Ubuntu Manpage: dwz - DWARF optimization and duplicate removal tool

NAME

       dwz - DWARF optimization and duplicate removal tool

SYNOPSIS

       dwz [OPTION...] [FILES]

DESCRIPTION

       dwz  is  a  program that attempts to optimize DWARF debugging information contained in ELF
       shared  libraries  and  ELF  executables  for  size,  by   replacing   DWARF   information
       representation  with  equivalent smaller representation where possible and by reducing the
       amount of  duplication  using  techniques  from  DWARF  standard  appendix  E  -  creating
       DW_TAG_partial_unit   compilation   units  (CUs)  for  duplicated  information  and  using
       DW_TAG_imported_unit to import it into each CU that needs it.

       The tool handles DWARF 32-bit format debugging sections of  versions  2,  3,  4,  most  of
       version  5 and GNU extensions on top of those.  It is strongly recommended to use at least
       DWARF 3, but using DWARF 4 or higher will work much better.

       While most of DWARF  5  is  supported  dwz  doesn't  yet  generate  spec  compliant  DWARF
       Supplementary  Object  Files (DWARF 5, section 7.3.6) unless the --dwarf-5 option is used.
       Instead of a .debug_sup section it will generate by default a  .gnu_debugaltlink  section.
       And   it   will   use   the   DW_FORM_GNU_strp_alt  and  DW_FORM_GNU_reg_alt,  instead  of
       DW_FORM_strp_sup and DW_FORM_ref_sup to keep compatibility with existing DWARF consumers.

       DWARF 4 .debug_types are supported,  but  DWARF  5  DW_UT_type  units  are  not.  Likewise
       .gdb_index is supported, but the DWARF 5 .debug_names is not. Also some forms and sections
       that  are  only  emitted  by  GCC  when   generating   Split   DWARF,   DW_FORM_strx   and
       .debug_str_offsets, DW_FORM_addrx and .debug_addr, DW_FORM_rnglistx and DW_FORM_loclistsx,
       are not supported yet.

       The tool has two main modes of operation, without the -m option it  attempts  to  optimize
       DWARF   debugging  information  in  each  given  object  (executable  or  shared  library)
       individually, with the -m option it afterwards attempts to optimize even  more  by  moving
       DWARF  debugging  information entries (DIEs), strings and macro descriptions duplicated in
       more than one object into a newly created ELF ET_REL object whose filename is given as  -m
       option  argument.  The debug sections in the executables and shared libraries specified on
       the command line are then modified again, referring to the entities in the  newly  created
       object.

OPTIONS

-m FILE --multifile FILE
Multifile mode. After processing all named executables and shared libraries,
attempt to create ELF object FILE and put debugging information duplicated in more
than one object there, afterwards optimize each named executable or shared library
even further if possible.

-h --hardlink
Look for executables or shared libraries hardlinked together, instead of rewriting
them individually rewrite just one of them and hardlink the rest to the first one
again.

-M NAME --multifile-name NAME
Specify the name of the common file that should be put into the .gnu_debugaltlink
section alongside with its build ID. By default dwz puts there the argument of the
-m option.

-r --relative
Specify that the name of the common file to be put into the .gnu_debugaltlink
section is supposed to be relative path from the directory containing the
executable or shared library to the file named in the argument of the -m option.
Either -M or -r option can be specified, but not both.

-q --quiet
Silence up some of the most common messages.

-o FILE --output FILE
This option instructs dwz not to overwrite the specified file, but instead store
the new content into FILE. Nothing is written if dwz exits with non-zero exit
code. Can be used only with a single executable or shared library (if there are no
arguments at all, a.out is assumed).

-l <COUNT|none> --low-mem-die-limit <COUNT|none>
Handle executables or shared libraries containing more than COUNT debugging
information entries in their .debug_info section using a slower and more memory
usage friendly mode and don't attempt to optimize that object in multifile mode.
The default is 10 million DIEs. There is a risk that for very large amounts of
debugging information in a single shared library or executable there might not be
enough memory (especially when dwz tool is 32-bit binary, it might run out of
available virtual address space even sooner). Specifying none as argument disables
the limit.

-L <COUNT|none> --max-die-limit <COUNT|none>
Don't attempt to optimize executables or shared libraries containing more than
COUNT DIEs at all. The default is 50 million DIEs. Specifying none as argument
disables the limit.

-5 --dwarf-5
Emit standard DWARF 5 Supplementary Object Files with .debug_sup and corresponding
forms, instead of the GNU extension .gnu_debugaltlink and corresponding forms.

--odr / --no-odr
Experimental. Enable/disable One-Definition-Rule optimization for C++ compilation
units. This optimization causes struct/union/class DIEs with the same name to be
considered equal. This has the effect that DIEs referring to distinct DIEs
representing the same type (like f.i. pointer type DIEs) are considered equal, and
may be deduplicated. The status of this optimization is experimental. It's
disabled in low-mem mode. Disabled by default.

--odr-mode=<basic|link>
Set the One-Definition-Rule optimization aggressiveness: basic or link. When using
the link setting, the optimization will attempt to replace declarations of a
struct/union/class with a corresponding definition. When using the basic setting,
that part of the optimization is disabled. In normal operation, the link setting
should be used. The basic setting is provided only as fallback in case of problems
with the link setting. Set to link by default.

--import-optimize / --no-import-optimize
Enable/disable optimization that reduces the number of DW_TAG_imported_unit DIEs
generated to import the partial units created by dwz. Disabling the optimization
can be used to work around problems in the optimization, or to make it easier to
observe which CU imports which PU. Enabled by default.

-? --help
Print short help and exit.

-v --version
Print version number and short licensing notice and exit.

ARGUMENTS

       Command-line  arguments  should  be the executables, shared libraries or their stripped to
       file separate debug information objects.

EXAMPLES

              $ dwz -m .dwz/foobar-1.2.debug -rh \
                bin/foo.debug bin/foo2.debug foo/lib/libbar.so.debug
       will attempt to  optimize  debugging  information  in  bin/foo.debug,  bin/foo2.debug  and
       lib/libbar.so.debug (by modifying the files in place) and when beneficial also will create
       .dwz/foobar-1.2.debug file.  .gnu_debugaltlink section in the first two files  will  refer
       to  ../.dwz/foobar-1.2.debug and in the last file to ../../.dwz/foobar-1.2.debug.  If e.g.
       bin/foo.debug  and  bin/foo2.debug  were  hardlinked  together  initially,  they  will  be
       hardlinked  again  and for multifile optimizations considered just as a single file rather
       than two.
              $ dwz -o foo.dwz foo
       will not modify foo but instead store the ELF object with optimized debugging  information
       if successful into foo.dwz file it creates.
              $ dwz *.debug foo/*.debug
       will  attempt  to  optimize  debugging  information  in  *.debug  and  foo/*.debug  files,
       optimizing each file individually in place.
              $ dwz
       is equivalent to dwz a.out command.

AUTHORS

       Jakub  Jelinek  <jakub@redhat.com>,  Tom  de  Vries  <tdevries@suse.de>,   Mark   Wielaard
       <mark@klomp.org>

BUGS

       Use   the   Bugzilla   link   of   the   project   web   page   or   our   mailing   list.
       https://sourceware.org/dwz/, <dwz@sourceware.org>.

                                           15 Feb 2021                                     dwz(1)