gprof/README

   1                 README for GPROF
   2
   3 This is the GNU profiler.  It is distributed with other "binary
   4 utilities" which should be in ../binutils.  See ../binutils/README for
   5 more general notes, including where to send bug reports.
   6
   7 This file documents the changes and new features available with this
   8 version of GNU gprof.
   9
  10 * New Features
  11
  12  o Long options
  13
  14  o Supports generalized file format, without breaking backward compatibility:
  15    new file format supports basic-block execution counts and non-realtime
  16    histograms (see below)
  17
  18  o Supports profiling at the line level: flat profiles, call-graph profiles,
  19    and execution-counts can all be displayed at a level that identifies
  20    individual lines rather than just functions
  21
  22  o Test-coverage support (similar to Sun tcov program): source files
  23    can be annotated with the number of times a function was invoked
  24    or with the number of times each basic-block in a function was
  25    executed
  26
  27  o Generalized histograms: not just execution-time, but arbitrary
  28    histograms are support (for example, performance counter based
  29    profiles)
  30
  31  o Powerful mechanism to select data to be included/excluded from
  32    analysis and/or output
  33
  34  o Support for DEC OSF/1 v3.0
  35
  36  o Full cross-platform profiling support: gprof uses BFD to support
  37    arbitrary, non-native object file formats and non-native byte-orders
  38    (this feature has not been tested yet)
  39
  40  o In the call-graph function index, static function names are now
  41    printed together with the filename in which the function was defined
  42    (required bfd_find_nearest_line() support and symbolic debugging
  43     information to be present in the executable file)
  44
  45  o Major overhaul of source code (compiles cleanly with -Wall, etc.)
  46
  47 * Supported Platforms
  48
  49 The current version is known to work on:
  50
  51  o DEC OSF/1 v3.0
  52         All features supported.
  53
  54  o SunOS 4.1.x
  55         All features supported.
  56
  57  o Solaris 2.3
  58         Line-level profiling unsupported because bfd_find_nearest_line()
  59         is not fully implemented for Elf binaries.
  60
  61  o HP-UX 9.01
  62         Line-level profiling unsupported because bfd_find_nearest_line()
  63         is not fully implemented for SOM binaries.
  64
  65 * Detailed Description
  66
  67 ** User Interface Changes
  68
  69 The command-line interface is backwards compatible with earlier
  70 versions of GNU gprof and Berkeley gprof.  The only exception is
  71 the option to delete arcs from the call graph.  The old syntax
  72 was:
  73
  74         -k fromname toname
  75
  76 while the new syntax is:
  77
  78         -k fromname/toname
  79
  80 This change was necessary to be compatible with long-option parsing.
  81 Also, "fromname" and "toname" can now be arbitrary symspecs rather
  82 than just function names (see below for an explanation of symspecs).
  83 For example, option "-k gprof.c/" suppresses all arcs due to calls out
  84 of file "gprof.c".
  85
  86 *** Sym Specs
  87
  88 It is often necessary to apply gprof only to specific parts of a
  89 program.  GNU gprof has a simple but powerful mechanism to achieve
  90 this.  So called {\em symspecs\/} provide the foundation for this
  91 mechanism.  A symspec selects the parts of a profiled program to which
  92 an operation should be applied to.  The syntax of a symspec is
  93 simple:
  94
  95           filename_containing_a_dot
  96         | funcname_not_containing_a_dot
  97         | linenumber
  98         | ( [ any_filename ] `:' ( any_funcname | linenumber ) )
  99
 100 Here are some examples:
 101
 102         main.c                  Selects everything in file "main.c"---the
 103                                 dot in the string tells gprof to interpret
 104                                 the string as a filename, rather than as
 105                                 a function name.  To select a file whose
 106                                 name does contain a dot, a trailing colon
 107                                 should be specified.  For example, "odd:" is
 108                                 interpreted as the file named "odd".
 109
 110         main                    Selects all functions named "main".  Notice
 111                                 that there may be multiple instances of the
 112                                 same function name because some of the
 113                                 definitions may be local (i.e., static).
 114                                 Unless a function name is unique in a program,
 115                                 you must use the colon notation explained
 116                                 below to specify a function from a specific
 117                                 source file.  Sometimes, functionnames contain
 118                                 dots.  In such cases, it is necessary to
 119                                 add a leading colon to the name.  For example,
 120                                 ":.mul" selects function ".mul".
 121
 122         main.c:main             Selects function "main" in file "main.c".
 123
 124         main.c:134              Selects line 134 in file "main.c".
 125
 126 IMPLEMENTATION NOTE: The source code uses the type sym_id for symspecs.
 127 At some point, this probably ought to be changed to "sym_spec" to make
 128 reading the code easier.
 129
 130 *** Long options
 131
 132 GNU gprof now supports long options.  The following is a list of all
 133 supported options.  Options that are listed without description
 134 operate in the same manner as the corresponding option in older
 135 versions of gprof.
 136
 137 Short Form:     Long Form:
 138 -----------     ----------
 139 -l              --line
 140                         Request profiling at the line-level rather
 141                         than just at the function level.  Source
 142                         lines are identified by symbols of the form:
 143
 144                                 func (file:line)
 145
 146                         where "func" is the function name, "file" is the
 147                         file name and "line" is the line-number that
 148                         corresponds to the line.
 149
 150                         To work properly, the binary must contain symbolic
 151                         debugging information.  This means that the source
 152                         have to be translated with option "-g" specified.
 153                         Functions for which there is no symbolic debugging
 154                         information available are treated as if "--line"
 155                         had not been specified.  However, the line number
 156                         printed with such symbols is usually incorrect
 157                         and should be ignored.
 158
 159 -a              --no-static
 160 -A[symspec]     --annotated-source[=symspec]
 161                         Request output in the form of annotated source
 162                         files.  If "symspec" is specified, print output only
 163                         for symbols selected by "symspec".  If the option
 164                         is specified multiple times, annotated output is
 165                         generated for the union of all symspecs.
 166
 167                         Examples:
 168
 169                           -A            Prints annotated source for all
 170                                         source files.
 171                           -Agprof.c     Prints annotated source for file
 172                                         gprof.c.
 173                           -Afoobar      Prints annotated source for files
 174                                         containing a function named "foobar".
 175                                         The entire file will be printed, but
 176                                         only the function itself will be
 177                                         annotated with profile data.
 178
 179 -J[symspec]     --no-annotated-source[=symspec]
 180                         Suppress annotated source output.  If specified
 181                         without argument, annotated output is suppressed
 182                         completely.  With an argument, annotated output
 183                         is suppressed only for the symbols selected by
 184                         "symspec".  If the option is specified multiple
 185                         times, annotated output is suppressed for the
 186                         union of all symspecs.  This option has lower
 187                         precedence than --annotated-source
 188
 189 -p[symspec]     --flat-profile[=symspec]
 190                         Request output in the form of a flat profile
 191                         (unless any other output-style option is specified,
 192                          this option is turned on by default).  If
 193                         "symspec" is specified, include only symbols
 194                         selected by "symspec" in flat profile.  If the
 195                         option is specified multiple times, the flat
 196                         profile includes symbols selected by the union
 197                         of all symspecs.
 198
 199 -P[symspec]     --no-flat-profile[=symspec]
 200                         Suppress output in the flat profile.  If given
 201                         without an argument, the flat profile is suppressed
 202                         completely.  If "symspec" is specified, suppress
 203                         the selected symbols in the flat profile.  If the
 204                         option is specified multiple times, the union of
 205                         the selected symbols is suppressed.  This option
 206                         has lower precedence than --flat-profile.
 207
 208 -q[symspec]     --graph[=symspec]
 209                         Request output in the form of a call-graph
 210                         (unless any other output-style option is specified,
 211                          this option is turned on by default).  If "symspec"
 212                         is specified, include only symbols selected by
 213                         "symspec" in the call-graph.  If the option is
 214                         specified multiple times, the call-graph includes
 215                         symbols selected by the union of all symspecs.
 216
 217 -Q[symspec]     --no-graph[=symspec]
 218                         Suppress output in the call-graph.  If given without
 219                         an argument, the call-graph is suppressed completely.
 220                         With a "symspec", suppress the selected symbols
 221                         from the call-graph.  If the option is specified
 222                         multiple times, the union of the selected symbols
 223                         is suppressed.  This option has lower precedence
 224                         than --graph.
 225
 226 -C[symspec]     --exec-counts[=symspec]
 227                         Request output in the form of execution counts.
 228                         If "symspec" is present, include only symbols
 229                         selected by "symspec" in the execution count
 230                         listing.  If the option is specified multiple
 231                         times, the execution count listing includes
 232                         symbols selected by the union of all symspecs.
 233
 234 -Z[symspec]     --no-exec-counts[=symspec]
 235                         Suppress output in the execution count listing.
 236                         If given without an argument, the listing is
 237                         suppressed completely.  With a "symspec", suppress
 238                         the selected symbols from the call-graph.  If the
 239                         option is specified multiple times, the union of
 240                         the selected symbols is suppressed.  This option
 241                         has lower precedence than --exec-counts.
 242
 243 -i              --file-info
 244                         Print information about the profile files that
 245                         are read.  The information consists of the
 246                         number and types of records present in the
 247                         profile file.  Currently, a profile file can
 248                         contain any number and any combination of histogram,
 249                         call-graph, or basic-block count records.
 250
 251 -s              --sum
 252
 253 -x              --all-lines
 254                         This option affects annotated source output only.
 255                         By default, only the lines at the beginning of
 256                         a basic-block are annotated.  If this option is
 257                         specified, every line in a basic-block is annotated
 258                         by repeating the annotation for the first line.
 259                         This option is identical to tcov's "-a".
 260
 261 -I dirs         --directory-path=dirs
 262                         This option affects annotated source output only.
 263                         Specifies the list of directories to be searched
 264                         for source files.  The argument "dirs" is a colon
 265                         separated list of directories.  By default, gprof
 266                         searches for source files relative to the current
 267                         working directory only.
 268
 269 -z              --display-unused-functions
 270
 271 -m num          --min-count=num
 272                         This option affects annotated source and execution
 273                         count output only.  Symbols that are executed
 274                         less than "num" times are suppressed.  For annotated
 275                         source output, suppressed symbols are marked
 276                         by five hash-marks (#####).  In an execution count
 277                         output, suppressed symbols do not appear at all.
 278
 279 -L              --print-path
 280                         Normally, source filenames are printed with the path
 281                         component suppressed.  With this option, gprof
 282                         can be forced to print the full pathname of
 283                         source filenames.  The full pathname is determined
 284                         from symbolic debugging information in the image file
 285                         and is relative to the directory in which the compiler
 286                         was invoked.
 287
 288 -y              --separate-files
 289                         This option affects annotated source output only.
 290                         Normally, gprof prints annotated source files
 291                         to standard-output.  If this option is specified,
 292                         annotated source for a file named "path/filename"
 293                         is generated in the file "filename-ann".  That is,
 294                         annotated output is {\em always\/} generated in
 295                         gprof's current working directory.  Care has to
 296                         be taken if a program consists of files that have
 297                         identical filenames, but distinct paths.
 298
 299 -c              --static-call-graph
 300
 301 -t num          --table-length=num
 302                         This option affects annotated source output only.
 303                         After annotating a source file, gprof generates
 304                         an execution count summary consisting of a table
 305                         of lines with the top execution counts.  By
 306                         default, this table is ten entries long.
 307                         This option can be used to change the table length
 308                         or, by specifying an argument value of 0, it can be
 309                         suppressed completely.
 310
 311 -n symspec      --time=symspec
 312                         Only symbols selected by "symspec" are considered
 313                         in total and percentage time computations.
 314                         However, this option does not affect percentage time
 315                         computation for the flat profile.
 316                         If the option is specified multiple times, the union
 317                         of all selected symbols is used in time computations.
 318
 319 -N              --no-time=symspec
 320                         Exclude the symbols selected by "symspec" from
 321                         total and percentage time computations.
 322                         However, this option does not affect percentage time
 323                         computation for the flat profile.
 324                         This option is ignored if any --time options are
 325                         specified.
 326
 327 -w num          --width=num
 328                         Sets the output line width.  Currently, this option
 329                         affects the printing of the call-graph function index
 330                         only.
 331
 332 -e              <no long form---for backwards compatibility only>
 333 -E              <no long form---for backwards compatibility only>
 334 -f              <no long form---for backwards compatibility only>
 335 -F              <no long form---for backwards compatibility only>
 336 -k              <no long form---for backwards compatibility only>
 337 -b              --brief
 338 -dnum           --debug[=num]
 339
 340 -h              --help
 341                         Prints a usage message.
 342
 343 -O name         --file-format=name
 344                         Selects the format of the profile data files.
 345                         Recognized formats are "auto", "bsd", "magic",
 346                         and "prof".  The last one is not yet supported.
 347                         Format "auto" attempts to detect the file format
 348                         automatically (this is the default behavior).
 349                         It attempts to read the profile data files as
 350                         "magic" files and if this fails, falls back to
 351                         the "bsd" format.  "bsd" forces gprof to read
 352                         the data files in the BSD format.  "magic" forces
 353                         gprof to read the data files in the "magic" format.
 354
 355 -T              --traditional
 356 -v              --version
 357
 358 ** File Format Changes
 359
 360 The old BSD-derived format used for profile data does not contain a
 361 magic cookie that allows to check whether a data file really is a
 362 gprof file.  Furthermore, it does not provide a version number, thus
 363 rendering changes to the file format almost impossible.  GNU gprof
 364 uses a new file format that provides these features.  For backward
 365 compatibility, GNU gprof continues to support the old BSD-derived
 366 format, but not all features are supported with it.  For example,
 367 basic-block execution counts cannot be accommodated by the old file
 368 format.
 369
 370 The new file format is defined in header file \file{gmon_out.h}.  It
 371 consists of a header containing the magic cookie and a version number,
 372 as well as some spare bytes available for future extensions.  All data
 373 in a profile data file is in the native format of the host on which
 374 the profile was collected.  GNU gprof adapts automatically to the
 375 byte-order in use.
 376
 377 In the new file format, the header is followed by a sequence of
 378 records.  Currently, there are three different record types: histogram
 379 records, call-graph arc records, and basic-block execution count
 380 records.  Each file can contain any number of each record type.  When
 381 reading a file, GNU gprof will ensure records of the same type are
 382 compatible with each other and compute the union of all records.  For
 383 example, for basic-block execution counts, the union is simply the sum
 384 of all execution counts for each basic-block.
 385
 386 *** Histogram Records
 387
 388 Histogram records consist of a header that is followed by an array of
 389 bins.  The header contains the text-segment range that the histogram
 390 spans, the size of the histogram in bytes (unlike in the old BSD
 391 format, this does not include the size of the header), the rate of the
 392 profiling clock, and the physical dimension that the bin counts
 393 represent after being scaled by the profiling clock rate.  The
 394 physical dimension is specified in two parts: a long name of up to 15
 395 characters and a single character abbreviation.  For example, a
 396 histogram representing real-time would specify the long name as
 397 "seconds" and the abbreviation as "s".  This feature is useful for
 398 architectures that support performance monitor hardware (which,
 399 fortunately, is becoming increasingly common).  For example, under DEC
 400 OSF/1, the "uprofile" command can be used to produce a histogram of,
 401 say, instruction cache misses.  In this case, the dimension in the
 402 histogram header could be set to "i-cache misses" and the abbreviation
 403 could be set to "1" (because it is simply a count, not a physical
 404 dimension).  Also, the profiling rate would have to be set to 1 in
 405 this case.
 406
 407 Histogram bins are 16-bit numbers and each bin represent an equal
 408 amount of text-space.  For example, if the text-segment is one
 409 thousand bytes long and if there are ten bins in the histogram, each
 410 bin represents one hundred bytes.
 411
 412
 413 *** Call-Graph Records
 414
 415 Call-graph records have a format that is identical to the one used in
 416 the BSD-derived file format.  It consists of an arc in the call graph
 417 and a count indicating the number of times the arc was traversed
 418 during program execution.  Arcs are specified by a pair of addresses:
 419 the first must be within caller's function and the second must be
 420 within the callee's function.  When performing profiling at the
 421 function level, these addresses can point anywhere within the
 422 respective function.  However, when profiling at the line-level, it is
 423 better if the addresses are as close to the call-site/entry-point as
 424 possible.  This will ensure that the line-level call-graph is able to
 425 identify exactly which line of source code performed calls to a
 426 function.
 427
 428 *** Basic-Block Execution Count Records
 429
 430 Basic-block execution count records consist of a header followed by a
 431 sequence of address/count pairs.  The header simply specifies the
 432 length of the sequence.  In an address/count pair, the address
 433 identifies a basic-block and the count specifies the number of times
 434 that basic-block was executed.  Any address within the basic-address can
 435 be used.
 436
 437 IMPLEMENTATION NOTE: gcc -a can be used to instrument a program to
 438 record basic-block execution counts.  However, the __bb_exit_func()
 439 that is currently present in libgcc2.c does not generate a gmon.out
 440 file in a suitable format.  This should be fixed for future releases
 441 of gcc.  In the meantime, contact davidm@cs.arizona.edu for a version
 442 of __bb_exit_func() to is appropriate.