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Valgrind 3.3 - Advanced Debugging and Profiling for GNU/Linux applications
by J. Seward, N. Nethercote, J. Weidendorfer and the Valgrind Development Team
Paperback (6"x9"), 164 pages
ISBN 0954612051
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6.2.3 Annotating C/C++ programs

Before using cg_annotate, it is worth widening your window to be at least 120-characters wide if possible, as the output lines can be quite long.

To get a function-by-function summary, run ‘cg_annotate <filename>’ on a Cachegrind output file.

The output looks like this:

-------------------------------------------------------
I1 cache:              65536 B, 64 B, 2-way associative
D1 cache:              65536 B, 64 B, 2-way associative
L2 cache:              262144 B, 64 B, 8-way associative
Command:               concord vg_to_ucode.c
Events recorded:  Ir I1mr I2mr Dr D1mr D2mr Dw D1mw D2mw
Events shown:     Ir I1mr I2mr Dr D1mr D2mr Dw D1mw D2mw
Event sort order: Ir I1mr I2mr Dr D1mr D2mr Dw D1mw D2mw
Threshold:             99%
Chosen for annotation:
Auto-annotation:       on

-------------------------------------------------------
Ir         I1mr I2mr Dr         D1mr   D2mr  Dw        
  D1mw   D2mw
-------------------------------------------------------
27,742,716  276  275 10,955,517 21,905 3,987 4,474,773 
  19,280 19,098  PROGRAM TOTALS

-------------------------------------------------------
Ir        I1mr I2mr Dr        D1mr  D2mr  Dw        
  D1mw   D2mw    file:function
-------------------------------------------------------
8,821,482    5    5 2,242,702 1,621    73 1,794,230 
       0      0  getc.c:_IO_getc
5,222,023    4    4 2,276,334    16    12   875,959 
       1      1  concord.c:get_word
2,649,248    2    2 1,344,810 7,326 1,385         . 
       .      .  vg_main.c:strcmp
2,521,927    2    2   591,215     0     0   179,398 
       0      0  concord.c:hash
2,242,740    2    2 1,046,612   568    22   448,548 
       0      0  ctype.c:tolower
1,496,937    4    4   630,874 9,000 1,400   279,388 
       0      0  concord.c:insert
  897,991   51   51   897,831    95    30        62 
       1      1  ???:???
  598,068    1    1   299,034     0     0   149,517 
       0      0  lockfile.c:__flockfile
  598,068    0    0   299,034     0     0   149,517 
       0      0  lockfile.c:__funlockfile
  598,024    4    4   213,580    35    16   149,506 
       0      0  vg_clientmalloc.c:malloc
  446,587    1    1   215,973 2,167   430   129,948 
  14,057 13,957  concord.c:add_existing
  341,760    2    2   128,160     0     0   128,160 
       0      0  vg_clientmalloc.c:vg_trap_here_WRAPPER
  320,782    4    4   150,711   276     0    56,027 
      53     53  concord.c:init_hash_table
  298,998    1    1   106,785     0     0    64,071 
       1      1  concord.c:create
  149,518    0    0   149,516     0     0         1 
       0      0  ???:tolower@@GLIBC_2.0
  149,518    0    0   149,516     0     0         1 
       0      0  ???:fgetc@@GLIBC_2.0
   95,983    4    4    38,031     0     0    34,409 
   3,152  3,150  concord.c:new_word_node
   85,440    0    0    42,720     0     0    21,360 
       0      0  vg_clientmalloc.c:vg_bogus_epilogue

First up is a summary of the annotation options:

Then follows summary statistics for the whole program. These are similar to the summary provided when running ‘valgrind --tool=cachegrind’.

Then follows function-by-function statistics. Each function is identified by a ‘file_name:function_name’ pair. If a column contains only a dot it means the function never performs that event (e.g. the third row shows that ‘strcmp()’ contains no instructions that write to memory). The name ‘???’ is used if the the file name and/or function name could not be determined from debugging information. If most of the entries have the form ‘???:???’ the program probably wasn't compiled with ‘-g’. If any code was invalidated (either due to self-modifying code or unloading of shared objects) its counts are aggregated into a single cost centre written as ‘(discarded):(discarded)’.

It is worth noting that functions will come both from the profiled program (e.g. ‘concord.c’) and from libraries (e.g. ‘getc.c’)

There are two ways to annotate source files--by choosing them manually, or with the ‘--auto=yes’ option. To do it manually, just specify the filenames as additional arguments to cg_annotate. For example, the output from running ‘cg_annotate <filename> concord.c’ for our example produces the same output as above followed by an annotated version of ‘concord.c’, a section of which looks like:

-------------------------------------------------------
-- User-annotated source: concord.c
-------------------------------------------------------
Ir        I1mr I2mr Dr      D1mr  D2mr  Dw  D1mw   D2mw

    .    .    .       .     .     .    .      .      .
void init_hash_table(char *file_name, Word_Node *table[])
    3    1    1       .     .     .    1      0      0
  {
    .    .    .       .     .     .    .      .      .
      FILE *file_ptr;
    .    .    .       .     .     .    .      .      .
      Word_Info *data;
    1    0    0       .     .     .    1      1      1
      int line = 1, i;
    .    .    .       .     .     .    .      .      .
    5    0    0       .     .     .    3      0      0
      data = (Word_Info *) create(sizeof(Word_Info));
    .    .    .       .     .     .    .      .      .
4,991    0    0   1,995     0     0   998      0      0
      for (i = 0; i < TABLE_SIZE; i++)
3,988    1    1   1,994     0     0   997     53     52
          table[i] = NULL;
    .    .    .       .     .     .    .      .      .
    .    .    .       .     .     .    .      .      .
      /* Open file, check it. */
    6    0    0       1     0     0    4      0      0
      file_ptr = fopen(file_name, "r");
    2    0    0       1     0     0    .      .      .
      if (!(file_ptr)) {
    .    .    .       .     .     .    .      .      .
          fprintf(stderr, "Couldn't open '%s'.\n", 
                         file_name);
    1    1    1       .     .     .    .      .      .
          exit(EXIT_FAILURE);
    .    .    .       .     .     .    .      .      .
      }
    .    .    .       .     .     .    .      .      .
165,062  1    1  73,360     0     0  91,700   0      0
  while ((line = get_word(data, line, file_ptr)) != EOF)
146,712  0    0  73,356     0     0  73,356   0      0
          insert(data->;word, data->line, table);
    .    .    .       .     .     .    .      .      .
    4    0    0       1     0     0    2      0      0
      free(data);
    4    0    0       1     0     0    2      0      0
      fclose(file_ptr);
    3    0    0       2     0     0    .      .      .
  }

(Although column widths are automatically minimised, a wide terminal is clearly useful.)

Each source file is clearly marked (‘User-annotated source’) as having been chosen manually for annotation. If the file was found in one of the directories specified with the ‘-I / --include’ option, the directory and file are both given.

Each line is annotated with its event counts. Events not applicable for a line are represented by a dot. This is useful for distinguishing between an event which cannot happen, and one which can but did not.

Sometimes only a small section of a source file is executed. To minimise uninteresting output, Cachegrind only shows annotated lines and lines within a small distance of annotated lines. Gaps are marked with the line numbers so you know which part of a file the shown code comes from, e.g.:

(figures and code for line 704)
-- line 704 ----------------------------------------
-- line 878 ----------------------------------------
(figures and code for line 878)

The amount of context to show around annotated lines is controlled by the ‘--context’ option.

To get automatic annotation, run ‘cg_annotate <filename> --auto=yes’. cg_annotate will automatically annotate every source file it can find that is mentioned in the function-by-function summary. Therefore, the files chosen for auto-annotation are affected by the ‘--sort’ and ‘--threshold’ options. Each source file is clearly marked (‘Auto-annotated source’) as being chosen automatically. Any files that could not be found are mentioned at the end of the output, e.g.:

-------------------------------------------------------
The following files chosen for auto-annotation could 
not be found:
-------------------------------------------------------
  getc.c
  ctype.c
  ../sysdeps/generic/lockfile.c

This is quite common for library files, since libraries are usually compiled with debugging information, but the source files are often not present on a system. If a file is chosen for annotation both manually and automatically, it is marked as ‘User-annotated source’. Use the ‘-I / --include’ option to tell Valgrind where to look for source files if the filenames found from the debugging information aren't specific enough.

Beware that cg_annotate can take some time to digest large ‘cachegrind.out.<pid>’ files, e.g. 30 seconds or more. Also beware that auto-annotation can produce a lot of output if your program is large!

ISBN 0954612051Valgrind 3.3 - Advanced Debugging and Profiling for GNU/Linux applicationsSee the print edition