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diff --git a/gprof/ChangeLog b/gprof/ChangeLog index 19f2200..18a5396 100644 --- a/gprof/ChangeLog +++ b/gprof/ChangeLog @@ -1,5 +1,8 @@ Tue Feb 3 14:25:25 1998 Brent Baccala <baccala@freesoft.org> + * gprof.texi: Extensive additions to document all arguments and + output formats. + * symtab.c (symtab_finalize): Prefer function symbols over line symbols. (dbg_sym_lookup): Correct debugging messages. diff --git a/gprof/gprof.texi b/gprof/gprof.texi index 0114307..4c22c9a 100644 --- a/gprof/gprof.texi +++ b/gprof/gprof.texi @@ -16,7 +16,7 @@ END-INFO-DIR-ENTRY @ifinfo This file documents the gprof profiler of the GNU system. -Copyright (C) 1988, 1992 Free Software Foundation, Inc. +Copyright (C) 1988, 1992, 1997, 1998 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice @@ -53,10 +53,11 @@ 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. -This manual was edited January 1993 by Jeffrey Osier. +This manual was edited January 1993 by Jeffrey Osier +and updated September 1997 by Brent Baccala. @vskip 0pt plus 1filll -Copyright @copyright{} 1988, 1992 Free Software Foundation, Inc. +Copyright @copyright{} 1988, 1992, 1997, 1998 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice @@ -88,37 +89,26 @@ 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. -This manual was updated January 1993. +This manual was updated August 1997 by Brent Baccala. @menu -* Why:: What profiling means, and why it is useful. -* Compiling:: How to compile your program for profiling. -* Executing:: How to execute your program to generate the - profile data file @file{gmon.out}. -* Invoking:: How to run @code{gprof}, and how to specify - options for it. +* Introduction:: What profiling means, and why it is useful. -* Flat Profile:: The flat profile shows how much time was spent - executing directly in each function. -* Call Graph:: The call graph shows which functions called which - others, and how much time each function used - when its subroutine calls are included. - -* Implementation:: How the profile data is recorded and written. -* Sampling Error:: Statistical margins of error. - How to accumulate data from several runs - to make it more accurate. +* Compiling:: How to compile your program for profiling. +* Executing:: Executing your program to generate profile data +* Invoking:: How to run @code{gprof}, and its options -* Assumptions:: Some of @code{gprof}'s measurements are based - on assumptions about your program - that could be very wrong. +* Output:: Interpreting @code{gprof}'s output -* Incompatibilities:: (between GNU @code{gprof} and Unix @code{gprof}.) +* Inaccuracy:: Potential problems you should be aware of +* How do I?:: Answers to common questions +* Incompatibilities:: (between @sc{gnu} @code{gprof} and Unix @code{gprof}.) +* Details:: Details of how profiling is done @end menu @end ifinfo -@node Why -@chapter Why Profile +@node Introduction +@chapter Introduction to Profiling Profiling allows you to learn where your program spent its time and which functions called which other functions while it was executing. This @@ -153,21 +143,27 @@ You must run @code{gprof} to analyze the profile data. The next three chapters explain these steps in greater detail. -The result of the analysis is a file containing two tables, the -@dfn{flat profile} and the @dfn{call graph} (plus blurbs which briefly -explain the contents of these tables). +Several forms of output are available from the analysis. -The flat profile shows how much time your program spent in each function, +The @dfn{flat profile} shows how much time your program spent in each function, and how many times that function was called. If you simply want to know which functions burn most of the cycles, it is stated concisely here. @xref{Flat Profile}. -The call graph shows, for each function, which functions called it, which +The @dfn{call graph} shows, for each function, which functions called it, which other functions it called, and how many times. There is also an estimate of how much time was spent in the subroutines of each function. This can suggest places where you might try to eliminate function calls that use a lot of time. @xref{Call Graph}. +The @dfn{annotated source} listing is a copy of the program's +source code, labeled with the number of times each line of the +program was executed. @xref{Annotated Source}. + +To better understand how profiling works, you may wish to read +a description of its implementation. +@xref{Implementation}. + @node Compiling @chapter Compiling a Program for Profiling @@ -195,10 +191,10 @@ cc -o myprog myprog.c utils.c -g -pg @end example If you run the linker @code{ld} directly instead of through a compiler -such as @code{cc}, you must specify the profiling startup file -@file{/lib/gcrt0.o} as the first input file instead of the usual startup -file @file{/lib/crt0.o}. In addition, you would probably want to -specify the profiling C library, @file{/usr/lib/libc_p.a}, by writing +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 +file @file{crt0.o}. In addition, you would probably want to +specify the profiling C library, @file{libc_p.a}, by writing @samp{-lc_p} instead of the usual @samp{-lc}. This is not absolutely necessary, but doing this gives you number-of-calls information for standard library functions such as @code{read} and @code{open}. For @@ -217,8 +213,23 @@ will not affect the flat profile (except that the @code{calls} field for the functions will be blank), but will greatly reduce the usefulness of the call graph. +If you wish to perform line-by-line profiling, +you will also need to specify the @samp{-g} option, +instructing the compiler to insert debugging symbols into the program +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, +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. + @node Executing -@chapter Executing the Program to Generate Profile Data +@chapter Executing the Program Once the program is compiled for profiling, you must run it in order to generate the information that @code{gprof} needs. Simply run the program @@ -234,7 +245,7 @@ the particular input you use. For example, if the first command you give to your program is to quit, the profile data will show the time used in initialization and in cleanup, but not much else. -You program will write the profile data into a file called @file{gmon.out} +Your program will write the profile data into a file called @file{gmon.out} 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 @@ -249,10 +260,16 @@ The @file{gmon.out} file is written in the program's @emph{current working directory} at the time it exits. This means that if your program calls @code{chdir}, the @file{gmon.out} file will be left in the last directory your program @code{chdir}'d to. If you don't have permission to write in -this directory, the file is not written. You may get a confusing error -message if this happens. (We have not yet replaced the part of Unix -responsible for this; when we do, we will make the error message -comprehensible.) +this directory, the file is not written, and you will get an error message. + +Older versions of the @sc{gnu} profiling library may also write a file +called @file{bb.out}. This file, if present, contains an human-readable +listing of the basic-block execution counts. Unfortunately, the +appearance of a human-readable @file{bb.out} means the basic-block +counts didn't get written into @file{gmon.out}. +The Perl script @code{bbconv.pl}, included with the @code{gprof} +source distribution, will convert a @file{bb.out} file into +a format readable by @code{gprof}. @node Invoking @chapter @code{gprof} Command Summary @@ -280,11 +297,195 @@ You can give more than one profile data file by entering all their names after the executable file name; then the statistics in all the data files are summed together. -The following options may be used to selectively include or exclude -functions in the output: +The order of these options does not matter. + +@menu +* Output Options:: Controlling @code{gprof}'s output style +* Analysis Options:: Controlling how @code{gprof} analyses its data +* Miscellaneous Options:: +* Depricated Options:: Options you no longer need to use, but which + have been retained for compatibility +* Symspecs:: Specifying functions to include or exclude +@end menu + +@node Output Options,Analysis Options,,Invoking +@section Output Options + +These options specify which of several output formats +@code{gprof} should produce. + +Many of these options take an optional @dfn{symspec} to specify +functions to be included or excluded. These options can be +specified multiple times, with different symspecs, to include +or exclude sets of symbols. @xref{Symspecs}. + +Specifying any of these options overrides the default (@samp{-p -q}), +which prints a flat profile and call graph analysis +for all functions. @table @code + +@item -A[@var{symspec}] +@itemx --annotated-source[=@var{symspec}] +The @samp{-A} option causes @code{gprof} to print annotated source code. +If @var{symspec} is specified, print output only for matching symbols. +@xref{Annotated Source}. + +@item -b +@itemx --brief +If the @samp{-b} option is given, @code{gprof} doesn't print the +verbose blurbs that try to explain the meaning of all of the fields in +the tables. This is useful if you intend to print out the output, or +are tired of seeing the blurbs. + +@item -C[@var{symspec}] +@itemx --exec-counts[=@var{symspec}] +The @samp{-C} option causes @code{gprof} to +print a tally of functions and the number of times each was called. +If @var{symspec} is specified, print tally only for matching symbols. + +If the profile data file contains basic-block count records, specifing +the @samp{-l} option, along with @samp{-C}, will cause basic-block +execution counts to be tallied and displayed. + +@item -i +@itemx --file-info +The @samp{-i} option causes @code{gprof} to display summary information +about the profile data file(s) and then exit. The number of histogram, +call graph, and basic-block count records is displayed. + +@item -I @var{dirs} +@itemx --directory-path=@var{dirs} +The @samp{-I} option specifies a list of search directories in +which to find source files. Environment variable @var{GPROF_PATH} +can also be used to convery this information. +Used mostly for annotated source output. + +@item -J[@var{symspec}] +@itemx --no-annotated-source[=@var{symspec}] +The @samp{-J} option causes @code{gprof} not to +print annotated source code. +If @var{symspec} is specified, @code{gprof} prints annotated source, +but excludes matching symbols. + +@item -L +@itemx --print-path +Normally, source filenames are printed with the path +component suppressed. The @samp{-L} option causes @code{gprof} +to print the full pathname of +source filenames, which is determined +from symbolic debugging information in the image file +and is relative to the directory in which the compiler +was invoked. + +@item -p[@var{symspec}] +@itemx --flat-profile[=@var{symspec}] +The @samp{-p} option causes @code{gprof} to print a flat profile. +If @var{symspec} is specified, print flat profile only for matching symbols. +@xref{Flat Profile}. + +@item -P[@var{symspec}] +@itemx --no-flat-profile[=@var{symspec}] +The @samp{-P} option causes @code{gprof} to suppress printing a flat profile. +If @var{symspec} is specified, @code{gprof} prints a flat profile, +but excludes matching symbols. + +@item -q[@var{symspec}] +@itemx --graph[=@var{symspec}] +The @samp{-q} option causes @code{gprof} to print the call graph analysis. +If @var{symspec} is specified, print call graph only for matching symbols +and their children. +@xref{Call Graph}. + +@item -Q[@var{symspec}] +@itemx --no-graph[=@var{symspec}] +The @samp{-Q} option causes @code{gprof} to suppress printing the +call graph. +If @var{symspec} is specified, @code{gprof} prints a call graph, +but excludes matching symbols. + +@item -y +@itemx --separate-files +This option affects annotated source output only. +Normally, gprof prints annotated source files +to standard-output. If this option is specified, +annotated source for a file named @file{path/filename} +is generated in the file @file{filename-ann}. + +@item -Z[@var{symspec}] +@itemx --no-exec-counts[=@var{symspec}] +The @samp{-Z} option causes @code{gprof} not to +print a tally of functions and the number of times each was called. +If @var{symspec} is specified, print tally, but exclude matching symbols. + +@item --function-ordering +The @samp{--function-ordering} option causes @code{gprof} to print a +suggested function ordering for the program based on profiling data. +This option suggests an ordering which may improve paging, tlb and +cache behavior for the program on systems which support arbitrary +ordering of functions in an executable. + +The exact details of how to force the linker to place functions +in a particular order is system dependent and out of the scope of this +manual. + +@item --file-ordering @var{map_file} +The @samp{--file-ordering} option causes @code{gprof} to print a +suggested .o link line ordering for the program based on profiling data. +This option suggests an ordering which may improve paging, tlb and +cache behavior for the program on systems which do not support arbitrary +ordering of functions in an executable. + +Use of the @samp{-a} argument is highly recommended with this option. + +The @var{map_file} argument is a pathname to a file which provides +function name to object file mappings. The format of the file is similar to +the output of the program @code{nm}. + +@smallexample +@group +c-parse.o:00000000 T yyparse +c-parse.o:00000004 C yyerrflag +c-lang.o:00000000 T maybe_objc_method_name +c-lang.o:00000000 T print_lang_statistics +c-lang.o:00000000 T recognize_objc_keyword +c-decl.o:00000000 T print_lang_identifier +c-decl.o:00000000 T print_lang_type +@dots{} + +@end group +@end smallexample + +GNU @code{nm} @samp{--extern-only} @samp{--defined-only} @samp{-v} @samp{--print-file-name} can be used to create @var{map_file}. + +@item -T +@itemx --traditional +The @samp{-T} option causes @code{gprof} to print its output in +``traditional'' BSD style. + +@item -w @var{width} +@itemx --width=@var{width} +Sets width of output lines to @var{width}. +Currently only used when printing the function index at the bottom +of the call graph. + +@item -x +@itemx --all-lines +This option affects annotated source output only. +By default, only the lines at the beginning of a basic-block +are annotated. If this option is specified, every line in +a basic-block is annotated by repeating the annotation for the +first line. This behavior is similar to @code{tcov}'s @samp{-a}. + +@end table + +@node Analysis Options,Miscellaneous Options,Output Options,Invoking +@section Analysis Options + +@table @code + @item -a +@itemx --no-static The @samp{-a} option causes @code{gprof} to suppress the printing of statically declared (private) functions. (These are functions whose names are not listed as global, and which are not visible outside the @@ -294,12 +495,113 @@ function that was loaded directly before it in the executable file. @c This is compatible with Unix @code{gprof}, but a bad idea. This option affects both the flat profile and the call graph. +@item -c +@itemx --static-call-graph +The @samp{-c} option causes the call graph of the program to be +augmented by a heuristic which examines the text space of the object +file and identifies function calls in the binary machine code. +Since normal call graph records are only generated when functions are +entered, this option identifies children that could have been called, +but never were. Calls to functions that were not compiled with +profiling enabled are also identified, but only if symbol table +entries are present for them. +Calls to dynamic library routines are typically @emph{not} found +by this option. +Parents or children identified via this heuristic +are indicated in the call graph with call counts of @samp{0}. + @item -D +@itemx --ignore-non-functions The @samp{-D} option causes @code{gprof} to ignore symbols which are not known to be functions. This option will give more accurate profile data on systems where it is supported (Solaris and HPUX for example). +@item -k @var{from}/@var{to} +The @samp{-k} option allows you to delete from the call graph any arcs from +symbols matching symspec @var{from} to those matching symspec @var{to}. + +@item -l +@itemx --line +The @samp{-l} option enables line-by-line profiling, which causes +histogram hits to be charged to individual source code lines, +instead of functions. +If the program was compiled with basic-block counting enabled, +this option will also identify how many times each line of +code was executed. +While line-by-line profiling can help isolate where in a large function +a program is spending its time, it also significantly increases +the running time of @code{gprof}, and magnifies statistical +inaccuracies. +@xref{Sampling Error}. + +@item -m @var{num} +@itemx --min-count=@var{num} +This option affects execution count output only. +Symbols that are executed less than @var{num} times are suppressed. + +@item -n[@var{symspec}] +@itemx --time[=@var{symspec}] +The @samp{-n} option causes @code{gprof}, in its call graph analysis, +to only propagate times for symbols matching @var{symspec}. + +@item -N[@var{symspec}] +@itemx --no-time[=@var{symspec}] +The @samp{-n} option causes @code{gprof}, in its call graph analysis, +not to propagate times for symbols matching @var{symspec}. + +@item -z +@itemx --display-unused-functions +If you give the @samp{-z} option, @code{gprof} will mention all +functions in the flat profile, even those that were never called, and +that had no time spent in them. This is useful in conjunction with the +@samp{-c} option for discovering which routines were never called. + +@end table + +@node Miscellaneous Options,Depricated Options,Analysis Options,Invoking +@section Miscellaneous Options + +@table @code + +@item -d[@var{num}] +@itemx --debug[=@var{num}] +The @samp{-d @var{num}} option specifies debugging options. +If @var{num} is not specified, enable all debugging. +@xref{Debugging}. + +@item -O@var{name} +@itemx --file-format=@var{name} +Selects the format of the profile data files. +Recognized formats are @samp{auto} (the default), @samp{bsd}, @samp{magic}, +and @samp{prof} (not yet supported). + +@item -s +@itemx --sum +The @samp{-s} option causes @code{gprof} to summarize the information +in the profile data files it read in, and write out a profile data +file called @file{gmon.sum}, which contains all the information from +the profile data files that @code{gprof} read in. The file @file{gmon.sum} +may be one of the specified input files; the effect of this is to +merge the data in the other input files into @file{gmon.sum}. + +Eventually you can run @code{gprof} again without @samp{-s} to analyze the +cumulative data in the file @file{gmon.sum}. + +@item -v +@itemx --version +The @samp{-v} flag causes @code{gprof} to print the current version +number, and then exit. + +@end table + +@node Depricated Options,Symspecs,Miscellaneous Options,Invoking +@section Depricated Options + +@table @code + +These options have been replaced with newer versions that use symspecs. + @item -e @var{function_name} The @samp{-e @var{function}} option tells @code{gprof} to not print information about the function @var{function_name} (and its @@ -331,23 +633,8 @@ percentages-of-time for the call graph. More than one @samp{-F} option may be given; only one @var{function_name} may be indicated with each @samp{-F} option. The @samp{-F} option overrides the @samp{-E} option. -@item -k @var{from@dots{}} @var{to@dots{}} -The @samp{-k} option allows you to delete from the profile any arcs from -routine @var{from} to routine @var{to}. - -@item -v -The @samp{-v} flag causes @code{gprof} to print the current version -number, and then exit. - -@item -z -If you give the @samp{-z} option, @code{gprof} will mention all -functions in the flat profile, even those that were never called, and -that had no time spent in them. This is useful in conjunction with the -@samp{-c} option for discovering which routines were never called. @end table -The order of these options does not matter. - Note that only one function can be specified with each @code{-e}, @code{-E}, @code{-f} or @code{-F} option. To specify more than one function, use multiple options. For example, this command: @@ -360,84 +647,76 @@ gprof -e boring -f foo -f bar myprogram > gprof.output lists in the call graph all functions that were reached from either @code{foo} or @code{bar} and were not reachable from @code{boring}. -There are a few other useful @code{gprof} options: - -@table @code -@item -b -If the @samp{-b} option is given, @code{gprof} doesn't print the -verbose blurbs that try to explain the meaning of all of the fields in -the tables. This is useful if you intend to print out the output, or -are tired of seeing the blurbs. - -@item -c -The @samp{-c} option causes the static call-graph of the program to be -discovered by a heuristic which examines the text space of the object -file. Static-only parents or children are indicated with call counts of -@samp{0}. - -@item -d @var{num} -The @samp{-d @var{num}} option specifies debugging options. -@c @xref{debugging}. - -@item -s -The @samp{-s} option causes @code{gprof} to summarize the information -in the profile data files it read in, and write out a profile data -file called @file{gmon.sum}, which contains all the information from -the profile data files that @code{gprof} read in. The file @file{gmon.sum} -may be one of the specified input files; the effect of this is to -merge the data in the other input files into @file{gmon.sum}. -@xref{Sampling Error}. - -Eventually you can run @code{gprof} again without @samp{-s} to analyze the -cumulative data in the file @file{gmon.sum}. +@node Symspecs,,Depricated Options,Invoking +@section Symspecs -@item -T -The @samp{-T} option causes @code{gprof} to print its output in -``traditional'' BSD style. - -@item --function-ordering -The @samp{--function-ordering} option causes @code{gprof} to print a -suggested function ordering for the program based on profiling data. -This option suggests an ordering which may improve paging, tlb and -cache behavior for the program on systems which support arbitrary -ordering of functions in an executable. +Many of the output options allow functions to be included or excluded +using @dfn{symspecs} (symbol specifications), which observe the +following syntax: -The exact details of how to force the linker to place functions -in a particular order is system dependent and out of the scope of this -manual. +@example + filename_containing_a_dot +| funcname_not_containing_a_dot +| linenumber +| ( [ any_filename ] `:' ( any_funcname | linenumber ) ) +@end example -@item --file-ordering @var{map_file} -The @samp{--file-ordering} option causes @code{gprof} to print a -suggested .o link line ordering for the program based on profiling data. -This option suggests an ordering which may improve paging, tlb and -cache behavior for the program on systems which do not support arbitrary -ordering of functions in an executable. +Here are some sample symspecs: -Use of the @samp{-a} argument is highly recommended with this option. +@table @code +@item main.c +Selects everything in file "main.c"---the +dot in the string tells gprof to interpret +the string as a filename, rather than as +a function name. To select a file whose +name does not contain a dot, a trailing colon +should be specified. For example, "odd:" is +interpreted as the file named "odd". + +@item main +Selects all functions named "main". Notice +that there may be multiple instances of the +same function name because some of the +definitions may be local (i.e., static). +Unless a function name is unique in a program, +you must use the colon notation explained +below to specify a function from a specific +source file. Sometimes, function names contain +dots. In such cases, it is necessar to +add a leading colon to the name. For example, +":.mul" selects function ".mul". + +@item main.c:main +Selects function "main" in file "main.c". + +@item main.c:134 +Selects line 134 in file "main.c". +@end table -The @var{map_file} argument is a pathname to a file which provides -function name to object file mappings. The format of the file is similar to -the output of the program @code{nm}. +@node Output +@chapter Interpreting @code{gprof}'s Output -@smallexample -@group -c-parse.o:00000000 T yyparse -c-parse.o:00000004 C yyerrflag -c-lang.o:00000000 T maybe_objc_method_name -c-lang.o:00000000 T print_lang_statistics -c-lang.o:00000000 T recognize_objc_keyword -c-decl.o:00000000 T print_lang_identifier -c-decl.o:00000000 T print_lang_type -@dots{} +@code{gprof} can produce several different output styles, the +most important of which are described below. The simplest output +styles (file information, execution count, and function and file ordering) +are not described here, but are documented with the respective options +that trigger them. +@xref{Output Options}. -@end group -@end smallexample +@menu +* Flat Profile:: The flat profile shows how much time was spent + executing directly in each function. +* Call Graph:: The call graph shows which functions called which + others, and how much time each function used + when its subroutine calls are included. +* Line-by-line:: @code{gprof} can analyze individual source code lines +* Annotated Source:: The annotated source listing displays source code + labeled with execution counts +@end menu -GNU @code{nm} @samp{--extern-only} @samp{--defined-only} @samp{-v} @samp{--print-file-name} can be used to create @var{map_file}. -@end table -@node Flat Profile -@chapter How to Understand the Flat Profile +@node Flat Profile,Call Graph,,Output +@section The Flat Profile @cindex flat profile The @dfn{flat profile} shows the total amount of time your program @@ -476,17 +755,42 @@ Each sample counts as 0.01 seconds. @end smallexample @noindent -The functions are sorted by decreasing run-time spent in them. The +The functions are sorted by first by decreasing run-time spent in them, +then by decreasing number of calls, then alphabetically by name. The functions @samp{mcount} and @samp{profil} are part of the profiling aparatus and appear in every flat profile; their time gives a measure of the amount of overhead due to profiling. -The sampling period estimates the margin of error in each of the time +Just before the column headers, a statement appears indicating +how much time each sample counted as. +This @dfn{sampling period} estimates the margin of error in each of the time figures. A time figure that is not much larger than this is not -reliable. In this example, the @samp{self seconds} field for -@samp{mcount} might well be @samp{0} or @samp{0.04} in another run. +reliable. In this example, each sample counted as 0.01 seconds, +suggesting a 100 Hz sampling rate. +The program's total execution time was 0.06 +seconds, as indicated by the @samp{cumulative seconds} field. Since +each sample counted for 0.01 seconds, this means only six samples +were taken during the run. Two of the samples occured while the +program was in the @samp{open} function, as indicated by the +@samp{self seconds} field. Each of the other four samples +occured one each in @samp{offtime}, @samp{memccpy}, @samp{write}, +and @samp{mcount}. +Since only six samples were taken, none of these values can +be regarded as particularly reliable. +In another run, +the @samp{self seconds} field for +@samp{mcount} might well be @samp{0.00} or @samp{0.02}. @xref{Sampling Error}, for a complete discussion. +The remaining functions in the listing (those whose +@samp{self seconds} field is @samp{0.00}) didn't appear +in the histogram samples at all. However, the call graph +indicated that they were called, so therefore they are listed, +sorted in decreasing order by the @samp{calls} field. +Clearly some time was spent executing these functions, +but the paucity of histogram samples prevents any +determination of how much time each took. + Here is what the fields in each line mean: @table @code @@ -518,14 +822,16 @@ is blank for this function. This represents the average number of milliseconds spent in this function and its descendants per call, if this function is profiled. Otherwise, this field is blank for this function. +This is the only field in the flat profile that uses call graph analysis. @item name This is the name of the function. The flat profile is sorted by this -field alphabetically after the @dfn{self seconds} field is sorted. +field alphabetically after the @dfn{self seconds} and @dfn{calls} +fields are sorted. @end table -@node Call Graph -@chapter How to Read the Call Graph +@node Call Graph,Line-by-line,Flat Profile,Output +@section The Call Graph @cindex call graph The @dfn{call graph} shows how much time was spent in each function @@ -593,7 +899,7 @@ is never mentioned in the call graph. @end menu @node Primary -@section The Primary Line +@subsection The Primary Line The @dfn{primary line} in a call graph entry is the line that describes the function which the entry is about and gives the overall @@ -668,7 +974,7 @@ gnurr <cycle 1> [12] @end table @node Callers, Subroutines, Primary, Call Graph -@section Lines for a Function's Callers +@subsection Lines for a Function's Callers A function's entry has a line for each function it was called by. These lines' fields correspond to the fields of the primary line, but @@ -726,7 +1032,7 @@ signal handlers. @c FIXME - still relevant? @node Subroutines, Cycles, Callers, Call Graph -@section Lines for a Function's Subroutines +@subsection Lines for a Function's Subroutines A function's entry has a line for each of its subroutines---in other words, a line for each other function that it called. These lines' @@ -762,6 +1068,9 @@ of the total time spent in calls to @code{report} from @code{main}. @item called Two numbers, the number of calls to @code{report} from @code{main} followed by the total number of nonrecursive calls to @code{report}. +This ratio is used to determine how much of @code{report}'s @code{self} +and @code{children} time gets credited to @code{main}. +@xref{Assumptions}. @item name The name of the subroutine of @code{main} to which this line applies, @@ -772,7 +1081,7 @@ printed between the name and the index number. @end table @node Cycles,, Subroutines, Call Graph -@section How Mutually Recursive Functions Are Described +@subsection How Mutually Recursive Functions Are Described @cindex cycle @cindex recursion cycle @@ -782,7 +1091,7 @@ another function that (directly or indirectly) calls (or appears to call) the original function. For example: if @code{a} calls @code{b}, and @code{b} calls @code{a}, then @code{a} and @code{b} form a cycle. -Whenever there are call-paths both ways between a pair of functions, they +Whenever there are call paths both ways between a pair of functions, they belong to the same cycle. If @code{a} and @code{b} call each other and @code{b} and @code{c} call each other, all three make one cycle. Note that even if @code{b} only calls @code{a} if it was not called from @code{a}, @@ -906,44 +1215,188 @@ function in the cycle. The @code{self} and @code{children} fields in these lines are blank because of the difficulty of defining meanings for them when recursion is going on. -@node Implementation, Sampling Error, Call Graph, Top -@chapter Implementation of Profiling +@node Line-by-line,Annotated Source,Call Graph,Output +@section Line-by-line Profiling -Profiling works by changing how every function in your program is compiled -so that when it is called, it will stash away some information about where -it was called from. From this, the profiler can figure out what function -called it, and can count how many times it was called. This change is made -by the compiler when your program is compiled with the @samp{-pg} option. +@code{gprof}'s @samp{-l} option causes the program to perform +@dfn{line-by-line} profiling. In this mode, histogram +samples are assigned not to functions, but to individual +lines of source code. The program usually must be compiled +with a @samp{-g} option, in addition to @samp{-pg}, in order +to generate debugging symbols for tracking source code lines. -Profiling also involves watching your program as it runs, and keeping a -histogram of where the program counter happens to be every now and then. -Typically the program counter is looked at around 100 times per second of -run time, but the exact frequency may vary from system to system. +The flat profile is the most useful output table +in line-by-line mode. +The call graph isn't as useful as normal, since +the current version of @code{gprof} does not propagate +call graph arcs from source code lines to the enclosing function. +The call graph does, however, show each line of code +that called each function, along with a count. -A special startup routine allocates memory for the histogram and sets up -a clock signal handler to make entries in it. Use of this special -startup routine is one of the effects of using @samp{gcc @dots{} -pg} to -link. The startup file also includes an @samp{exit} function which is -responsible for writing the file @file{gmon.out}. +Here is a section of @code{gprof}'s output, without line-by-line profiling. +Note that @code{ct_init} accounted for four histogram hits, and +13327 calls to @code{init_block}. -Number-of-calls information for library routines is collected by using a -special version of the C library. The programs in it are the same as in -the usual C library, but they were compiled with @samp{-pg}. If you -link your program with @samp{gcc @dots{} -pg}, it automatically uses the -profiling version of the library. +@smallexample +Flat profile: -The output from @code{gprof} gives no indication of parts of your program that -are limited by I/O or swapping bandwidth. This is because samples of the -program counter are taken at fixed intervals of run time. Therefore, the -time measurements in @code{gprof} output say nothing about time that your -program was not running. For example, a part of the program that creates -so much data that it cannot all fit in physical memory at once may run very -slowly due to thrashing, but @code{gprof} will say it uses little time. On -the other hand, sampling by run time has the advantage that the amount of -load due to other users won't directly affect the output you get. +Each sample counts as 0.01 seconds. + % cumulative self self total + time seconds seconds calls us/call us/call name + 30.77 0.13 0.04 6335 6.31 6.31 ct_init -@node Sampling Error, Assumptions, Implementation, Top -@chapter Statistical Inaccuracy of @code{gprof} Output + + Call graph (explanation follows) + + +granularity: each sample hit covers 4 byte(s) for 7.69% of 0.13 seconds + +index % time self children called name + + 0.00 0.00 1/13496 name_too_long + 0.00 0.00 40/13496 deflate + 0.00 0.00 128/13496 deflate_fast + 0.00 0.00 13327/13496 ct_init +[7] 0.0 0.00 0.00 13496 init_block + +@end smallexample + +Now let's look at some of @code{gprof}'s output from the same program run, +this time with line-by-line profiling enabled. Note that @code{ct_init}'s +four histogram hits are broken down into four lines of source code - one hit +occured on each of lines 349, 351, 382 and 385. In the call graph, +note how +@code{ct_init}'s 13327 calls to @code{init_block} are broken down +into one call from line 396, 3071 calls from line 384, 3730 calls +from line 385, and 6525 calls from 387. + +@smallexample +Flat profile: + +Each sample counts as 0.01 seconds. + % cumulative self + time seconds seconds calls name + 7.69 0.10 0.01 ct_init (trees.c:349) + 7.69 0.11 0.01 ct_init (trees.c:351) + 7.69 0.12 0.01 ct_init (trees.c:382) + 7.69 0.13 0.01 ct_init (trees.c:385) + + + Call graph (explanation follows) + + +granularity: each sample hit covers 4 byte(s) for 7.69% of 0.13 seconds + + % time self children called name + + 0.00 0.00 1/13496 name_too_long (gzip.c:1440) + 0.00 0.00 1/13496 deflate (deflate.c:763) + 0.00 0.00 1/13496 ct_init (trees.c:396) + 0.00 0.00 2/13496 deflate (deflate.c:727) + 0.00 0.00 4/13496 deflate (deflate.c:686) + 0.00 0.00 5/13496 deflate (deflate.c:675) + 0.00 0.00 12/13496 deflate (deflate.c:679) + 0.00 0.00 16/13496 deflate (deflate.c:730) + 0.00 0.00 128/13496 deflate_fast (deflate.c:654) + 0.00 0.00 3071/13496 ct_init (trees.c:384) + 0.00 0.00 3730/13496 ct_init (trees.c:385) + 0.00 0.00 6525/13496 ct_init (trees.c:387) +[6] 0.0 0.00 0.00 13496 init_block (trees.c:408) + +@end smallexample + + +@node Annotated Source,,Line-by-line,Output +@section The Annotated Source Listing + +@code{gprof}'s @samp{-A} option triggers an annotated source listing, +which lists the program's source code, each function labeled with the +number of times it was called. You may also need to specify the +@samp{-I} option, if @code{gprof} can't find the source code files. + +Compiling with @samp{gcc @dots{} -g -pg -a} augments your program +with basic-block counting code, in addition to function counting code. +This enables @code{gprof} to determine how many times each line +of code was exeucted. +For example, consider the following function, taken from gzip, +with line numbers added: + +@smallexample + 1 ulg updcrc(s, n) + 2 uch *s; + 3 unsigned n; + 4 @{ + 5 register ulg c; + 6 + 7 static ulg crc = (ulg)0xffffffffL; + 8 + 9 if (s == NULL) @{ +10 c = 0xffffffffL; +11 @} else @{ +12 c = crc; +13 if (n) do @{ +14 c = crc_32_tab[...]; +15 @} while (--n); +16 @} +17 crc = c; +18 return c ^ 0xffffffffL; +19 @} + +@end smallexample + +@code{updcrc} has at least five basic-blocks. +One is the function itself. The +@code{if} statement on line 9 generates two more basic-blocks, one +for each branch of the @code{if}. A fourth basic-block results from +the @code{if} on line 13, and the contents of the @code{do} loop form +the fifth basic-block. The compiler may also generate additional +basic-blocks to handle various special cases. + +A program augmented for basic-block counting can be analyzed with +@code{gprof -l -A}. I also suggest use of the @samp{-x} option, +which ensures that each line of code is labeled at least once. +Here is @code{updcrc}'s +annotated source listing for a sample @code{gzip} run: + +@smallexample + ulg updcrc(s, n) + uch *s; + unsigned n; + 2 ->@{ + register ulg c; + + static ulg crc = (ulg)0xffffffffL; + + 2 -> if (s == NULL) @{ + 1 -> c = 0xffffffffL; + 1 -> @} else @{ + 1 -> c = crc; + 1 -> if (n) do @{ + 26312 -> c = crc_32_tab[...]; +26312,1,26311 -> @} while (--n); + @} + 2 -> crc = c; + 2 -> return c ^ 0xffffffffL; + 2 ->@} +@end smallexample + +In this example, the function was called twice, passing once through +each branch of the @code{if} statement. The body of the @code{do} +loop was executed a total of 26312 times. Note how the @code{while} +statement is annotated. It began execution 26312 times, once for +each iteration through the loop. One of those times (the last time) +it exited, while it branched back to the beginning of the loop 26311 times. + +@node Inaccuracy +@chapter Inaccuracy of @code{gprof} Output + +@menu +* Sampling Error:: Statistical margins of error +* Assumptions:: Estimating children times +@end menu + +@node Sampling Error,Assumptions,,Inaccuracy +@section Statistical Sampling Error The run-time figures that @code{gprof} gives you are based on a sampling process, so they are subject to statistical inaccuracy. If a function runs @@ -951,7 +1404,8 @@ only a small amount of time, so that on the average the sampling process ought to catch that function in the act only once, there is a pretty good chance it will actually find that function zero times, or twice. -By contrast, the number-of-calls figures are derived by counting, not +By contrast, the number-of-calls and basic-block figures +are derived by counting, not sampling. They are completely accurate and will not vary from run to run if your program is deterministic. @@ -960,11 +1414,18 @@ profile says how often samples are taken. The rule of thumb is that a run-time figure is accurate if it is considerably bigger than the sampling period. -The actual amount of error is usually more than one sampling period. In -fact, if a value is @var{n} times the sampling period, the @emph{expected} -error in it is the square-root of @var{n} sampling periods. If the -sampling period is 0.01 seconds and @code{foo}'s run-time is 1 second, the -expected error in @code{foo}'s run-time is 0.1 seconds. It is likely to +The actual amount of error can be predicted. +For @var{n} samples, the @emph{expected} error +is the square-root of @var{n}. For example, +if the sampling period is 0.01 seconds and @code{foo}'s run-time is 1 second, +@var{n} is 100 samples (1 second/0.01 seconds), sqrt(@var{n}) is 10 samples, so +the expected error in @code{foo}'s run-time is 0.1 seconds (10*0.01 seconds), +or ten percent of the observed value. +Again, if the sampling period is 0.01 seconds and @code{bar}'s run-time is +100 seconds, @var{n} is 10000 samples, sqrt(@var{n}) is 100 samples, so +the expected error in @code{bar}'s run-time is 1 second, +or one percent of the observed value. +It is likely to vary this much @emph{on the average} from one profiling run to the next. (@emph{Sometimes} it will vary more.) @@ -1005,8 +1466,8 @@ gprof @var{executable-file} gmon.sum > @var{output-file} @end example @end enumerate -@node Assumptions, Incompatibilities, Sampling Error, Top -@chapter Estimating @code{children} Times Uses an Assumption +@node Assumptions,,Sampling Error,Inaccuracy +@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 @@ -1036,7 +1497,49 @@ We hope some day to put more complete data into @file{gmon.out}, so that this assumption is no longer needed, if we can figure out how. For the nonce, the estimated figures are usually more useful than misleading. -@node Incompatibilities, , Assumptions, Top +@node How do I? +@chapter Answers to Common Questions + +@table @asis +@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 +use the following pipeline: + +@example +gprof -l -C @var{objfile} | sort -k 3 -n -r +@end example + +This listing will show you the lines in your code executed most often, +but not necessarily those that consumed the most time. + +@item How do I find which lines in my program called a particular function? + +Use @code{gprof -l} and lookup the function in the call graph. +The callers will be broken down by function and line number. + +@item How do I analyze a program that runs for less than a second? + +Try using a shell script like this one: + +@example +for i in `seq 1 100`; do + fastprog + mv gmon.out gmon.out.$i +done + +gprof -s fastprog gmon.out.* + +gprof fastprog gmon.sum +@end example + +If your program is completely deterministic, all the call counts +will be simple multiples of 100 (i.e. a function called once in +each run will appear with a call count of 100). + +@end table + +@node Incompatibilities @chapter Incompatibilities with Unix @code{gprof} @sc{gnu} @code{gprof} and Berkeley Unix @code{gprof} use the same data @@ -1045,6 +1548,13 @@ there are a few differences. @itemize @bullet @item +@sc{gnu} @code{gprof} uses a new, generalized file format with support +for basic-block execution counts and non-realtime histograms. A magic +cookie and version number allows @code{gprof} to easily identify +new style files. Old BSD-style files can still be read. +@xref{File Format}. + +@item For a recursive function, Unix @code{gprof} lists the function as a parent and as a child, with a @code{calls} field that lists the number of recursive calls. @sc{gnu} @code{gprof} omits these lines and puts @@ -1054,6 +1564,15 @@ the number of recursive calls in the primary line. When a function is suppressed from the call graph with @samp{-e}, @sc{gnu} @code{gprof} still lists it as a subroutine of functions that call it. +@item +@sc{gnu} @code{gprof} accepts the @samp{-k} with its argument +in the form @samp{from/to}, instead of @samp{from to}. + +@item +In the annotated source listing, +if there are multiple basic blocks on the same line, +@sc{gnu} @code{gprof} prints all of their counts, seperated by commas. + @ignore - it does this now @item The function names printed in @sc{gnu} @code{gprof} output do not include @@ -1067,35 +1586,431 @@ The blurbs, field widths, and output formats are different. @sc{gnu} tables without skipping the blurbs. @end itemize -@contents -@bye +@node Details +@chapter Details of Profiling -NEEDS AN INDEX +@menu +* Implementation:: How a program collets profiling information +* File Format:: Format of @samp{gmon.out} files +* Internals:: @code{gprof}'s internal operation +* Debugging:: Using @code{gprof}'s @samp{-d} option +@end menu + +@node Implementation,File Format,,Details +@section Implementation of Profiling + +Profiling works by changing how every function in your program is compiled +so that when it is called, it will stash away some information about where +it was called from. From this, the profiler can figure out what function +called it, and can count how many times it was called. This change is made +by the compiler when your program is compiled with the @samp{-pg} option, +which causes every function to call @code{mcount} +(or @code{_mcount}, or @code{__mcount}, depending on the OS and compiler) +as one of its first operations. + +The @code{mcount} routine, included in the profiling library, +is responsible for recording in an in-memory call graph table +both its parent routine (the child) and its parent's parent. This is +typically done by examining the stack frame to find both +the address of the child, and the return address in the original parent. +Since this is a very machine-dependant operation, @code{mcount} +itself is typically a short assembly-language stub routine +that extracts the required +information, and then calls @code{__mcount_internal} +(a normal C function) with two arguments - @code{frompc} and @code{selfpc}. +@code{__mcount_internal} is responsible for maintaining +the in-memory call graph, which records @code{frompc}, @code{selfpc}, +and the number of times each of these call arcs was transversed. + +GCC Version 2 provides a magical function (@code{__builtin_return_address}), +which allows a generic @code{mcount} function to extract the +required information from the stack frame. However, on some +architectures, most notably the SPARC, using this builtin can be +very computationally expensive, and an assembly language version +of @code{mcount} is used for performance reasons. + +Number-of-calls information for library routines is collected by using a +special version of the C library. The programs in it are the same as in +the usual C library, but they were compiled with @samp{-pg}. If you +link your program with @samp{gcc @dots{} -pg}, it automatically uses the +profiling version of the library. + +Profiling also involves watching your program as it runs, and keeping a +histogram of where the program counter happens to be every now and then. +Typically the program counter is looked at around 100 times per second of +run time, but the exact frequency may vary from system to system. -Still relevant? - The @file{gmon.out} file is written in the program's @emph{current working - directory} at the time it exits. This means that if your program calls - @code{chdir}, the @file{gmon.out} file will be left in the last directory - your program @code{chdir}'d to. If you don't have permission to write in - this directory, the file is not written. You may get a confusing error - message if this happens. (We have not yet replaced the part of Unix - responsible for this; when we do, we will make the error message - comprehensible.) +This is done is one of two ways. Most UNIX-like operating systems +provide a @code{profil()} system call, which registers a memory +array with the kernel, along with a scale +factor that determines how the program's address space maps +into the array. +Typical scaling values cause every 2 to 8 bytes of address space +to map into a single array slot. +On every tick of the system clock +(assuming the profiled program is running), the value of the +program counter is examined and the corresponding slot in +the memory array is incremented. Since this is done in the kernel, +which had to interrupt the process anyway to handle the clock +interrupt, very little additional system overhead is required. + +However, some operating systems, most notably Linux 2.0 (and earlier), +do not provide a @code{profil()} system call. On such a system, +arrangements are made for the kernel to periodically deliver +a signal to the process (typically via @code{setitimer()}), +which then performs the same operation of examining the +program counter and incrementing a slot in the memory array. +Since this method requires a signal to be delivered to +user space every time a sample is taken, it uses considerably +more overhead than kernel-based profiling. Also, due to the +added delay required to deliver the signal, this method is +less accurate as well. + +A special startup routine allocates memory for the histogram and +either calls @code{profil()} or sets up +a clock signal handler. +This routine (@code{monstartup}) can be invoked in several ways. +On Linux systems, a special profiling startup file @code{gcrt0.o}, +which invokes @code{monstartup} before @code{main}, +is used instead of the default @code{crt0.o}. +Use of this special startup file is one of the effects +of using @samp{gcc @dots{} -pg} to link. +On SPARC systems, no special startup files are used. +Rather, the @code{mcount} routine, when it is invoked for +the first time (typically when @code{main} is called), +calls @code{monstartup}. + +If the compiler's @samp{-a} option was used, basic-block counting +is also enabled. Each object file is then compiled with a static array +of counts, initially zero. +In the executable code, every time a new basic-block begins +(i.e. when an @code{if} statement appears), an extra instruction +is inserted to increment the corresponding count in the array. +At compile time, a paired array was constructed that recorded +the starting address of each basic-block. Taken together, +the two arrays record the starting address of every basic-block, +along with the number of times it was executed. + +The profiling library also includes a function (@code{mcleanup}) which is +typically registered using @code{atexit()} to be called as the +program exits, and is responsible for writing the file @file{gmon.out}. +Profiling is turned off, various headers are output, and the histogram +is written, followed by the call-graph arcs and the basic-block counts. --k from to...? +The output from @code{gprof} gives no indication of parts of your program that +are limited by I/O or swapping bandwidth. This is because samples of the +program counter are taken at fixed intervals of the program's run time. +Therefore, the +time measurements in @code{gprof} output say nothing about time that your +program was not running. For example, a part of the program that creates +so much data that it cannot all fit in physical memory at once may run very +slowly due to thrashing, but @code{gprof} will say it uses little time. On +the other hand, sampling by run time has the advantage that the amount of +load due to other users won't directly affect the output you get. + +@node File Format,Internals,Implementation,Details +@section Profiling Data File Format + +The old BSD-derived file format used for profile data does not contain a +magic cookie that allows to check whether a data file really is a +gprof file. Furthermore, it does not provide a version number, thus +rendering changes to the file format almost impossible. @sc{gnu} @code{gprof} +uses a new file format that provides these features. For backward +compatibility, @sc{gnu} @code{gprof} continues to support the old BSD-derived +format, but not all features are supported with it. For example, +basic-block execution counts cannot be accommodated by the old file +format. + +The new file format is defined in header file @file{gmon_out.h}. It +consists of a header containing the magic cookie and a version number, +as well as some spare bytes available for future extensions. All data +in a profile data file is in the native format of the host on which +the profile was collected. @sc{gnu} @code{gprof} adapts automatically to the +byte-order in use. + +In the new file format, the header is followed by a sequence of +records. Currently, there are three different record types: histogram +records, call-graph arc records, and basic-block execution count +records. Each file can contain any number of each record type. When +reading a file, @sc{gnu} @code{gprof} will ensure records of the same type are +compatible with each other and compute the union of all records. For +example, for basic-block execution counts, the union is simply the sum +of all execution counts for each basic-block. + +@subsection Histogram Records + +Histogram records consist of a header that is followed by an array of +bins. The header contains the text-segment range that the histogram +spans, the size of the histogram in bytes (unlike in the old BSD +format, this does not include the size of the header), the rate of the +profiling clock, and the physical dimension that the bin counts +represent after being scaled by the profiling clock rate. The +physical dimension is specified in two parts: a long name of up to 15 +characters and a single character abbreviation. For example, a +histogram representing real-time would specify the long name as +"seconds" and the abbreviation as "s". This feature is useful for +architectures that support performance monitor hardware (which, +fortunately, is becoming increasingly common). For example, under DEC +OSF/1, the "uprofile" command can be used to produce a histogram of, +say, instruction cache misses. In this case, the dimension in the +histogram header could be set to "i-cache misses" and the abbreviation +could be set to "1" (because it is simply a count, not a physical +dimension). Also, the profiling rate would have to be set to 1 in +this case. + +Histogram bins are 16-bit numbers and each bin represent an equal +amount of text-space. For example, if the text-segment is one +thousand bytes long and if there are ten bins in the histogram, each +bin represents one hundred bytes. + + +@subsection Call-Graph Records + +Call-graph records have a format that is identical to the one used in +the BSD-derived file format. It consists of an arc in the call graph +and a count indicating the number of times the arc was traversed +during program execution. Arcs are specified by a pair of addresses: +the first must be within caller's function and the second must be +within the callee's function. When performing profiling at the +function level, these addresses can point anywhere within the +respective function. However, when profiling at the line-level, it is +better if the addresses are as close to the call-site/entry-point as +possible. This will ensure that the line-level call-graph is able to +identify exactly which line of source code performed calls to a +function. + +@subsection Basic-Block Execution Count Records + +Basic-block execution count records consist of a header followed by a +sequence of address/count pairs. The header simply specifies the +length of the sequence. In an address/count pair, the address +identifies a basic-block and the count specifies the number of times +that basic-block was executed. Any address within the basic-address can +be used. + +@node Internals,Debugging,File Format,Details +@section @code{gprof}'s Internal Operation + +Like most programs, @code{gprof} begins by processing its options. +During this stage, it may building its symspec list +(@code{sym_ids.c:sym_id_add}), if +options are specified which use symspecs. +@code{gprof} maintains a single linked list of symspecs, +which will eventually get turned into 12 symbol tables, +organized into six include/exclude pairs - one +pair each for the flat profile (INCL_FLAT/EXCL_FLAT), +the call graph arcs (INCL_ARCS/EXCL_ARCS), +printing in the call graph (INCL_GRAPH/EXCL_GRAPH), +timing propagation in the call graph (INCL_TIME/EXCL_TIME), +the annotated source listing (INCL_ANNO/EXCL_ANNO), +and the execution count listing (INCL_EXEC/EXCL_EXEC). + +After option processing, @code{gprof} finishes +building the symspec list by adding all the symspecs in +@code{default_excluded_list} to the exclude lists +EXCL_TIME and EXCL_GRAPH, and if line-by-line profiling is specified, +EXCL_FLAT as well. +These default excludes are not added to EXCL_ANNO, EXCL_ARCS, and EXCL_EXEC. + +Next, the BFD library is called to open the object file, +verify that it is an object file, +and read its symbol table (@code{core.c:core_init}), +using @code{bfd_canonicalize_symtab} after mallocing +an appropiate sized array of asymbols. At this point, +function mappings are read (if the @samp{--file-ordering} option +has been specified), and the core text space is read into +memory (if the @samp{-c} option was given). + +@code{gprof}'s own symbol table, an array of Sym structures, +is now built. +This is done in one of two ways, by one of two routines, depending +on whether line-by-line profiling (@samp{-l} option) has been +enabled. +For normal profiling, the BFD canonical symbol table is scanned. +For line-by-line profiling, every +text space address is examined, and a new symbol table entry +gets created every time the line number changes. +In either case, two passes are made through the symbol +table - one to count the size of the symbol table required, +and the other to actually read the symbols. In between the +two passes, a single array of type @code{Sym} is created of +the appropiate length. +Finally, @code{symtab.c:symtab_finalize} +is called to sort the symbol table and remove duplicate entries +(entries with the same memory address). + +The symbol table must be a contiguous array for two reasons. +First, the @code{qsort} library function (which sorts an array) +will be used to sort the symbol table. +Also, the symbol lookup routine (@code{symtab.c:sym_lookup}), +which finds symbols +based on memory address, uses a binary search algorithm +which requires the symbol table to be a sorted array. +Function symbols are indicated with an @code{is_func} flag. +Line number symbols have no special flags set. +Additionally, a symbol can have an @code{is_static} flag +to indicate that it is a local symbol. + +With the symbol table read, the symspecs can now be translated +into Syms (@code{sym_ids.c:sym_id_parse}). Remember that a single +symspec can match multiple symbols. +An array of symbol tables +(@code{syms}) is created, each entry of which is a symbol table +of Syms to be included or excluded from a particular listing. +The master symbol table and the symspecs are examined by nested +loops, and every symbol that matches a symspec is inserted +into the appropriate syms table. This is done twice, once to +count the size of each required symbol table, and again to build +the tables, which have been malloced between passes. +From now on, to determine whether a symbol is on an include +or exclude symspec list, @code{gprof} simply uses its +standard symbol lookup routine on the appropriate table +in the @code{syms} array. + +Now the profile data file(s) themselves are read +(@code{gmon_io.c:gmon_out_read}), +first by checking for a new-style @samp{gmon.out} header, +then assuming this is an old-style BSD @samp{gmon.out} +if the magic number test failed. + +New-style histogram records are read by @code{hist.c:hist_read_rec}. +For the first histogram record, allocate a memory array to hold +all the bins, and read them in. +When multiple profile data files (or files with multiple histogram +records) are read, the starting address, ending address, number +of bins and sampling rate must match between the various histograms, +or a fatal error will result. +If everything matches, just sum the additional histograms into +the existing in-memory array. + +As each call graph record is read (@code{call_graph.c:cg_read_rec}), +the parent and child addresses +are matched to symbol table entries, and a call graph arc is +created by @code{cg_arcs.c:arc_add}, unless the arc fails a symspec +check against INCL_ARCS/EXCL_ARCS. As each arc is added, +a linked list is maintained of the parent's child arcs, and of the child's +parent arcs. +Both the child's call count and the arc's call count are +incremented by the record's call count. + +Basic-block records are read (@code{basic_blocks.c:bb_read_rec}), +but only if line-by-line profiling has been selected. +Each basic-block address is matched to a corresponding line +symbol in the symbol table, and an entry made in the symbol's +bb_addr and bb_calls arrays. Again, if multiple basic-block +records are present for the same address, the call counts +are cumulative. + +A gmon.sum file is dumped, if requested (@code{gmon_io.c:gmon_out_write}). + +If histograms were present in the data files, assign them to symbols +(@code{hist.c:hist_assign_samples}) by iterating over all the sample +bins and assigning them to symbols. Since the symbol table +is sorted in order of ascending memory addresses, we can +simple follow along in the symbol table as we make our pass +over the sample bins. +This step includes a symspec check against INCL_FLAT/EXCL_FLAT. +Depending on the histogram +scale factor, a sample bin may span multiple symbols, +in which case a fraction of the sample count is allocated +to each symbol, proportional to the degree of overlap. +This effect is rare for normal profiling, but overlaps +are more common during line-by-line profiling, and can +cause each of two adjacent lines to be credited with half +a hit, for example. + +If call graph data is present, @code{cg_arcs.c:cg_assemble} is called. +First, if @samp{-c} was specified, a machine-dependant +routine (@code{find_call}) scans through each symbol's machine code, +looking for subroutine call instructions, and adding them +to the call graph with a zero call count. +A topological sort is performed by depth-first numbering +all the symbols (@code{cg_dfn.c:cg_dfn}), so that +children are always numbered less than their parents, +then making a array of pointers into the symbol table and sorting it into +numerical order, which is reverse topological +order (children appear before parents). +Cycles are also detected at this point, all members +of which are assigned the same topological number. +Two passes are now made through this sorted array of symbol pointers. +The first pass, from end to beginning (parents to children), +computes the fraction of child time to propogate to each parent +and a print flag. +The print flag reflects symspec handling of INCL_GRAPH/EXCL_GRAPH, +with a parent's include or exclude (print or no print) property +being propagated to its children, unless they themselves explicitly appear +in INCL_GRAPH or EXCL_GRAPH. +A second pass, from beginning to end (children to parents) actually +propogates the timings along the call graph, subject +to a check against INCL_TIME/EXCL_TIME. +With the print flag, fractions, and timings now stored in the symbol +structures, the topological sort array is now discarded, and a +new array of pointers is assembled, this time sorted by propagated time. + +Finally, print the various outputs the user requested, which is now fairly +straightforward. The call graph (@code{cg_print.c:cg_print}) and +flat profile (@code{hist.c:hist_print}) are regurgitations of values +already computed. The annotated source listing +(@code{basic_blocks.c:print_annotated_source}) uses basic-block +information, if present, to label each line of code with call counts, +otherwise only the function call counts are presented. + +The function ordering code is marginally well documented +in the source code itself (@code{cg_print.c}). Basically, +the functions with the most use and the most parents are +placed first, followed by other functions with the most use, +followed by lower use functions, followed by unused functions +at the end. + +@node Debugging,,Internals,Details +@subsection Debugging @code{gprof} + +If @code{gprof} was compiled with debugging enabled, +the @samp{-d} option triggers debugging output +(to stdout) which can be helpful in understanding its operation. +The debugging number specified is interpreted as a sum of the following +options: + +@table @asis +@item 2 - Topological sort +Monitor depth-first numbering of symbols during call graph analysis +@item 4 - Cycles +Shows symbols as they are identified as cycle heads +@item 16 - Tallying +As the call graph arcs are read, show each arc and how +the total calls to each function are tallied +@item 32 - Call graph arc sorting +Details sorting individual parents/children within each call graph entry +@item 64 - Reading histogram and call graph records +Shows address ranges of histograms as they are read, and each +call graph arc +@item 128 - Symbol table +Reading, classifying, and sorting the symbol table from the object file. +For line-by-line profiling (@samp{-l} option), also shows line numbers +being assigned to memory addresses. +@item 256 - Static call graph +Trace operation of @samp{-c} option +@item 512 - Symbol table and arc table lookups +Detail operation of lookup routines +@item 1024 - Call graph propagation +Shows how function times are propagated along the call graph +@item 2048 - Basic-blocks +Shows basic-block records as they are read from profile data +(only meaningful with @samp{-l} option) +@item 4096 - Symspecs +Shows symspec-to-symbol pattern matching operation +@item 8192 - Annotate source +Tracks operation of @samp{-A} option +@end table --d debugging...? should this be documented? +@contents +@bye + +NEEDS AN INDEX -T - "traditional BSD style": How is it different? Should the differences be documented? -what is this about? (and to think, I *wrote* it...) - @item -c - The @samp{-c} option causes the static call-graph of the program to be - discovered by a heuristic which examines the text space of the object - file. Static-only parents or children are indicated with call counts of - @samp{0}. - example flat file adds up to 100.01%... note: time estimates now only go out to one decimal place (0.0), where |