5.3 Skipping Over Functions and Files

The program you are debugging may contain some functions which are uninteresting to debug. The skip command lets you tell GDB to skip a function, all functions in a file or a particular function in a particular file when stepping.

For example, consider the following C function:

101     int func()
102     {
103         foo(boring());
104         bar(boring());
105     }

Suppose you wish to step into the functions foo and bar, but you are not interested in stepping through boring. If you run step at line 103, you’ll enter boring(), but if you run next, you’ll step over both foo and boring!

One solution is to step into boring and use the finish command to immediately exit it. But this can become tedious if boring is called from many places.

A more flexible solution is to execute skip boring. This instructs GDB never to step into boring. Now when you execute step at line 103, you’ll step over boring and directly into foo.

Functions may be skipped by providing either a function name, linespec (see Specify Location), regular expression that matches the function’s name, file name or a glob-style pattern that matches the file name.

On Posix systems the form of the regular expression is “Extended Regular Expressions”. See for example ‘man 7 regex’ on GNU/Linux systems. On non-Posix systems the form of the regular expression is whatever is provided by the regcomp function of the underlying system. See for example ‘man 7 glob’ on GNU/Linux systems for a description of glob-style patterns.

skip [options]

The basic form of the skip command takes zero or more options that specify what to skip. The options argument is any useful combination of the following:

-file file

-fi file

Functions in file will be skipped over when stepping.

-gfile file-glob-pattern

-gfi file-glob-pattern

Functions in files matching file-glob-pattern will be skipped over when stepping.

(gdb) skip -gfi utils/*.c

-function linespec

-fu linespec

Functions named by linespec or the function containing the line named by linespec will be skipped over when stepping. See Specify Location.

-rfunction regexp

-rfu regexp

Functions whose name matches regexp will be skipped over when stepping.

This form is useful for complex function names. For example, there is generally no need to step into C++ std::string constructors or destructors. Plus with C++ templates it can be hard to write out the full name of the function, and often it doesn’t matter what the template arguments are. Specifying the function to be skipped as a regular expression makes this easier.

(gdb) skip -rfu ^std::(allocator|basic_string)<.*>::~?\1 *\(

If you want to skip every templated C++ constructor and destructor in the std namespace you can do:

(gdb) skip -rfu ^std::([a-zA-z0-9_]+)<.*>::~?\1 *\(

If no options are specified, the function you’re currently debugging will be skipped.

skip function [linespec]

After running this command, the function named by linespec or the function containing the line named by linespec will be skipped over when stepping. See Specify Location.

If you do not specify linespec, the function you’re currently debugging will be skipped.

(If you have a function called file that you want to skip, use skip function file.)

skip file [filename]

After running this command, any function whose source lives in filename will be skipped over when stepping.

(gdb) skip file boring.c
File boring.c will be skipped when stepping.

If you do not specify filename, functions whose source lives in the file you’re currently debugging will be skipped.

Skips can be listed, deleted, disabled, and enabled, much like breakpoints. These are the commands for managing your list of skips:

info skip [range]

Print details about the specified skip(s). If range is not specified, print a table with details about all functions and files marked for skipping. info skip prints the following information about each skip:

Identifier

A number identifying this skip.

Enabled or Disabled

Enabled skips are marked with ‘y’. Disabled skips are marked with ‘n’.

Glob

If the file name is a ‘glob’ pattern this is ‘y’. Otherwise it is ‘n’.

File

The name or ‘glob’ pattern of the file to be skipped. If no file is specified this is ‘<none>’.

RE

If the function name is a ‘regular expression’ this is ‘y’. Otherwise it is ‘n’.

Function

The name or regular expression of the function to skip. If no function is specified this is ‘<none>’.

skip delete [range]

Delete the specified skip(s). If range is not specified, delete all skips.

skip enable [range]

Enable the specified skip(s). If range is not specified, enable all skips.

skip disable [range]

Disable the specified skip(s). If range is not specified, disable all skips.

set debug skip [on|off]

Set whether to print the debug output about skipping files and functions.

show debug skip

Show whether the debug output about skipping files and functions is printed.