253 lines
12 KiB
HTML
253 lines
12 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
|
<html>
|
|
<!-- This file documents the gprof profiler of the GNU system.
|
|
|
|
Copyright (C) 1988-2016 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 1.3
|
|
or any later version published by the Free Software Foundation;
|
|
with no Invariant Sections, with no Front-Cover Texts, and with no
|
|
Back-Cover Texts. A copy of the license is included in the
|
|
section entitled "GNU Free Documentation License".
|
|
-->
|
|
<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
|
|
<head>
|
|
<title>GNU gprof: Internals</title>
|
|
|
|
<meta name="description" content="GNU gprof: Internals">
|
|
<meta name="keywords" content="GNU gprof: Internals">
|
|
<meta name="resource-type" content="document">
|
|
<meta name="distribution" content="global">
|
|
<meta name="Generator" content="makeinfo">
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
|
<link href="index.html#Top" rel="start" title="Top">
|
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
|
<link href="Details.html#Details" rel="up" title="Details">
|
|
<link href="Debugging.html#Debugging" rel="next" title="Debugging">
|
|
<link href="File-Format.html#File-Format" rel="prev" title="File Format">
|
|
<style type="text/css">
|
|
<!--
|
|
a.summary-letter {text-decoration: none}
|
|
blockquote.smallquotation {font-size: smaller}
|
|
div.display {margin-left: 3.2em}
|
|
div.example {margin-left: 3.2em}
|
|
div.indentedblock {margin-left: 3.2em}
|
|
div.lisp {margin-left: 3.2em}
|
|
div.smalldisplay {margin-left: 3.2em}
|
|
div.smallexample {margin-left: 3.2em}
|
|
div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
|
|
div.smalllisp {margin-left: 3.2em}
|
|
kbd {font-style:oblique}
|
|
pre.display {font-family: inherit}
|
|
pre.format {font-family: inherit}
|
|
pre.menu-comment {font-family: serif}
|
|
pre.menu-preformatted {font-family: serif}
|
|
pre.smalldisplay {font-family: inherit; font-size: smaller}
|
|
pre.smallexample {font-size: smaller}
|
|
pre.smallformat {font-family: inherit; font-size: smaller}
|
|
pre.smalllisp {font-size: smaller}
|
|
span.nocodebreak {white-space:nowrap}
|
|
span.nolinebreak {white-space:nowrap}
|
|
span.roman {font-family:serif; font-weight:normal}
|
|
span.sansserif {font-family:sans-serif; font-weight:normal}
|
|
ul.no-bullet {list-style: none}
|
|
-->
|
|
</style>
|
|
|
|
|
|
</head>
|
|
|
|
<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
|
|
<a name="Internals"></a>
|
|
<div class="header">
|
|
<p>
|
|
Next: <a href="Debugging.html#Debugging" accesskey="n" rel="next">Debugging</a>, Previous: <a href="File-Format.html#File-Format" accesskey="p" rel="prev">File Format</a>, Up: <a href="Details.html#Details" accesskey="u" rel="up">Details</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p>
|
|
</div>
|
|
<hr>
|
|
<a name="gprof_0027s-Internal-Operation"></a>
|
|
<h3 class="section">9.3 <code>gprof</code>’s Internal Operation</h3>
|
|
|
|
<p>Like most programs, <code>gprof</code> begins by processing its options.
|
|
During this stage, it may building its symspec list
|
|
(<code>sym_ids.c:sym_id_add</code>), if
|
|
options are specified which use symspecs.
|
|
<code>gprof</code> 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).
|
|
</p>
|
|
<p>After option processing, <code>gprof</code> finishes
|
|
building the symspec list by adding all the symspecs in
|
|
<code>default_excluded_list</code> 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.
|
|
</p>
|
|
<p>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</code>),
|
|
using <code>bfd_canonicalize_symtab</code> after mallocing
|
|
an appropriately sized array of symbols. At this point,
|
|
function mappings are read (if the ‘<samp>--file-ordering</samp>’ option
|
|
has been specified), and the core text space is read into
|
|
memory (if the ‘<samp>-c</samp>’ option was given).
|
|
</p>
|
|
<p><code>gprof</code>’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</samp>’ 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</code> is created of
|
|
the appropriate length.
|
|
Finally, <code>symtab.c:symtab_finalize</code>
|
|
is called to sort the symbol table and remove duplicate entries
|
|
(entries with the same memory address).
|
|
</p>
|
|
<p>The symbol table must be a contiguous array for two reasons.
|
|
First, the <code>qsort</code> library function (which sorts an array)
|
|
will be used to sort the symbol table.
|
|
Also, the symbol lookup routine (<code>symtab.c:sym_lookup</code>),
|
|
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</code> flag.
|
|
Line number symbols have no special flags set.
|
|
Additionally, a symbol can have an <code>is_static</code> flag
|
|
to indicate that it is a local symbol.
|
|
</p>
|
|
<p>With the symbol table read, the symspecs can now be translated
|
|
into Syms (<code>sym_ids.c:sym_id_parse</code>). Remember that a single
|
|
symspec can match multiple symbols.
|
|
An array of symbol tables
|
|
(<code>syms</code>) 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</code> simply uses its
|
|
standard symbol lookup routine on the appropriate table
|
|
in the <code>syms</code> array.
|
|
</p>
|
|
<p>Now the profile data file(s) themselves are read
|
|
(<code>gmon_io.c:gmon_out_read</code>),
|
|
first by checking for a new-style ‘<samp>gmon.out</samp>’ header,
|
|
then assuming this is an old-style BSD ‘<samp>gmon.out</samp>’
|
|
if the magic number test failed.
|
|
</p>
|
|
<p>New-style histogram records are read by <code>hist.c:hist_read_rec</code>.
|
|
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 memory ranges of each pair of histogram records
|
|
must be either equal, or non-overlapping. For each pair of histogram
|
|
records, the resolution (memory region size divided by the number of
|
|
bins) must be the same. The time unit must be the same for all
|
|
histogram records. If the above containts are met, all histograms
|
|
for the same memory range are merged.
|
|
</p>
|
|
<p>As each call graph record is read (<code>call_graph.c:cg_read_rec</code>),
|
|
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</code>, 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.
|
|
</p>
|
|
<p>Basic-block records are read (<code>basic_blocks.c:bb_read_rec</code>),
|
|
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.
|
|
</p>
|
|
<p>A gmon.sum file is dumped, if requested (<code>gmon_io.c:gmon_out_write</code>).
|
|
</p>
|
|
<p>If histograms were present in the data files, assign them to symbols
|
|
(<code>hist.c:hist_assign_samples</code>) 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.
|
|
</p>
|
|
<p>If call graph data is present, <code>cg_arcs.c:cg_assemble</code> is called.
|
|
First, if ‘<samp>-c</samp>’ was specified, a machine-dependent
|
|
routine (<code>find_call</code>) 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</code>), 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 propagate 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
|
|
propagates 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.
|
|
</p>
|
|
<p>Finally, print the various outputs the user requested, which is now fairly
|
|
straightforward. The call graph (<code>cg_print.c:cg_print</code>) and
|
|
flat profile (<code>hist.c:hist_print</code>) are regurgitations of values
|
|
already computed. The annotated source listing
|
|
(<code>basic_blocks.c:print_annotated_source</code>) uses basic-block
|
|
information, if present, to label each line of code with call counts,
|
|
otherwise only the function call counts are presented.
|
|
</p>
|
|
<p>The function ordering code is marginally well documented
|
|
in the source code itself (<code>cg_print.c</code>). 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.
|
|
</p>
|
|
<hr>
|
|
<div class="header">
|
|
<p>
|
|
Next: <a href="Debugging.html#Debugging" accesskey="n" rel="next">Debugging</a>, Previous: <a href="File-Format.html#File-Format" accesskey="p" rel="prev">File Format</a>, Up: <a href="Details.html#Details" accesskey="u" rel="up">Details</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p>
|
|
</div>
|
|
|
|
|
|
|
|
</body>
|
|
</html>
|