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 }
`updcrc' has at least five basic-blocks. One is the function
itself. The `if' statement on line 9 generates two more basic-blocks,
one for each branch of the `if'. A fourth basic-block results from the
`if' on line 13, and the contents of the `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
`gprof -l -A'. The `-x' option is also helpful, to ensure that each
line of code is labeled at least once. Here is `updcrc''s annotated
source listing for a sample `gzip' run:
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 ->}
In this example, the function was called twice, passing once through
each branch of the `if' statement. The body of the `do' loop was
executed a total of 26312 times. Note how the `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.
File: gprof.info, Node: Inaccuracy, Next: How do I?, Prev: Output, Up: Top
6 Inaccuracy of `gprof' Output
******************************
* Menu:
* Sampling Error:: Statistical margins of error
* Assumptions:: Estimating children times
File: gprof.info, Node: Sampling Error, Next: Assumptions, Up: Inaccuracy
6.1 Statistical Sampling Error
==============================
The run-time figures that `gprof' gives you are based on a sampling
process, so they are subject to statistical inaccuracy. If a function
runs 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 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 and single
threaded. In multi-threaded applications, or single threaded
applications that link with multi-threaded libraries, the counts are
only deterministic if the counting function is thread-safe. (Note:
beware that the mcount counting function in glibc is _not_
thread-safe). *Note Implementation of Profiling: Implementation.
The "sampling period" that is printed at the beginning of the flat
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 can be predicted. For N samples, the
_expected_ error is the square-root of N. For example, if the sampling
period is 0.01 seconds and `foo''s run-time is 1 second, N is 100
samples (1 second/0.01 seconds), sqrt(N) is 10 samples, so the expected
error in `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 `bar''s run-time is 100 seconds, N is 10000 samples,
sqrt(N) is 100 samples, so the expected error in `bar''s run-time is 1
second, or one percent of the observed value. It is likely to vary
this much _on the average_ from one profiling run to the next.
(_Sometimes_ it will vary more.)
This does not mean that a small run-time figure is devoid of
information. If the program's _total_ run-time is large, a small
run-time for one function does tell you that that function used an
insignificant fraction of the whole program's time. Usually this means
it is not worth optimizing.
One way to get more accuracy is to give your program more (but
similar) input data so it will take longer. Another way is to combine
the data from several runs, using the `-s' option of `gprof'. Here is
how:
1. Run your program once.
2. Issue the command `mv gmon.out gmon.sum'.
3. Run your program again, the same as before.
4. Merge the new data in `gmon.out' into `gmon.sum' with this command:
gprof -s EXECUTABLE-FILE gmon.out gmon.sum
5. Repeat the last two steps as often as you wish.
6. Analyze the cumulative data using this command:
gprof EXECUTABLE-FILE gmon.sum > OUTPUT-FILE
File: gprof.info, Node: Assumptions, Prev: Sampling Error, Up: Inaccuracy
6.2 Estimating `children' Times
===============================
Some of the figures in the call graph are estimates--for example, the
`children' time values and all the time figures in caller and
subroutine lines.
There is no direct information about these measurements in the
profile data itself. Instead, `gprof' estimates them by making an
assumption about your program that might or might not be true.
The assumption made is that the average time spent in each call to
any function `foo' is not correlated with who called `foo'. If `foo'
used 5 seconds in all, and 2/5 of the calls to `foo' came from `a',
then `foo' contributes 2 seconds to `a''s `children' time, by
assumption.
This assumption is usually true enough, but for some programs it is
far from true. Suppose that `foo' returns very quickly when its
argument is zero; suppose that `a' always passes zero as an argument,
while other callers of `foo' pass other arguments. In this program,
all the time spent in `foo' is in the calls from callers other than `a'.
But `gprof' has no way of knowing this; it will blindly and incorrectly
charge 2 seconds of time in `foo' to the children of `a'.
We hope some day to put more complete data into `gmon.out', so that
this assumption is no longer needed, if we can figure out how. For the
novice, the estimated figures are usually more useful than misleading.
File: gprof.info, Node: How do I?, Next: Incompatibilities, Prev: Inaccuracy, Up: Top
7 Answers to Common Questions
*****************************
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 `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
artificial hot spots since compiling with `-pg' adds a significant
overhead to function calls. An alternative solution is to use a
non-intrusive profiler, e.g. oprofile.
How do I find which lines in my program were executed the most times?
Use the `gcov' program.
How do I find which lines in my program called a particular function?
Use `gprof -l' and lookup the function in the call graph. The
callers will be broken down by function and line number.
How do I analyze a program that runs for less than a second?
Try using a shell script like this one:
for i in `seq 1 100`; do
fastprog
mv gmon.out gmon.out.$i
done
gprof -s fastprog gmon.out.*
gprof fastprog gmon.sum
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).
File: gprof.info, Node: Incompatibilities, Next: Details, Prev: How do I?, Up: Top
8 Incompatibilities with Unix `gprof'
*************************************
GNU `gprof' and Berkeley Unix `gprof' use the same data file
`gmon.out', and provide essentially the same information. But there
are a few differences.
* GNU `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 `gprof' to easily identify new
style files. Old BSD-style files can still be read. *Note
Profiling Data File Format: File Format.
* For a recursive function, Unix `gprof' lists the function as a
parent and as a child, with a `calls' field that lists the number
of recursive calls. GNU `gprof' omits these lines and puts the
number of recursive calls in the primary line.
* When a function is suppressed from the call graph with `-e', GNU
`gprof' still lists it as a subroutine of functions that call it.
* GNU `gprof' accepts the `-k' with its argument in the form
`from/to', instead of `from to'.
* In the annotated source listing, if there are multiple basic
blocks on the same line, GNU `gprof' prints all of their counts,
separated by commas.
* The blurbs, field widths, and output formats are different. GNU
`gprof' prints blurbs after the tables, so that you can see the
tables without skipping the blurbs.
File: gprof.info, Node: Details, Next: GNU Free Documentation License, Prev: Incompatibilities, Up: Top
9 Details of Profiling
**********************
* Menu:
* Implementation:: How a program collects profiling information
* File Format:: Format of `gmon.out' files
* Internals:: `gprof''s internal operation
* Debugging:: Using `gprof''s `-d' option
File: gprof.info, Node: Implementation, Next: File Format, Up: Details
9.1 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 `-pg' option, which causes every function to call `mcount' (or
`_mcount', or `__mcount', depending on the OS and compiler) as one of
its first operations.
The `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-dependent operation, `mcount' itself is typically a short
assembly-language stub routine that extracts the required information,
and then calls `__mcount_internal' (a normal C function) with two
arguments--`frompc' and `selfpc'. `__mcount_internal' is responsible
for maintaining the in-memory call graph, which records `frompc',
`selfpc', and the number of times each of these call arcs was traversed.
GCC Version 2 provides a magical function
(`__builtin_return_address'), which allows a generic `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
`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 `-pg'. If
you link your program with `gcc ... -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.
This is done is one of two ways. Most UNIX-like operating systems
provide a `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 `profil()' system call. On such a system,
arrangements are made for the kernel to periodically deliver a signal
to the process (typically via `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 `profil()' or sets up a clock signal handler. This
routine (`monstartup') can be invoked in several ways. On Linux
systems, a special profiling startup file `gcrt0.o', which invokes
`monstartup' before `main', is used instead of the default `crt0.o'.
Use of this special startup file is one of the effects of using `gcc
... -pg' to link. On SPARC systems, no special startup files are used.
Rather, the `mcount' routine, when it is invoked for the first time
(typically when `main' is called), calls `monstartup'.
If the compiler's `-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 `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 (`mcleanup') which is
typically registered using `atexit()' to be called as the program
exits, and is responsible for writing the 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.
The output from `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 `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
`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.
File: gprof.info, Node: File Format, Next: Internals, Prev: Implementation, Up: Details
9.2 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. GNU `gprof'
uses a new file format that provides these features. For backward
compatibility, GNU `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 `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 target for which
the profile was collected. GNU `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, GNU `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.
9.2.1 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.
9.2.2 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.
9.2.3 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.
File: gprof.info, Node: Internals, Next: Debugging, Prev: File Format, Up: Details
9.3 `gprof''s Internal Operation
================================
Like most programs, `gprof' begins by processing its options. During
this stage, it may building its symspec list (`sym_ids.c:sym_id_add'),
if options are specified which use symspecs. `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, `gprof' finishes building the symspec list
by adding all the symspecs in `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 (`core.c:core_init'),
using `bfd_canonicalize_symtab' after mallocing an appropriately sized
array of symbols. At this point, function mappings are read (if the
`--file-ordering' option has been specified), and the core text space
is read into memory (if the `-c' option was given).
`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 (`-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 `Sym'
is created of the appropriate length. Finally,
`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 `qsort' library function (which sorts an array) will be used to
sort the symbol table. Also, the symbol lookup routine
(`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 `is_func' flag.
Line number symbols have no special flags set. Additionally, a symbol
can have an `is_static' flag to indicate that it is a local symbol.
With the symbol table read, the symspecs can now be translated into
Syms (`sym_ids.c:sym_id_parse'). Remember that a single symspec can
match multiple symbols. An array of symbol tables (`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, `gprof' simply uses its standard symbol lookup routine on the
appropriate table in the `syms' array.
Now the profile data file(s) themselves are read
(`gmon_io.c:gmon_out_read'), first by checking for a new-style
`gmon.out' header, then assuming this is an old-style BSD `gmon.out' if
the magic number test failed.
New-style histogram records are read by `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 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.
As each call graph record is read (`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 `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 (`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 (`gmon_io.c:gmon_out_write').
If histograms were present in the data files, assign them to symbols
(`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, `cg_arcs.c:cg_assemble' is called.
First, if `-c' was specified, a machine-dependent routine (`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 (`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 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.
Finally, print the various outputs the user requested, which is now
fairly straightforward. The call graph (`cg_print.c:cg_print') and
flat profile (`hist.c:hist_print') are regurgitations of values already
computed. The annotated source listing
(`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 (`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.
File: gprof.info, Node: Debugging, Prev: Internals, Up: Details
9.4 Debugging `gprof'
=====================
If `gprof' was compiled with debugging enabled, the `-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:
2 - Topological sort
Monitor depth-first numbering of symbols during call graph analysis
4 - Cycles
Shows symbols as they are identified as cycle heads
16 - Tallying
As the call graph arcs are read, show each arc and how the total
calls to each function are tallied
32 - Call graph arc sorting
Details sorting individual parents/children within each call graph
entry
64 - Reading histogram and call graph records
Shows address ranges of histograms as they are read, and each call
graph arc
128 - Symbol table
Reading, classifying, and sorting the symbol table from the object
file. For line-by-line profiling (`-l' option), also shows line
numbers being assigned to memory addresses.
256 - Static call graph
Trace operation of `-c' option
512 - Symbol table and arc table lookups
Detail operation of lookup routines
1024 - Call graph propagation
Shows how function times are propagated along the call graph
2048 - Basic-blocks
Shows basic-block records as they are read from profile data (only
meaningful with `-l' option)
4096 - Symspecs
Shows symspec-to-symbol pattern matching operation
8192 - Annotate source
Tracks operation of `-A' option
File: gprof.info, Node: GNU Free Documentation License, Prev: Details, Up: Top
Appendix A GNU Free Documentation License
*****************************************
Version 1.3, 3 November 2008
Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
`http://fsf.org/'
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
0. PREAMBLE
The purpose of this License is to make a manual, textbook, or other
functional and useful document "free" in the sense of freedom: to
assure everyone the effective freedom to copy and redistribute it,
with or without modifying it, either commercially or
noncommercially. Secondarily, this License preserves for the
author and publisher a way to get credit for their work, while not
being considered responsible for modifications made by others.
This License is a kind of "copyleft", which means that derivative
works of the document must themselves be free in the same sense.
It complements the GNU General Public License, which is a copyleft
license designed for free software.
We have designed this License in order to use it for manuals for
free software, because free software needs free documentation: a
free program should come with manuals providing the same freedoms
that the software does. But this License is not limited to
software manuals; it can be used for any textual work, regardless
of subject matter or whether it is published as a printed book.
We recommend this License principally for works whose purpose is
instruction or reference.
1. APPLICABILITY AND DEFINITIONS
This License applies to any manual or other work, in any medium,
that contains a notice placed by the copyright holder saying it
can be distributed under the terms of this License. Such a notice
grants a world-wide, royalty-free license, unlimited in duration,
to use that work under the conditions stated herein. The
"Document", below, refers to any such manual or work. Any member
of the public is a licensee, and is addressed as "you". You
accept the license if you copy, modify or distribute the work in a
way requiring permission under copyright law.
A "Modified Version" of the Document means any work containing the
Document or a portion of it, either copied verbatim, or with
modifications and/or translated into another language.
A "Secondary Section" is a named appendix or a front-matter section
of the Document that deals exclusively with the relationship of the
publishers or authors of the Document to the Document's overall
subject (or to related matters) and contains nothing that could
fall directly within that overall subject. (Thus, if the Document
is in part a textbook of mathematics, a Secondary Section may not
explain any mathematics.) The relationship could be a matter of
historical connection with the subject or with related matters, or
of legal, commercial, philosophical, ethical or political position
regarding them.
The "Invariant Sections" are certain Secondary Sections whose
titles are designated, as being those of Invariant Sections, in
the notice that says that the Document is released under this
License. If a section does not fit the above definition of
Secondary then it is not allowed to be designated as Invariant.
The Document may contain zero Invariant Sections. If the Document
does not identify any Invariant Sections then there are none.
The "Cover Texts" are certain short passages of text that are
listed, as Front-Cover Texts or Back-Cover Texts, in the notice
that says that the Document is released under this License. A
Front-Cover Text may be at most 5 words, and a Back-Cover Text may
be at most 25 words.
A "Transparent" copy of the Document means a machine-readable copy,
represented in a format whose specification is available to the
general public, that is suitable for revising the document
straightforwardly with generic text editors or (for images
composed of pixels) generic paint programs or (for drawings) some
widely available drawing editor, and that is suitable for input to
text formatters or for automatic translation to a variety of
formats suitable for input to text formatters. A copy made in an
otherwise Transparent file format whose markup, or absence of
markup, has been arranged to thwart or discourage subsequent
modification by readers is not Transparent. An image format is
not Transparent if used for any substantial amount of text. A
copy that is not "Transparent" is called "Opaque".
Examples of suitable formats for Transparent copies include plain
ASCII without markup, Texinfo input format, LaTeX input format,
SGML or XML using a publicly available DTD, and
standard-conforming simple HTML, PostScript or PDF designed for
human modification. Examples of transparent image formats include
PNG, XCF and JPG. Opaque formats include proprietary formats that
can be read and edited only by proprietary word processors, SGML or
XML for which the DTD and/or processing tools are not generally
available, and the machine-generated HTML, PostScript or PDF
produced by some word processors for output purposes only.
The "Title Page" means, for a printed book, the title page itself,
plus such following pages as are needed to hold, legibly, the
material this License requires to appear in the title page. For
works in formats which do not have any title page as such, "Title
Page" means the text near the most prominent appearance of the
work's title, preceding the beginning of the body of the text.
The "publisher" means any person or entity that distributes copies
of the Document to the public.
A section "Entitled XYZ" means a named subunit of the Document
whose title either is precisely XYZ or contains XYZ in parentheses
following text that translates XYZ in another language. (Here XYZ
stands for a specific section name mentioned below, such as
"Acknowledgements", "Dedications", "Endorsements", or "History".)
To "Preserve the Title" of such a section when you modify the
Document means that it remains a section "Entitled XYZ" according
to this definition.
The Document may include Warranty Disclaimers next to the notice
which states that this License applies to the Document. These
Warranty Disclaimers are considered to be included by reference in
this License, but only as regards disclaiming warranties: any other
implication that these Warranty Disclaimers may have is void and
has no effect on the meaning of this License.
2. VERBATIM COPYING
You may copy and distribute the Document in any medium, either
commercially or noncommercially, provided that this License, the
copyright notices, and the license notice saying this License
applies to the Document are reproduced in all copies, and that you
add no other conditions whatsoever to those of this License. You
may not use technical measures to obstruct or control the reading
or further copying of the copies you make or distribute. However,
you may accept compensation in exchange for copies. If you
distribute a large enough number of copies you must also follow
the conditions in section 3.
You may also lend copies, under the same conditions stated above,
and you may publicly display copies.
3. COPYING IN QUANTITY
If you publish printed copies (or copies in media that commonly
have printed covers) of the Document, numbering more than 100, and
the Document's license notice requires Cover Texts, you must
enclose the copies in covers that carry, clearly and legibly, all
these Cover Texts: Front-Cover Texts on the front cover, and
Back-Cover Texts on the back cover. Both covers must also clearly
and legibly identify you as the publisher of these copies. The
front cover must present the full title with all words of the
title equally prominent and visible. You may add other material
on the covers in addition. Copying with changes limited to the
covers, as long as they preserve the title of the Document and
satisfy these conditions, can be treated as verbatim copying in
other respects.
If the required texts for either cover are too voluminous to fit
legibly, you should put the first ones listed (as many as fit
reasonably) on the actual cover, and continue the rest onto
adjacent pages.
If you publish or distribute Opaque copies of the Document
numbering more than 100, you must either include a
machine-readable Transparent copy along with each Opaque copy, or
state in or with each Opaque copy a computer-network location from
which the general network-using public has access to download
using public-standard network protocols a complete Transparent
copy of the Document, free of added material. If you use the
latter option, you must take reasonably prudent steps, when you
begin distribution of Opaque copies in quantity, to ensure that
this Transparent copy will remain thus accessible at the stated
location until at least one year after the last time you
distribute an Opaque copy (directly or through your agents or
retailers) of that edition to the public.
It is requested, but not required, that you contact the authors of
the Document well before redistributing any large number of
copies, to give them a chance to provide you with an updated
version of the Document.
4. MODIFICATIONS
You may copy and distribute a Modified Version of the Document
under the conditions of sections 2 and 3 above, provided that you
release the Modified Version under precisely this License, with
the Modified Version filling the role of the Document, thus
licensing distribution and modification of the Modified Version to
whoever possesses a copy of it. In addition, you must do these
things in the Modified Version:
A. Use in the Title Page (and on the covers, if any) a title
distinct from that of the Document, and from those of
previous versions (which should, if there were any, be listed
in the History section of the Document). You may use the
same title as a previous version if the original publisher of
that version gives permission.
B. List on the Title Page, as authors, one or more persons or
entities responsible for authorship of the modifications in
the Modified Version, together with at least five of the
principal authors of the Document (all of its principal
authors, if it has fewer than five), unless they release you
from this requirement.
C. State on the Title page the name of the publisher of the
Modified Version, as the publisher.
D. Preserve all the copyright notices of the Document.
E. Add an appropriate copyright notice for your modifications
adjacent to the other copyright notices.
F. Include, immediately after the copyright notices, a license
notice giving the public permission to use the Modified
Version under the terms of this License, in the form shown in
the Addendum below.
G. Preserve in that license notice the full lists of Invariant
Sections and required Cover Texts given in the Document's
license notice.
H. Include an unaltered copy of this License.
I. Preserve the section Entitled "History", Preserve its Title,
and add to it an item stating at least the title, year, new
authors, and publisher of the Modified Version as given on
the Title Page. If there is no section Entitled "History" in
the Document, create one stating the title, year, authors,
and publisher of the Document as given on its Title Page,
then add an item describing the Modified Version as stated in
the previous sentence.
J. Preserve the network location, if any, given in the Document
for public access to a Transparent copy of the Document, and
likewise the network locations given in the Document for
previous versions it was based on. These may be placed in
the "History" section. You may omit a network location for a
work that was published at least four years before the
Document itself, or if the original publisher of the version
it refers to gives permission.
K. For any section Entitled "Acknowledgements" or "Dedications",
Preserve the Title of the section, and preserve in the
section all the substance and tone of each of the contributor
acknowledgements and/or dedications given therein.
L. Preserve all the Invariant Sections of the Document,
unaltered in their text and in their titles. Section numbers
or the equivalent are not considered part of the section
titles.
M. Delete any section Entitled "Endorsements". Such a section
may not be included in the Modified Version.
N. Do not retitle any existing section to be Entitled
"Endorsements" or to conflict in title with any Invariant
Section.
O. Preserve any Warranty Disclaimers.
If the Modified Version includes new front-matter sections or
appendices that qualify as Secondary Sections and contain no
material copied from the Document, you may at your option
designate some or all of these sections as invariant. To do this,
add their titles to the list of Invariant Sections in the Modified
Version's license notice. These titles must be distinct from any
other section titles.
You may add a section Entitled "Endorsements", provided it contains
nothing but endorsements of your Modified Version by various
parties--for example, statements of peer review or that the text
has been approved by an organization as the authoritative
definition of a standard.
You may add a passage of up to five words as a Front-Cover Text,
and a passage of up to 25 words as a Back-Cover Text, to the end
of the list of Cover Texts in the Modified Version. Only one
passage of Front-Cover Text and one of Back-Cover Text may be
added by (or through arrangements made by) any one entity. If the
Document already includes a cover text for the same cover,
previously added by you or by arrangement made by the same entity
you are acting on behalf of, you may not add another; but you may
replace the old one, on explicit permission from the previous
publisher that added the old one.
The author(s) and publisher(s) of the Document do not by this
License give permission to use their names for publicity for or to
assert or imply endorsement of any Modified Version.
5. COMBINING DOCUMENTS
You may combine the Document with other documents released under
this License, under the terms defined in section 4 above for
modified versions, provided that you include in the combination
all of the Invariant Sections of all of the original documents,
unmodified, and list them all as Invariant Sections of your
combined work in its license notice, and that you preserve all
their Warranty Disclaimers.
The combined work need only contain one copy of this License, and
multiple identical Invariant Sections may be replaced with a single
copy. If there are multiple Invariant Sections with the same name
but different contents, make the title of each such section unique
by adding at the end of it, in parentheses, the name of the
original author or publisher of that section if known, or else a
unique number. Make the same adjustment to the section titles in
the list of Invariant Sections in the license notice of the
combined work.
In the combination, you must combine any sections Entitled
"History" in the various original documents, forming one section
Entitled "History"; likewise combine any sections Entitled
"Acknowledgements", and any sections Entitled "Dedications". You
must delete all sections Entitled "Endorsements."
6. COLLECTIONS OF DOCUMENTS
You may make a collection consisting of the Document and other
documents released under this License, and replace the individual
copies of this License in the various documents with a single copy
that is included in the collection, provided that you follow the
rules of this License for verbatim copying of each of the
documents in all other respects.
You may extract a single document from such a collection, and
distribute it individually under this License, provided you insert
a copy of this License into the extracted document, and follow
this License in all other respects regarding verbatim copying of
that document.
7. AGGREGATION WITH INDEPENDENT WORKS
A compilation of the Document or its derivatives with other
separate and independent documents or works, in or on a volume of
a storage or distribution medium, is called an "aggregate" if the
copyright resulting from the compilation is not used to limit the
legal rights of the compilation's users beyond what the individual
works permit. When the Document is included in an aggregate, this
License does not apply to the other works in the aggregate which
are not themselves derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these
copies of the Document, then if the Document is less than one half
of the entire aggregate, the Document's Cover Texts may be placed
on covers that bracket the Document within the aggregate, or the
electronic equivalent of covers if the Document is in electronic
form. Otherwise they must appear on printed covers that bracket
the whole aggregate.
8. TRANSLATION
Translation is considered a kind of modification, so you may
distribute translations of the Document under the terms of section
4. Replacing Invariant Sections with translations requires special
permission from their copyright holders, but you may include
translations of some or all Invariant Sections in addition to the
original versions of these Invariant Sections. You may include a
translation of this License, and all the license notices in the
Document, and any Warranty Disclaimers, provided that you also
include the original English version of this License and the
original versions of those notices and disclaimers. In case of a
disagreement between the translation and the original version of
this License or a notice or disclaimer, the original version will
prevail.
If a section in the Document is Entitled "Acknowledgements",
"Dedications", or "History", the requirement (section 4) to
Preserve its Title (section 1) will typically require changing the
actual title.
9. TERMINATION
You may not copy, modify, sublicense, or distribute the Document
except as expressly provided under this License. Any attempt
otherwise to copy, modify, sublicense, or distribute it is void,
and will automatically terminate your rights under this License.
However, if you cease all violation of this License, then your
license from a particular copyright holder is reinstated (a)
provisionally, unless and until the copyright holder explicitly
and finally terminates your license, and (b) permanently, if the
copyright holder fails to notify you of the violation by some
reasonable means prior to 60 days after the cessation.
Moreover, your license from a particular copyright holder is
reinstated permanently if the copyright holder notifies you of the
violation by some reasonable means, this is the first time you have
received notice of violation of this License (for any work) from
that copyright holder, and you cure the violation prior to 30 days
after your receipt of the notice.
Termination of your rights under this section does not terminate
the licenses of parties who have received copies or rights from
you under this License. If your rights have been terminated and
not permanently reinstated, receipt of a copy of some or all of
the same material does not give you any rights to use it.
10. FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions of
the GNU Free Documentation License from time to time. Such new
versions will be similar in spirit to the present version, but may
differ in detail to address new problems or concerns. See
`http://www.gnu.org/copyleft/'.
Each version of the License is given a distinguishing version
number. If the Document specifies that a particular numbered
version of this License "or any later version" applies to it, you
have the option of following the terms and conditions either of
that specified version or of any later version that has been
published (not as a draft) by the Free Software Foundation. If
the Document does not specify a version number of this License,
you may choose any version ever published (not as a draft) by the
Free Software Foundation. If the Document specifies that a proxy
can decide which future versions of this License can be used, that
proxy's public statement of acceptance of a version permanently
authorizes you to choose that version for the Document.
11. RELICENSING
"Massive Multiauthor Collaboration Site" (or "MMC Site") means any
World Wide Web server that publishes copyrightable works and also
provides prominent facilities for anybody to edit those works. A
public wiki that anybody can edit is an example of such a server.
A "Massive Multiauthor Collaboration" (or "MMC") contained in the
site means any set of copyrightable works thus published on the MMC
site.
"CC-BY-SA" means the Creative Commons Attribution-Share Alike 3.0
license published by Creative Commons Corporation, a not-for-profit
corporation with a principal place of business in San Francisco,
California, as well as future copyleft versions of that license
published by that same organization.
"Incorporate" means to publish or republish a Document, in whole or
in part, as part of another Document.
An MMC is "eligible for relicensing" if it is licensed under this
License, and if all works that were first published under this
License somewhere other than this MMC, and subsequently
incorporated in whole or in part into the MMC, (1) had no cover
texts or invariant sections, and (2) were thus incorporated prior
to November 1, 2008.
The operator of an MMC Site may republish an MMC contained in the
site under CC-BY-SA on the same site at any time before August 1,
2009, provided the MMC is eligible for relicensing.
ADDENDUM: How to use this License for your documents
====================================================
To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and license
notices just after the title page:
Copyright (C) YEAR YOUR NAME.
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, no Front-Cover Texts, and no Back-Cover
Texts. A copy of the license is included in the section entitled ``GNU
Free Documentation License''.
If you have Invariant Sections, Front-Cover Texts and Back-Cover
Texts, replace the "with...Texts." line with this:
with the Invariant Sections being LIST THEIR TITLES, with
the Front-Cover Texts being LIST, and with the Back-Cover Texts
being LIST.
If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.
If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License, to
permit their use in free software.
Tag Table:
Node: Top777
Node: Introduction2100
Node: Compiling4592
Node: Executing8648
Node: Invoking11436
Node: Output Options12851
Node: Analysis Options19940
Node: Miscellaneous Options23638
Node: Deprecated Options24893
Node: Symspecs26962
Node: Output28788
Node: Flat Profile29828
Node: Call Graph34781
Node: Primary38013
Node: Callers40601
Node: Subroutines42718
Node: Cycles44559
Node: Line-by-line51336
Node: Annotated Source55409
Node: Inaccuracy58408
Node: Sampling Error58666
Node: Assumptions61570
Node: How do I?63040
Node: Incompatibilities64594
Node: Details66088
Node: Implementation66481
Node: File Format72378
Node: Internals76668
Node: Debugging85163
Node: GNU Free Documentation License86764
End Tag Table
���������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������This is binutils.info, produced by makeinfo version 4.8 from
binutils.texi.
Copyright (C) 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 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".
INFO-DIR-SECTION Software development
START-INFO-DIR-ENTRY
* Binutils: (binutils). The GNU binary utilities.
END-INFO-DIR-ENTRY
INFO-DIR-SECTION Individual utilities
START-INFO-DIR-ENTRY
* addr2line: (binutils)addr2line. Convert addresses to file and line.
* ar: (binutils)ar. Create, modify, and extract from archives.
* c++filt: (binutils)c++filt. Filter to demangle encoded C++ symbols.
* cxxfilt: (binutils)c++filt. MS-DOS name for c++filt.
* dlltool: (binutils)dlltool. Create files needed to build and use DLLs.
* nlmconv: (binutils)nlmconv. Converts object code into an NLM.
* nm: (binutils)nm. List symbols from object files.
* objcopy: (binutils)objcopy. Copy and translate object files.
* objdump: (binutils)objdump. Display information from object files.
* ranlib: (binutils)ranlib. Generate index to archive contents.
* readelf: (binutils)readelf. Display the contents of ELF format files.
* size: (binutils)size. List section sizes and total size.
* strings: (binutils)strings. List printable strings from files.
* strip: (binutils)strip. Discard symbols.
* elfedit: (binutils)elfedit. Update the ELF header of ELF files.
* windmc: (binutils)windmc. Generator for Windows message resources.
* windres: (binutils)windres. Manipulate Windows resources.
END-INFO-DIR-ENTRY
File: binutils.info, Node: Top, Next: ar, Up: (dir)
Introduction
************
This brief manual contains documentation for the GNU binary utilities
(GNU Binutils) version 2.21:
This document is distributed under the terms of the GNU Free
Documentation License version 1.3. A copy of the license is included
in the section entitled "GNU Free Documentation License".
* Menu:
* ar:: Create, modify, and extract from archives
* nm:: List symbols from object files
* objcopy:: Copy and translate object files
* objdump:: Display information from object files
* ranlib:: Generate index to archive contents
* readelf:: Display the contents of ELF format files
* size:: List section sizes and total size
* strings:: List printable strings from files
* strip:: Discard symbols
* elfedit:: Update the ELF header of ELF files
* c++filt:: Filter to demangle encoded C++ symbols
* cxxfilt: c++filt. MS-DOS name for c++filt
* addr2line:: Convert addresses to file and line
* nlmconv:: Converts object code into an NLM
* windres:: Manipulate Windows resources
* windmc:: Generator for Windows message resources
* dlltool:: Create files needed to build and use DLLs
* Common Options:: Command-line options for all utilities
* Selecting the Target System:: How these utilities determine the target
* Reporting Bugs:: Reporting Bugs
* GNU Free Documentation License:: GNU Free Documentation License
* Binutils Index:: Binutils Index
File: binutils.info, Node: ar, Next: nm, Prev: Top, Up: Top
1 ar
****
ar [`--plugin' NAME] [-]P[MOD [RELPOS] [COUNT]] ARCHIVE [MEMBER...]
ar -M [ <mri-script ]
The GNU `ar' program creates, modifies, and extracts from archives.
An "archive" is a single file holding a collection of other files in a
structure that makes it possible to retrieve the original individual
files (called "members" of the archive).
The original files' contents, mode (permissions), timestamp, owner,
and group are preserved in the archive, and can be restored on
extraction.
GNU `ar' can maintain archives whose members have names of any
length; however, depending on how `ar' is configured on your system, a
limit on member-name length may be imposed for compatibility with
archive formats maintained with other tools. If it exists, the limit
is often 15 characters (typical of formats related to a.out) or 16
characters (typical of formats related to coff).
`ar' is considered a binary utility because archives of this sort
are most often used as "libraries" holding commonly needed subroutines.
`ar' creates an index to the symbols defined in relocatable object
modules in the archive when you specify the modifier `s'. Once
created, this index is updated in the archive whenever `ar' makes a
change to its contents (save for the `q' update operation). An archive
with such an index speeds up linking to the library, and allows
routines in the library to call each other without regard to their
placement in the archive.
You may use `nm -s' or `nm --print-armap' to list this index table.
If an archive lacks the table, another form of `ar' called `ranlib' can
be used to add just the table.
GNU `ar' can optionally create a _thin_ archive, which contains a
symbol index and references to the original copies of the member files
of the archives. Such an archive is useful for building libraries for
use within a local build, where the relocatable objects are expected to
remain available, and copying the contents of each object would only
waste time and space. Thin archives are also _flattened_, so that
adding one or more archives to a thin archive will add the elements of
the nested archive individually. The paths to the elements of the
archive are stored relative to the archive itself.
GNU `ar' is designed to be compatible with two different facilities.
You can control its activity using command-line options, like the
different varieties of `ar' on Unix systems; or, if you specify the
single command-line option `-M', you can control it with a script
supplied via standard input, like the MRI "librarian" program.
* Menu:
* ar cmdline:: Controlling `ar' on the command line
* ar scripts:: Controlling `ar' with a script
File: binutils.info, Node: ar cmdline, Next: ar scripts, Up: ar
1.1 Controlling `ar' on the Command Line
========================================
ar [`--plugin' NAME] [`-X32_64'] [`-']P[MOD [RELPOS] [COUNT]] ARCHIVE [MEMBER...]
When you use `ar' in the Unix style, `ar' insists on at least two
arguments to execute: one keyletter specifying the _operation_
(optionally accompanied by other keyletters specifying _modifiers_),
and the archive name to act on.
Most operations can also accept further MEMBER arguments, specifying
particular files to operate on.
GNU `ar' allows you to mix the operation code P and modifier flags
MOD in any order, within the first command-line argument.
If you wish, you may begin the first command-line argument with a
dash.
The P keyletter specifies what operation to execute; it may be any
of the following, but you must specify only one of them:
`d'
_Delete_ modules from the archive. Specify the names of modules to
be deleted as MEMBER...; the archive is untouched if you specify
no files to delete.
If you specify the `v' modifier, `ar' lists each module as it is
deleted.
`m'
Use this operation to _move_ members in an archive.
The ordering of members in an archive can make a difference in how
programs are linked using the library, if a symbol is defined in
more than one member.
If no modifiers are used with `m', any members you name in the
MEMBER arguments are moved to the _end_ of the archive; you can
use the `a', `b', or `i' modifiers to move them to a specified
place instead.
`p'
_Print_ the specified members of t