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

[Vedant Kumar via llvm-dev]

> On Sep 28, 2021, at 12:08 AM, Oza, Hiral <Hiral.Oza at netapp.com> wrote:
> 
> 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.

I think it'd be instructive to dig into these problems a bit more. How were .profraw contents matched to symbols in a .so? Can you share a minimal test case with (say) two .so's that illustrates the issue with merged .profraws?

To add some context for the line of inquiry: llvm's infrastructure has supported collecting profile data from processes with multiple instrumented DSOs for quite a while. If the existing flow to emit & use merged .profraws for coverage reporting has stopped working, or is buggy, that would indicate a serious regression which we should fix.

> Also tried %m which worked, except that we had no way to know which .so file corresponded to which .profraw file when decoding them.

Why is it necessary to know the precise mapping of .profraw files to DSOs? Typically, .profraw files are merged together into an indexed .profdata (via `llvm-profdata merge ...`): that in turn supports coverage analysis for all of the DSOs that contributed profile data.

> Hence we added %n.

I'd be hesitant towards adding this to the profile runtime as a workaround for a deeper issue.

thanks,
vedant

>  
> Thank you.
> -Hiral
>  
>  
> From: Vedant Kumar <vsk at apple.com <mailto:vsk at apple.com>> 
> Sent: Friday, 24 September, 2021 00:01
> To: Oza, Hiral <Hiral.Oza at netapp.com <mailto:Hiral.Oza at netapp.com>>
> Cc: llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>; cfe-dev at lists.llvm.org <mailto:cfe-dev at lists.llvm.org>
> Subject: Re: [cfe-dev] compiler-rt RFE to support creating profraw for each Shared Library
>  
> NetApp Security WARNING: This is an external email. Do not click links or open attachments unless you recognize the sender and know the content is safe. 
> 
> 
> 
> 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 <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
>  
> NetApp Security WARNING: This is an external email. Do not click links or open attachments unless you recognize the sender and know the content is safe.
> 
> 
> 
> 
> Greetings!
>  
> Please review our patch compiler-rt RFE patch here -- https://reviews.llvm.org/D110232 <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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