[cfe-dev] Absolute paths in code coverage info

[Petr Hosek via cfe-dev]

Would there be any opposition against supporting -ffile-prefix-map in
coverage mappings in addition to -fdebug-compilation-dir? We hit this issue
recently as well, and I was thinking about implementing a similar change
for -ffile-prefix-map.

One potential issue is that -ffile-prefix-map isn't currently passed to
cc1, rather it implies --debug-prefix-map but I'm not sure if we want to
make change semantics of that flag to apply to coverage as well which would
affect existing users of -fdebug-prefix-map, maybe we should introduce a
new cc1 flag, e.g. --coverage-prefix-map, which would be also implied by
-ffile-prefix-map.

On Wed, Jun 3, 2020 at 11:09 AM Vedant Kumar via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

>
> On Jun 2, 2020, at 5:17 PM, Keith Smiley <keithbsmiley at gmail.com> wrote:
>
> FWIW after updating this patch I've verified that llvm-cov in the source
> directory with no `-path-equivalence` works fine, and also using
> `-path-equivalence=,$SRCROOT` works if you want to run it not from the
> source root.
>
>
> That’s great to hear. I’ve cc’d Reid and Yuke who may have more context on
> this patch and any potential pitfalls with it.
>
> The latter might be a bit unexpected since folks may prefer
> `-path-equivalence=.,$SRCROOT` which I'm sure we could implement if that
> was the missing piece.
>
>
> It might be sufficient to add a section to the llvm-cov command guide
> explaining how to use -fdebug-compilation-dir and -path-equivalence to get
> remote builds working.
>
> --
> Keith Smiley
>
>
> On Tue, Jun 2, 2020 at 2:49 PM Keith Smiley <keithbsmiley at gmail.com>
> wrote:
>
>> Ah actually it looks like that issue was resolved, but it was reverted a
>> second time for:
>>
>> > There seem to be bugs in llvm-cov --path-equivalence that are causing
>> Chromium problems. Revert this until they are understood or fixed.
>>
>>
>> https://github.com/llvm/llvm-project/commit/7cd595df96d5929488063d8ff5cc3b5d800386da
>>
>> Does anyone have more context on those?
>> --
>> Keith Smiley
>>
>>
>> On Tue, Jun 2, 2020 at 2:27 PM Keith Smiley <keithbsmiley at gmail.com>
>> wrote:
>>
>>> Thanks for the context! I found the revert
>>> https://github.com/llvm/llvm-project/commit/62808631acceaa8b78f8ab9b407eb6b943ff5f77 and
>>> it looks like it was caused by a small test issue. I'm a bit surprised by
>>> the justification for it since I would expect relying on the specific
>>> directory of the test to be safe, but I think I can make it work and
>>> re-submit.
>>> --
>>> Keith Smiley
>>>
>>>
>>> On Tue, Jun 2, 2020 at 10:44 AM Vedant Kumar <vsk at apple.com> wrote:
>>>
>>>> A problem that absolute paths solve in local builds is dealing with a
>>>> changing compilation directory - this can result in two different files
>>>> being referenced by the same relative path.
>>>>
>>>> There was a promising attempt to make this work with remote builds. The
>>>> idea was to have the coverage mapping logic respect a fixed compilation
>>>> directory option (https://reviews.llvm.org/D68733), i.e. the paths
>>>> embedded in the coverage mapping should be rooted at the
>>>> -fdebug-compilation-dir <path>. It looks like the patch was reverted, but
>>>> (as far as I know) there aren’t any fundamental issues with it.
>>>>
>>>> On Jun 2, 2020, at 9:57 AM, Keith Smiley via cfe-dev <
>>>> cfe-dev at lists.llvm.org> wrote:
>>>>
>>>> Hey everyone,
>>>>
>>>> Currently when generating code coverage by passing
>>>> `-fprofile-instr-generate -fcoverage-mapping` to clang, the __LLVM_COV /
>>>> __llvm_covmap section ends up containing absolute paths to the source files
>>>> being compiled. This causes issues when producing coverage info with remote
>>>> builds where the absolute paths to the source files may differ between
>>>> machines.
>>>>
>>>> llvm-cov has a `-path-equivalence` flag in order for you to remap a
>>>> single absolute path from the coverage info which definitely helps, but it
>>>> doesn't solve this entirely for the cases where you have multiple paths
>>>> that need remapping, or you're using another tool such as, Xcode's code
>>>> coverage UI, that doesn't support this kind of path remapping.
>>>>
>>>> I'm wondering if it has been discussed, or how feasible it would be,
>>>> for me to remove the necessity for absolute paths in this info.
>>>>
>>>> Thanks!
>>>> --
>>>> Keith Smiley
>>>> _______________________________________________
>>>> cfe-dev mailing list
>>>> cfe-dev at lists.llvm.org
>>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>>>
>>>>
>>>>
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