RFC: AutoFDO GCOV Profile Format Version 4

[Dhruv Chawla]

On 28/04/26 23:23, Jose E. Marchesi wrote:
> External email: Use caution opening links or attachments
> 
> 
>> On 23/04/26 14:27, Jose E. Marchesi wrote:
>>> External email: Use caution opening links or attachments
>>>
>>>> Hi all,
>>>>
>>>> Per prior discussions, here is the specification we are proposing for
>>>> version 4 of the AutoFDO GCOV profile format. This is a complete re-design
>>>> focused around being a backwards-compatible and extensible format which
>>>> can be partially read by the compiler.
>>> Could you please send me (off list) a sample data file, as complete
>>> as
>>> possible?  Thanks!
>>
>> Hi Jose,
>>
>> Just curious as to why you need an example? No problems with sharing it,
>> is there any particular part of the design you are interested in taking a
>> look at? Meaningful profiles are rather unwieldy due to their size.
> 
> I intend to review the proposed format by writing a GNU poke pickle for
> it, as complete as possible, including constraints etc.  On one hand, it
> is a good way to catch potential pitfalls in the designed encoding, data
> integrity, etc.  On the other, you get an easy to update pickle for
> free, to poke at data, dump to the textual representation, construct
> test cases, and the like.
> 
> Having a sample binary will help.  It doesn't have to contain large sets
> of data, but the more of the spec it exercises, the better.
> 
> For reference, you cand find a pickle for gcov streams at
> https://cgit.git.savannah.gnu.org/cgit/poke.git/tree/pickles/gcov.pk

Hi Jose,

Apologies for the late reply. I've attached some files to this
mail that try to exhibit most of the features in the format:

- example.c: Simple testcase
- example.gcov: GCOV v3 profile
- example.gcov.v4: GCOV v4 profile
- example.gcov.v4.compact: GCOV v4 compact profile

The testcase was compiled with -O2 -g -fno-omit-frame-pointer.

-- 
Regards,
Dhruv
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__attribute__ ((noinline, noipa)) static void foo_1 () {}
__attribute__ ((noinline, noipa)) static void foo_2 () {}

static void (*foos[]) () = { foo_1, foo_2 };

__attribute__ ((noinline, noipa)) static void bar_1 () { foo_1 (); foo_2 (); }
__attribute__ ((noinline, noipa)) static void bar_2 (int i) { foos[i & 1](); }

inline static void bar_3 (int i) { if (i & 1) foo_1 (); else foo_2 (); }

int
main ()
{
  for (int i = 0; i < 1000000; i++)
    {
      bar_1 ();
      bar_2 (i);
      bar_3 (i);
    }
}
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