\input texinfo @c -*-texinfo-*-
@setfilename gprof.info
-@c Copyright 1988, 1992, 1993, 1998, 1999, 2000, 2001
+@c Copyright 1988, 1992, 1993, 1998, 1999, 2000, 2001, 2003
@c Free Software Foundation, Inc.
@settitle GNU gprof
@setchapternewpage odd
This file documents the gprof profiler of the GNU system.
@c man begin COPYRIGHT
-Copyright (C) 1988, 92, 97, 98, 99, 2000, 2001 Free Software Foundation, Inc.
+Copyright (C) 1988, 92, 97, 98, 99, 2000, 2001, 2003 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1
can use it to determine which parts of a program are taking most of the
execution time. We assume that you know how to write, compile, and
execute programs. @sc{gnu} @code{gprof} was written by Jay Fenlason.
+Eric S. Raymond made some minor corrections and additions in 2003.
@vskip 0pt plus 1filll
-Copyright @copyright{} 1988, 92, 97, 98, 99, 2000 Free Software Foundation, Inc.
+Copyright @copyright{} 1988, 92, 97, 98, 99, 2000, 2003 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1
cc -o myprog myprog.c utils.c -g -pg
@end example
+Note: The @samp{-pg} option must be part of your compilation options
+as well as your link options. If it is not then no call-graph data
+will be gathered and when you run @code{gprof} you will get an error
+message like this:
+
+@example
+gprof: gmon.out file is missing call-graph data
+@end example
+
+If you add the @samp{-Q} switch to suppress the printing of the call
+graph data you will still be able to see the time samples:
+
+@example
+Flat profile:
+
+Each sample counts as 0.01 seconds.
+ % cumulative self self total
+ time seconds seconds calls Ts/call Ts/call name
+ 44.12 0.07 0.07 zazLoop
+ 35.29 0.14 0.06 main
+ 20.59 0.17 0.04 bazMillion
+
+ % the percentage of the total running time of the
+@end example
+
If you run the linker @code{ld} directly instead of through a compiler
such as @code{cc}, you may have to specify a profiling startup file
@file{gcrt0.o} as the first input file instead of the usual startup
that match program addresses to source code lines.
@xref{Line-by-line}.
-In addition to the @samp{-pg} and @samp{-g} options,
-you may also wish to specify the @samp{-a} option when compiling.
-This will instrument
-the program to perform basic-block counting. As the program runs,
+In addition to the @samp{-pg} and @samp{-g} options, older versions of
+GCC required you to specify the @samp{-a} option when compiling in
+order to instrument it to perform basic-block counting. Newer
+versions do not require this option and will not accept it;
+basic-block counting is always enabled when @samp{-pg} is on.
+
+When basic-block counting is enabled, as the program runs
it will count how many times it executed each branch of each @samp{if}
statement, each iteration of each @samp{do} loop, etc. This will
enable @code{gprof} to construct an annotated source code
listing showing how many times each line of code was executed.
+It also worth noting that GCC supports a different profiling method
+which is enabled by the @samp{-fprofile-arcs}, @samp{-ftest-coverage}
+and @samp{-fprofile-values} switches. These switches do not produce
+data which is useful to @code{gprof} however, so they are not
+discussed further here. There is also the
+@samp{-finstrument-functions} switch which will cause GCC to insert
+calls to special user supplied instrumentation routines at the entry
+and exit of every function in their program. This can be used to
+implement an alternative profiling scheme.
+
@node Executing
@chapter Executing the Program
just before exiting. If there is already a file called @file{gmon.out},
its contents are overwritten. There is currently no way to tell the
program to write the profile data under a different name, but you can rename
-the file afterward if you are concerned that it may be overwritten.
+the file afterwards if you are concerned that it may be overwritten.
In order to write the @file{gmon.out} file properly, your program must exit
normally: by returning from @code{main} or by calling @code{exit}. Calling
@section Estimating @code{children} Times
Some of the figures in the call graph are estimates---for example, the
-@code{children} time values and all the the time figures in caller and
+@code{children} time values and all the time figures in caller and
subroutine lines.
There is no direct information about these measurements in the profile
@chapter Answers to Common Questions
@table @asis
+@item How can I get more exact information about hot spots in my program?
+
+Looking at the per-line call counts only tells part of the story.
+Because @code{gprof} can only report call times and counts by function,
+the best way to get finer-grained information on where the program
+is spending its time is to re-factor large functions into sequences
+of calls to smaller ones. Beware however that this can introduce
+artifical hot spots since compiling with @samp{-pg} adds a significant
+overhead to function calls. An alternative solution is to use a
+non-intrusive profiler, e.g.@: oprofile.
+
@item How do I find which lines in my program were executed the most times?
Compile your program with basic-block counting enabled, run it, then
projects / deliverable / binutils-gdb.git / blobdiff