[cfe-dev] compiler-rt RFE to support creating profraw for each Shared Library

[Oza, Hiral via cfe-dev]

Hello Vedant,

> What's not clear to me is why dso-specific .profraw files are helpful for code coverage, since merged .profraw's should work just as well.
> Have you encountered issues using merged .profraws? Could you clarify what's meant by backtracking and instrumenting [the] final binary?

There were problems when decoding merged profraw files. Couldn’t recall exactly error messages. But symbols in the profraws could not at all be matched to their definitions in the .so files.
Also tried %m which worked, except that we had no way to know which .so file corresponded to which .profraw file when decoding them.
Hence we added %n.

Thank you.
-Hiral


From: Vedant Kumar <vsk at apple.com>
Sent: Friday, 24 September, 2021 00:01
To: Oza, Hiral <Hiral.Oza at netapp.com>
Cc: llvm-dev at lists.llvm.org; cfe-dev at lists.llvm.org
Subject: Re: [cfe-dev] compiler-rt RFE to support creating profraw for each Shared Library

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Hi Oza,

The mechanics of the patch are clear. What's not clear to me is why dso-specific .profraw files are helpful for code coverage, since merged .profraw's should work just as well.

Have you encountered issues using merged .profraws? Could you clarify what's meant by backtracking and instrumenting [the] final binary?

thanks,
vedant


On Sep 22, 2021, at 9:36 PM, Oza, Hiral <Hiral.Oza at netapp.com<mailto:Hiral.Oza at netapp.com>> wrote:

Hello Vedant,

> could you share some of the use cases for this feature? > What were the pros/cons of any alternatives you considered (e.g. the %m/%c modes)?

We are taking coverage of shared libraries (i.e. Linux .so) and dumping coverage into files corresponding to SO’s filename.
With this proposed patch, will get coverage as below for sample code (pls refer compiler-rt/test/profile/Linux/instrprof-shared-nProfraws.test):
libhi.so  -> will dump into libhi.so.profraw
libhello.so -> will dump into libhellp.so.profraw
main.out -> will dump into main.out.profraw

Regarding ‘%m or %c: (from https://clang.llvm.org/docs/SourceBasedCodeCoverage.html): %m is expands instrumented binary’s signature (and with “%Nm” dumps into poll of N profraws) and %c seems very different from proposed “%n”.

Basically with proposed patch (i.e. using “%n”) one can get one-to-one mapping of Shared Library and generated .profraw.
This makes backtracking and instrumenting final-binary based on feedback easy.

Please let me know in case of further queries or any changes in proposed patch.

Thank you.
-Hiral

From: cfe-dev <cfe-dev-bounces at lists.llvm.org<mailto:cfe-dev-bounces at lists.llvm.org>> On Behalf Of Oza, Hiral via cfe-dev
Sent: Wednesday, 22 September, 2021 18:56
To: cfe-dev at lists.llvm.org<mailto:cfe-dev at lists.llvm.org>; llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>>
Subject: [cfe-dev] compiler-rt RFE to support creating profraw for each Shared Library

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Greetings!

Please review our patch compiler-rt RFE patch here -- https://reviews.llvm.org/D110232

This patch is about creating profraw for each Shared Library.

<patch_info>

SBCC RFE: Support SBCC for Shared Library



SBCC RFE: Support SBCC for Shared Library

Using '%n' format parameter for profile name templates, to insert the full

path of the current shared object into profile file names.



Internally using a linked list to gather all profile dumping functions

(there is one defined in each shared object) so they can be invoked with a

single function call.  Ensure the resulting directory paths are created

prior to dumping.
</patch_info>

Thank you in advance for your kind review.
-Hiral

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