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NAME
nm — write the name list of an object file (DEVELOPMENT)
SYNOPSIS
nm [-APv] [-g|-u] [-t format] file...
nm [-APv] [-efox] [-g|-u] [-t format] file...
DESCRIPTION
The nm utility shall display symbolic information appearing in the object file, executable
file, or object-file library named by file. If no symbolic information is available for a
valid input file, the nm utility shall report that fact, but not consider it an error
condition.
The default base used when numeric values are written is unspecified. On XSI-conformant
systems, it shall be decimal if the -P option is not specified.
OPTIONS
The nm utility shall conform to the Base Definitions volume of POSIX.1‐2017, Section 12.2,
Utility Syntax Guidelines.
The following options shall be supported:
-A Write the full pathname or library name of an object on each line.
-e Write only external (global) and static symbol information.
-f Produce full output. Write redundant symbols (.text, .data, and .bss), normally
suppressed.
-g Write only external (global) symbol information.
-o Write numeric values in octal (equivalent to -t o).
-P Write information in a portable output format, as specified in the STDOUT
section.
-t format Write each numeric value in the specified format. The format shall be dependent
on the single character used as the format option-argument:
d decimal (default if -P is not specified).
o octal.
x hexadecimal (default if -P is specified).
-u Write only undefined symbols.
-v Sort output by value instead of by symbol name.
-x Write numeric values in hexadecimal (equivalent to -t x).
OPERANDS
The following operand shall be supported:
file A pathname of an object file, executable file, or object-file library.
STDIN
See the INPUT FILES section.
INPUT FILES
The input file shall be an object file, an object-file library whose format is the same as
those produced by the ar utility for link editing, or an executable file. The nm utility
may accept additional implementation-defined object library formats for the input file.
ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of nm:
LANG Provide a default value for the internationalization variables that are unset or
null. (See the Base Definitions volume of POSIX.1‐2017, Section 8.2,
Internationalization Variables for the precedence of internationalization
variables used to determine the values of locale categories.)
LC_ALL If set to a non-empty string value, override the values of all the other
internationalization variables.
LC_COLLATE
Determine the locale for character collation information for the symbol-name and
symbol-value collation sequences.
LC_CTYPE Determine the locale for the interpretation of sequences of bytes of text data
as characters (for example, single-byte as opposed to multi-byte characters in
arguments).
LC_MESSAGES
Determine the locale that should be used to affect the format and contents of
diagnostic messages written to standard error.
NLSPATH Determine the location of message catalogs for the processing of LC_MESSAGES.
ASYNCHRONOUS EVENTS
Default.
STDOUT
If symbolic information is present in the input files, then for each file or for each
member of an archive, the nm utility shall write the following information to standard
output. By default, the format is unspecified, but the output shall be sorted by symbol
name according to the collation sequence in the current locale.
* Library or object name, if -A is specified
* Symbol name
* Symbol type, which shall either be one of the following single characters or an
implementation-defined type represented by a single character:
A Global absolute symbol.
a Local absolute symbol.
B Global ``bss'' (that is, uninitialized data space) symbol.
b Local bss symbol.
D Global data symbol.
d Local data symbol.
T Global text symbol.
t Local text symbol.
U Undefined symbol.
* Value of the symbol
* The size associated with the symbol, if applicable
This information may be supplemented by additional information specific to the
implementation.
If the -P option is specified, the previous information shall be displayed using the
following portable format. The three versions differ depending on whether -t d, -t o, or
-t x was specified, respectively:
"%s%s %s %d %d\n", <library/object name>, <name>, <type>,
<value>, <size>
"%s%s %s %o %o\n", <library/object name>, <name>, <type>,
<value>, <size>
"%s%s %s %x %x\n", <library/object name>, <name>, <type>,
<value>, <size>
where <library/object name> shall be formatted as follows:
* If -A is not specified, <library/object name> shall be an empty string.
* If -A is specified and the corresponding file operand does not name a library:
"%s: ", <file>
* If -A is specified and the corresponding file operand names a library. In this case,
<object file> shall name the object file in the library containing the symbol being
described:
"%s[%s]: ", <file>, <object file>
If -A is not specified, then if more than one file operand is specified or if only one
file operand is specified and it names a library, nm shall write a line identifying the
object containing the following symbols before the lines containing those symbols, in the
form:
* If the corresponding file operand does not name a library:
"%s:\n", <file>
* If the corresponding file operand names a library; in this case, <object file> shall
be the name of the file in the library containing the following symbols:
"%s[%s]:\n", <file>, <object file>
If -P is specified, but -t is not, the format shall be as if -t x had been specified.
STDERR
The standard error shall be used only for diagnostic messages.
OUTPUT FILES
None.
EXTENDED DESCRIPTION
None.
EXIT STATUS
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred.
CONSEQUENCES OF ERRORS
Default.
The following sections are informative.
APPLICATION USAGE
Mechanisms for dynamic linking make this utility less meaningful when applied to an
executable file because a dynamically linked executable may omit numerous library routines
that would be found in a statically linked executable.
EXAMPLES
None.
RATIONALE
Historical implementations of nm have used different bases for numeric output and supplied
different default types of symbols that were reported. The -t format option, similar to
that used in od and strings, can be used to specify the numeric base; -g and -u can be
used to restrict the amount of output or the types of symbols included in the output.
The compromise of using -t format versus using -d, -o, and other similar options was
necessary because of differences in the meaning of -o between implementations. The -o
option from BSD has been provided here as -A to avoid confusion with the -o from System V
(which has been provided here as -t and as -o on XSI-conformant systems).
The option list was significantly reduced from that provided by historical
implementations.
The nm description is a subset of both the System V and BSD nm utilities with no specified
default output.
It was recognized that mechanisms for dynamic linking make this utility less meaningful
when applied to an executable file (because a dynamically linked executable file may omit
numerous library routines that would be found in a statically linked executable file), but
the value of nm during software development was judged to outweigh other limitations.
The default output format of nm is not specified because of differences in historical
implementations. The -P option was added to allow some type of portable output format.
After a comparison of the different formats used in SunOS, BSD, SVR3, and SVR4, it was
decided to create one that did not match the current format of any of these four systems.
The format devised is easy to parse by humans, easy to parse in shell scripts, and does
not need to vary depending on locale (because no English descriptions are included). All
of the systems currently have the information available to use this format.
The format given in nm STDOUT uses <space> characters between the fields, which may be any
number of <blank> characters required to align the columns. The single-character types
were selected to match historical practice, and the requirement that implementation
additions also be single characters made parsing the information easier for shell scripts.
FUTURE DIRECTIONS
None.
SEE ALSO
ar, c99
The Base Definitions volume of POSIX.1‐2017, Chapter 8, Environment Variables, Section
12.2, Utility Syntax Guidelines
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1-2017, Standard for Information Technology -- Portable Operating System Interface
(POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by
the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and The Open Group
Standard, the original IEEE and The Open Group Standard is the referee document. The
original Standard can be obtained online at http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page are most likely to have
been introduced during the conversion of the source files to man page format. To report
such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .