only affects its
contents. Note that --free-fill does not affect a block of memory when it is used as
argument to client requests VALGRIND_MEMPOOL_FREE or VALGRIND_FREELIKE_BLOCK.
CACHEGRIND OPTIONS
--cachegrind-out-file=<file>
Write the Cachegrind output file to file rather than to the default output file,
cachegrind.out.<pid>. The %p and %q format specifiers can be used to embed the process
ID and/or the contents of an environment variable in the name, as is the case for the
core option --log-file.
--cache-sim=no|yes [no]
Enables or disables collection of cache access and miss counts.
--branch-sim=no|yes [no]
Enables or disables collection of branch instruction and misprediction counts.
--I1=<size>,<associativity>,<line size>
Specify the size, associativity and line size of the level 1 instruction cache. Only
useful with --cache-sim=yes.
--D1=<size>,<associativity>,<line size>
Specify the size, associativity and line size of the level 1 data cache. Only useful
with --cache-sim=yes.
--LL=<size>,<associativity>,<line size>
Specify the size, associativity and line size of the last-level cache. Only useful
with --cache-sim=yes.
CALLGRIND OPTIONS
--callgrind-out-file=<file>
Write the profile data to file rather than to the default output file,
callgrind.out.<pid>. The %p and %q format specifiers can be used to embed the process
ID and/or the contents of an environment variable in the name, as is the case for the
core option --log-file. When multiple dumps are made, the file name is modified
further; see below.
--dump-line=<no|yes> [default: yes]
This specifies that event counting should be performed at source line granularity.
This allows source annotation for sources which are compiled with debug information
(-g).
--dump-instr=<no|yes> [default: no]
This specifies that event counting should be performed at per-instruction granularity.
This allows for assembly code annotation. Currently the results can only be displayed
by KCachegrind.
--compress-strings=<no|yes> [default: yes]
This option influences the output format of the profile data. It specifies whether
strings (file and function names) should be identified by numbers. This shrinks the
file, but makes it more difficult for humans to read (which is not recommended in any
case).
--compress-pos=<no|yes> [default: yes]
This option influences the output format of the profile data. It specifies whether
numerical positions are always specified as absolute values or are allowed to be
relative to previous numbers. This shrinks the file size.
--combine-dumps=<no|yes> [default: no]
When enabled, when multiple profile data parts are to be generated these parts are
appended to the same output file. Not recommended.
--dump-every-bb=<count> [default: 0, never]
Dump profile data every count basic blocks. Whether a dump is needed is only checked
when Valgrind's internal scheduler is run. Therefore, the minimum setting useful is
about 100000. The count is a 64-bit value to make long dump periods possible.
--dump-before=<function>
Dump when entering function.
--zero-before=<function>
Zero all costs when entering function.
--dump-after=<function>
Dump when leaving function.
--instr-atstart=<yes|no> [default: yes]
Specify if you want Callgrind to start simulation and profiling from the beginning of
the program. When set to no, Callgrind will not be able to collect any information,
including calls, but it will have at most a slowdown of around 4, which is the minimum
Valgrind overhead. Instrumentation can be interactively enabled via callgrind_control
-i on.
Note that the resulting call graph will most probably not contain main, but will
contain all the functions executed after instrumentation was enabled. Instrumentation
can also be programmatically enabled/disabled. See the Callgrind include file
callgrind.h for the macro you have to use in your source code.
For cache simulation, results will be less accurate when switching on instrumentation
later in the program run, as the simulator starts with an empty cache at that moment.
Switch on event collection later to cope with this error.
--collect-atstart=<yes|no> [default: yes]
Specify whether event collection is enabled at beginning of the profile run.
To only look at parts of your program, you have two possibilities:
1. Zero event counters before entering the program part you want to profile, and dump
the event counters to a file after leaving that program part.
2. Switch on/off collection state as needed to only see event counters happening
while inside of the program part you want to profile.
The second option can be used if the program part you want to profile is called many
times. Option 1, i.e. creating a lot of dumps is not practical here.
Collection state can be toggled at entry and exit of a given function with the option
--toggle-collect. If you use this option, collection state should be disabled at the
beginning. Note that the specification of --toggle-collect implicitly sets
--collect-state=no.
Collection state can be toggled also by inserting the client request
CALLGRIND_TOGGLE_COLLECT ; at the needed code positions.
--toggle-collect=<function>
Toggle collection on entry/exit of function.
--collect-jumps=<no|yes> [default: no]
This specifies whether information for (conditional) jumps should be collected. As
above, callgrind_annotate currently is not able to show you the data. You have to use
KCachegrind to get jump arrows in the annotated code.
--collect-systime=<no|yes|msec|usec|nsec> [default: no]
This specifies whether information for system call times should be collected.
The value no indicates to record no system call information.
The other values indicate to record the number of system calls done (sysCount event)
and the elapsed time (sysTime event) spent in system calls. The --collect-systime
value gives the unit used for sysTime : milli seconds, micro seconds or nano seconds.
With the value nsec, callgrind also records the cpu time spent during system calls
(sysCpuTime).
The value yes is a synonym of msec. The value nsec is not supported on Darwin.
--collect-bus=<no|yes> [default: no]
This specifies whether the number of global bus events executed should be collected.
The event type "Ge" is used for these events.
--cache-sim=<yes|no> [default: no]
Specify if you want to do full cache simulation. By default, only instruction read
accesses will be counted ("Ir"). With cache simulation, further event counters are
enabled: Cache misses on instruction reads ("I1mr"/"ILmr"), data read accesses ("Dr")
and related cache misses ("D1mr"/"DLmr"), data write accesses ("Dw") and related cache
misses ("D1mw"/"DLmw"). For more information, see Cachegrind: a cache and branch-
prediction profiler.
--branch-sim=<yes|no> [default: no]
Specify if you want to do branch prediction simulation. Further event counters are
enabled: Number of executed conditional branches and related predictor misses
("Bc"/"Bcm"), executed indirect jumps and related misses of the jump address predictor
("Bi"/"Bim").
HELGRIND OPTIONS
--free-is-write=no|yes [default: no]
When enabled (not the default), Helgrind treats freeing of heap memory as if the
memory was written immediately before the free. This exposes races where memory is
referenced by one thread, and freed by another, but there is no observable
synchronisation event to ensure that the reference happens before the free.
This functionality is new in Valgrind 3.7.0, and is regarded as experimental. It is
not enabled by default because its interaction with custom memory allocators is not
well understood at present. User feedback is welcomed.
--track-lockorders=no|yes [default: yes]
When enabled (the default), Helgrind performs lock order consistency checking. For
some buggy programs, the large number of lock order errors reported can become
annoying, particularly if you're only interested in race errors. You may therefore
find it helpful to disable lock order checking.
--history-level=none|approx|full [default: full]
--history-level=full (the default) causes Helgrind collects enough information about
"old" accesses that it can produce two stack traces in a race report -- both the stack
trace for the current access, and the trace for the older, conflicting access. To
limit memory usage, "old" accesses stack traces are limited to a maximum of
--history-backtrace-size entries (default 8) or to --num-callers value if this value
is smaller.
Collecting such information is expensive in both speed and memory, particularly for
programs that do many inter-thread synchronisation events (locks, unlocks, etc).
Without such information, it is more difficult to track down the root causes of races.
Nonetheless, you may not need it in situations where you just want to check for the
presence or absence of races, for example, when doing regression testing of a
previously race-free program.
--history-level=none is the opposite extreme. It causes Helgrind not to collect any
information about previous accesses. This can be dramatically faster than
--history-level=full.
--history-level=approx provides a compromise between these two extremes. It causes
Helgrind to show a full trace for the later access, and approximate information
regarding the earlier access. This approximate information consists of two stacks, and
the earlier access is guaranteed to have occurred somewhere between program points
denoted by the two stacks. This is not as useful as showing the exact stack for the
previous access (as --history-level=full does), but it is better than nothing, and it
is almost as fast as --history-level=none.
--history-backtrace-size=<number> [default: 8]
When --history-level=full is selected, --history-backtrace-size=number indicates how
many entries to record in "old" accesses stack traces.
--delta-stacktrace=no|yes [default: yes on linux amd64/x86]
This flag only has any effect at --history-level=full.
--delta-stacktrace configures the way Helgrind captures the stacktraces for the option
--history-level=full. Such a stacktrace is typically needed each time a new piece of
memory is read or written in a basic block of instructions.
--delta-stacktrace=no causes Helgrind to compute a full history stacktrace from the
unwind info each time a stacktrace is needed.
--delta-stacktrace=yes indicates to Helgrind to derive a new stacktrace from the
previous stacktrace, as long as there was no call instruction, no return instruction,
or any other instruction changing the call stack since the previous stacktrace was
captured. If no such instruction was executed, the new stacktrace can be derived from
the previous stacktrace by just changing the top frame to the current program counter.
This option can speed up Helgrind by 25% when using --history-level=full.
The following aspects have to be considered when using --delta-stacktrace=yes :
• In some cases (for example in a function prologue), the valgrind unwinder might
not properly unwind the stack, due to some limitations and/or due to wrong unwind
info. When using --delta-stacktrace=yes, the wrong stack trace captured in the
function prologue will be kept till the next call or return.
• On the other hand, --delta-stacktrace=yes sometimes helps to obtain a correct
stacktrace, for example when the unwind info allows a correct stacktrace to be
done in the beginning of the sequence, but not later on in the instruction
sequence.
• Determining which instructions are changing the callstack is partially based on
platform dependent heuristics, which have to be tuned/validated specifically for
the platform. Also, unwinding in a function prologue must be good enough to allow
using --delta-stacktrace=yes. Currently, the option --delta-stacktrace=yes has
been reasonably validated only on linux x86 32 bits and linux amd64 64 bits. For
more details about how to validate --delta-stacktrace=yes, see debug option
--hg-sanity-flags and the function check_cached_rcec_ok in libhb_core.c.
--conflict-cache-size=N [default: 1000000]
This flag only has any effect at --history-level=full.
Information about "old" conflicting accesses is stored in a cache of limited size,
with LRU-style management. This is necessary because it isn't practical to store a
stack trace for every single memory access made by the program. Historical information
on not recently accessed locations is periodically discarded, to free up space in the
cache.
This option controls the size of the cache, in terms of the number of different memory
addresses for which conflicting access information is stored. If you find that
Helgrind is showing race errors with only one stack instead of the expected two
stacks, try increasing this value.
The minimum value is 10,000 and the maximum is 30,000,000 (thirty times the default
value). Increasing the value by 1 increases Helgrind's memory requirement by very
roughly 100 bytes, so the maximum value will easily eat up three extra gigabytes or so
of memory.
--check-stack-refs=no|yes [default: yes]
By default Helgrind checks all data memory accesses made by your program. This flag
enables you to skip checking for accesses to thread stacks (local variables). This can
improve performance, but comes at the cost of missing races on stack-allocated data.
--ignore-thread-creation=<yes|no> [default: no]
Controls whether all activities during thread creation should be ignored. By default
enabled only on Solaris. Solaris provides higher throughput, parallelism and
scalability than other operating systems, at the cost of more fine-grained locking
activity. This means for example that when a thread is created under glibc, just one
big lock is used for all thread setup. Solaris libc uses several fine-grained locks
and the creator thread resumes its activities as soon as possible, leaving for example
stack and TLS setup sequence to the created thread. This situation confuses Helgrind
as it assumes there is some false ordering in place between creator and created
thread; and therefore many types of race conditions in the application would not be
reported. To prevent such false ordering, this command line option is set to yes by
default on Solaris. All activity (loads, stores, client requests) is therefore ignored
during:
• pthread_create() call in the creator thread
• thread creation phase (stack and TLS setup) in the created thread
Also new memory allocated during thread creation is untracked, that is race reporting
is suppressed there. DRD does the same thing implicitly. This is necessary because
Solaris libc caches many objects and reuses them for different threads and that
confuses Helgrind.
DRD OPTIONS
--check-stack-var=<yes|no> [default: no]
Controls whether DRD detects data races on stack variables. Verifying stack variables
is disabled by default because most programs do not share stack variables over
threads.
--exclusive-threshold=<n> [default: off]
Print an error message if any mutex or writer lock has been held longer than the time
specified in milliseconds. This option enables the detection of lock contention.
--join-list-vol=<n> [default: 10]
Data races that occur between a statement at the end of one thread and another thread
can be missed if memory access information is discarded immediately after a thread has
been joined. This option allows one to specify for how many joined threads memory
access information should be retained.
--first-race-only=<yes|no> [default: no]
Whether to report only the first data race that has been detected on a memory location
or all data races that have been detected on a memory location.
--free-is-write=<yes|no> [default: no]
Whether to report races between accessing memory and freeing memory. Enabling this
option may cause DRD to run slightly slower. Notes:
• Don't enable this option when using custom memory allocators that use the
VG_USERREQ__MALLOCLIKE_BLOCK and VG_USERREQ__FREELIKE_BLOCK because that would
result in false positives.
• Don't enable this option when using reference-counted objects because that will
result in false positives, even when that code has been annotated properly with
ANNOTATE_HAPPENS_BEFORE and ANNOTATE_HAPPENS_AFTER. See e.g. the output of the
following command for an example: valgrind --tool=drd --free-is-write=yes
drd/tests/annotate_smart_pointer.
--report-signal-unlocked=<yes|no> [default: yes]
Whether to report calls to pthread_cond_signal and pthread_cond_broadcast where the
mutex associated with the signal through pthread_cond_wait or
pthread_cond_timed_waitis not locked at the time the signal is sent. Sending a signal
without holding a lock on the associated mutex is a common programming error which can
cause subtle race conditions and unpredictable behavior. There exist some uncommon
synchronization patterns however where it is safe to send a signal without holding a
lock on the associated mutex.
--segment-merging=<yes|no> [default: yes]
Controls segment merging. Segment merging is an algorithm to limit memory usage of the
data race detection algorithm. Disabling segment merging may improve the accuracy of
the so-called 'other segments' displayed in race reports but can also trigger an out
of memory error.
--segment-merging-interval=<n> [default: 10]
Perform segment merging only after the specified number of new segments have been
created. This is an advanced configuration option that allows one to choose whether to
minimize DRD's memory usage by choosing a low value or to let DRD run faster by
choosing a slightly higher value. The optimal value for this parameter depends on the
program being analyzed. The default value works well for most programs.
--shared-threshold=<n> [default: off]
Print an error message if a reader lock has been held longer than the specified time
(in milliseconds). This option enables the detection of lock contention.
--show-confl-seg=<yes|no> [default: yes]
Show conflicting segments in race reports. Since this information can help to find the
cause of a data race, this option is enabled by default. Disabling this option makes
the output of DRD more compact.
--show-stack-usage=<yes|no> [default: no]
Print stack usage at thread exit time. When a program creates a large number of
threads it becomes important to limit the amount of virtual memory allocated for
thread stacks. This option makes it possible to observe how much stack memory has been
used by each thread of the client program. Note: the DRD tool itself allocates some
temporary data on the client thread stack. The space necessary for this temporary data
must be allocated by the client program when it allocates stack memory, but is not
included in stack usage reported by DRD.
--ignore-thread-creation=<yes|no> [default: no]
Controls whether all activities during thread creation should be ignored. By default
enabled only on Solaris. Solaris provides higher throughput, parallelism and
scalability than other operating systems, at the cost of more fine-grained locking
activity. This means for example that when a thread is created under glibc, just one
big lock is used for all thread setup. Solaris libc uses several fine-grained locks
and the creator thread resumes its activities as soon as possible, leaving for example
stack and TLS setup sequence to the created thread. This situation confuses DRD as it
assumes there is some false ordering in place between creator and created thread; and
therefore many types of race conditions in the application would not be reported. To
prevent such false ordering, this command line option is set to yes by default on
Solaris. All activity (loads, stores, client requests) is therefore ignored during:
• pthread_create() call in the creator thread
• thread creation phase (stack and TLS setup) in the created thread
--trace-addr=<address> [default: none]
Trace all load and store activity for the specified address. This option may be
specified more than once.
--ptrace-addr=<address> [default: none]
Trace all load and store activity for the specified address and keep doing that even
after the memory at that address has been freed and reallocated.
--trace-alloc=<yes|no> [default: no]
Trace all memory allocations and deallocations. May produce a huge amount of output.
--trace-barrier=<yes|no> [default: no]
Trace all barrier activity.
--trace-cond=<yes|no> [default: no]
Trace all condition variable activity.
--trace-fork-join=<yes|no> [default: no]
Trace all thread creation and all thread termination events.
--trace-hb=<yes|no> [default: no]
Trace execution of the ANNOTATE_HAPPENS_BEFORE(), ANNOTATE_HAPPENS_AFTER() and
ANNOTATE_HAPPENS_DONE() client requests.
--trace-mutex=<yes|no> [default: no]
Trace all mutex activity.
--trace-rwlock=<yes|no> [default: no]
Trace all reader-writer lock activity.
--trace-semaphore=<yes|no> [default: no]
Trace all semaphore activity.
MASSIF OPTIONS
--heap=<yes|no> [default: yes]
Specifies whether heap profiling should be done.
--heap-admin=<size> [default: 8]
If heap profiling is enabled, gives the number of administrative bytes per block to
use. This should be an estimate of the average, since it may vary. For example, the
allocator used by glibc on Linux requires somewhere between 4 to 15 bytes per block,
depending on various factors. That allocator also requires admin space for freed
blocks, but Massif cannot account for this.
--stacks=<yes|no> [default: no]
Specifies whether stack profiling should be done. This option slows Massif down
greatly, and so is off by default. Note that Massif assumes that the main stack has
size zero at start-up. This is not true, but doing otherwise accurately is difficult.
Furthermore, starting at zero better indicates the size of the part of the main stack
that a user program actually has control over.
--pages-as-heap=<yes|no> [default: no]
Tells Massif to profile memory at the page level rather than at the malloc'd block
level. See above for details.
--depth=<number> [default: 30]
Maximum depth of the allocation trees recorded for detailed snapshots. Increasing it
will make Massif run somewhat more slowly, use more memory, and produce bigger output
files.
--alloc-fn=<name>
Functions specified with this option will be treated as though they were a heap
allocation function such as malloc. This is useful for functions that are wrappers to
malloc or new, which can fill up the allocation trees with uninteresting information.
This option can be specified multiple times on the command line, to name multiple
functions.
Note that the named function will only be treated this way if it is the top entry in a
stack trace, or just below another function treated this way. For example, if you have
a function malloc1 that wraps malloc, and malloc2 that wraps malloc1, just specifying
--alloc-fn=malloc2 will have no effect. You need to specify --alloc-fn=malloc1 as
well. This is a little inconvenient, but the reason is that checking for allocation
functions is slow, and it saves a lot of time if Massif can stop looking through the
stack trace entries as soon as it finds one that doesn't match rather than having to
continue through all the entries.
Note that C++ names are demangled. Note also that overloaded C++ names must be written
in full. Single quotes may be necessary to prevent the shell from breaking them up.
For example:
--alloc-fn='operator new(unsigned, std::nothrow_t const&)'
--ignore-fn=<name>
Any direct heap allocation (i.e. a call to malloc, new, etc, or a call to a function
named by an --alloc-fn option) that occurs in a function specified by this option will
be ignored. This is mostly useful for testing purposes. This option can be specified
multiple times on the command line, to name multiple functions.
Any realloc of an ignored block will also be ignored, even if the realloc call does
not occur in an ignored function. This avoids the possibility of negative heap sizes
if ignored blocks are shrunk with realloc.
The rules for writing C++ function names are the same as for --alloc-fn above.
--threshold=<m.n> [default: 1.0]
The significance threshold for heap allocations, as a percentage of total memory size.
Allocation tree entries that account for less than this will be aggregated. Note that
this should be specified in tandem with ms_print's option of the same name.
--peak-inaccuracy=<m.n> [default: 1.0]
Massif does not necessarily record the actual global memory allocation peak; by
default it records a peak only when the global memory allocation size exceeds the
previous peak by at least 1.0%. This is because there can be many local allocation
peaks along the way, and doing a detailed snapshot for every one would be expensive
and wasteful, as all but one of them will be later discarded. This inaccuracy can be
changed (even to 0.0%) via this option, but Massif will run drastically slower as the
number approaches zero.
--time-unit=<i|ms|B> [default: i]
The time unit used for the profiling. There are three possibilities: instructions
executed (i), which is good for most cases; real (wallclock) time (ms, i.e.
milliseconds), which is sometimes useful; and bytes allocated/deallocated on the heap
and/or stack (B), which is useful for very short-run programs, and for testing
purposes, because it is the most reproducible across different machines.
--detailed-freq=<n> [default: 10]
Frequency of detailed snapshots. With --detailed-freq=1, every snapshot is detailed.
--max-snapshots=<n> [default: 100]
The maximum number of snapshots recorded. If set to N, for all programs except very
short-running ones, the final number of snapshots will be between N/2 and N.
--massif-out-file=<file> [default: massif.out.%p]
Write the profile data to file rather than to the default output file,
massif.out.<pid>. The %p and %q format specifiers can be used to embed the process ID
and/or the contents of an environment variable in the name, as is the case for the
core option --log-file.
BBV OPTIONS
--bb-out-file=<name> [default: bb.out.%p]
This option selects the name of the basic block vector file. The %p and %q format
specifiers can be used to embed the process ID and/or the contents of an environment
variable in the name, as is the case for the core option --log-file.
--pc-out-file=<name> [default: pc.out.%p]
This option selects the name of the PC file. This file holds program counter addresses
and function name info for the various basic blocks. This can be used in conjunction
with the basic block vector file to fast-forward via function names instead of just
instruction counts. The %p and %q format specifiers can be used to embed the process
ID and/or the contents of an environment variable in the name, as is the case for the
core option --log-file.
--interval-size=<number> [default: 100000000]
This option selects the size of the interval to use. The default is 100 million
instructions, which is a commonly used value. Other sizes can be used; smaller
intervals can help programs with finer-grained phases. However smaller interval size
can lead to accuracy issues due to warm-up effects (When fast-forwarding the various
architectural features will be un-initialized, and it will take some number of
instructions before they "warm up" to the state a full simulation would be at without
the fast-forwarding. Large interval sizes tend to mitigate this.)
--instr-count-only [default: no]
This option tells the tool to only display instruction count totals, and to not
generate the actual basic block vector file. This is useful for debugging, and for
gathering instruction count info without generating the large basic block vector
files.
LACKEY OPTIONS
--basic-counts=<no|yes> [default: yes]
When enabled, Lackey prints the following statistics and information about the
execution of the client program:
1. The number of calls to the function specified by the --fnname option (the default
is main). If the program has had its symbols stripped, the count will always be
zero.
2. The number of conditional branches encountered and the number and proportion of
those taken.
3. The number of superblocks entered and completed by the program. Note that due to
optimisations done by the JIT, this is not at all an accurate value.
4. The number of guest (x86, amd64, ppc, etc.) instructions and IR statements
executed. IR is Valgrind's RISC-like intermediate representation via which all
instrumentation is done.
5. Ratios between some of these counts.
6. The exit code of the client program.
--detailed-counts=<no|yes> [default: no]
When enabled, Lackey prints a table containing counts of loads, stores and ALU
operations, differentiated by their IR types. The IR types are identified by their IR
name ("I1", "I8", ... "I128", "F32", "F64", and "V128").
--trace-mem=<no|yes> [default: no]
When enabled, Lackey prints the size and address of almost every memory access made by
the program. See the comments at the top of the file lackey/lk_main.c for details
about the output format, how it works, and inaccuracies in the address trace. Note
that this option produces immense amounts of output.
--trace-superblocks=<no|yes> [default: no]
When enabled, Lackey prints out the address of every superblock (a single entry,
multiple exit, linear chunk of code) executed by the program. This is primarily of
interest to Valgrind developers. See the comments at the top of the file
lackey/lk_main.c for details about the output format. Note that this option produces
large amounts of output.
--fnname=<name> [default: main]
Changes the function for which calls are counted when --basic-counts=yes is specified.
DEBUGINFOD
Valgrind supports the downloading of debuginfo files via debuginfod, an HTTP server for
distributing ELF/DWARF debugging information. When a debuginfo file cannot be found
locally, Valgrind is able to query debuginfod servers for the file using the file's
build-id.
In order to use this feature debuginfod-find must be installed and the $DEBUGINFOD_URLS
environment variable must contain space-separated URLs of debuginfod servers. Valgrind
does not support debuginfod-find verbose output that is normally enabled with
$DEBUGINFOD_PROGRESS and $DEBUGINFOD_VERBOSE. These environment variables will be ignored.
This feature is supported on Linux only.
For more information regarding debuginfod, see Elfutils Debuginfod[1] .
SEE ALSO
cg_annotate(1), callgrind_annotate(1), callgrind_control(1), ms_print(1),
$INSTALL/share/doc/valgrind/html/index.html or
http://www.valgrind.org/docs/manual/index.html, Debugging your program using Valgrind's
gdbserver and GDB[2] vgdb[3], Valgrind monitor commands[4], The Commentary[5], Scheduling
and Multi-Thread Performance[6], Cachegrind: a cache and branch-prediction profiler[7].
Execution Trees[8]
AUTHOR
See the AUTHORS file in the valgrind distribution for a comprehensive list of authors.
This manpage was written by Andres Roldan <aroldan@debian.org> and the Valgrind
developers.
NOTES
1. Elfutils Debuginfod
https://sourceware.org/elfutils/Debuginfod.html
2. Debugging your program using Valgrind's gdbserver and GDB
http://www.valgrind.org/docs/manual/manual-core-adv.html#manual-core-adv.gdbserver
3. vgdb
http://www.valgrind.org/docs/manual/manual-core-adv.html#manual-core-adv.vgdb
4. Valgrind monitor commands
http://www.valgrind.org/docs/manual/manual-core-adv.html#manual-core-adv.valgrind-monitor-commands
5. The Commentary
http://www.valgrind.org/docs/manual/manual-core.html#manual-core.comment
6. Scheduling and Multi-Thread Performance
http://www.valgrind.org/docs/manual/manual-core.html#manual-core.pthreads_perf_sched
7. Cachegrind: a cache and branch-prediction profiler
http://www.valgrind.org/docs/manual/cg-manual.html
8. Execution Trees
http://www.valgrind.org/docs/manual/manual-core.html#manual-core.xtree