[cfe-dev] Absolute paths in code coverage info

[Max Moroz via cfe-dev]

No objections from me!

On Thu, Jun 25, 2020 at 11:42 AM Vedant Kumar <vsk at apple.com> wrote:

> Thanks Keith, that sounds great to me!
>
> vedant
>
> On Jun 24, 2020, at 6:11 PM, Keith Smiley <keithbsmiley at gmail.com> wrote:
>
> Yes. I'm happy to implement the plan as I it understand so far. Please
> correct me if I'm wrong.
>
> 1. Add the new -coverage-prefix-map flag
> 2. Make -ffile-prefix-map imply this new flag.
> 3. No new *dir flags for now
> 4. No changes to -fdebug-prefix-map
>
> --
> Keith Smiley
>
>
> On Wed, Jun 24, 2020 at 4:10 PM Max Moroz <mmoroz at chromium.org> wrote:
>
>> Sorry for the late reply (I was on leave). Is this still relevant?
>>
>> On Tue, Jun 9, 2020 at 5:50 PM Vedant Kumar <vsk at apple.com> wrote:
>>
>>> Any objections to starting with having -ffile-prefix-map imply “relative
>>> paths for coverage mappings”? I think this would work for both Petr and
>>> Keith’s use cases.
>>>
>>> vedant
>>>
>>> On Jun 5, 2020, at 11:04 AM, Vedant Kumar <vsk at apple.com> wrote:
>>>
>>>
>>> On Jun 4, 2020, at 4:17 PM, Dan McGregor <danismostlikely at gmail.com>
>>> wrote:
>>>
>>> I like Vendant and Petr's proposals. -ffile-prefix-map was really
>>> intended to be a union of -fdebug-prefix-map and -fmacro-prefix-map.
>>> If a coverage-prefix-map is added I think it makes sense to add it to
>>> file-prefix-map.
>>>
>>>
>>> Thanks Dan. This part sounds good to me. If I’ve understood the
>>> motivation for https://reviews.llvm.org/D68733, and given Petr’s plans,
>>> it sounds there’s interest in both the coverage-prefix-map and the
>>> coverage-compilation-dir options. Is that a fair summary?
>>>
>>> Likewise for debug-compilation-dir and
>>> coverage-compilation-dir, and any hypothetical users of
>>> macro-compilation-dir, though I don't think the compilation directory
>>> is exposed to the preprocessor at all..
>>>
>>>
>>> Is your preference for -coverage-compilation-dir being set by
>>> -file-prefix-map, or for a new union flag that sets a relative compilation
>>> dir (like -ffile-compilation-dir)? I’m assuming the latter, since the
>>> summary from https://reviews.llvm.org/D63387 states that a downside of
>>> the -fdebug-prefix-map=old=new syntax is that it "requires putting the
>>> absolute path to the build directory on the build command line”, which I
>>> suppose we’d want to avoid for any *-compilation-dir flag. I’d be
>>> interested in hearing what others think as well.
>>>
>>> vedant
>>>
>>>
>>> On Thu, 4 Jun 2020 at 15:08, Keith Smiley <keithbsmiley at gmail.com>
>>> wrote:
>>>
>>>
>>> I don't have a ton of context on the history of all these flags, but I'm
>>> happy to implement either of those solutions once we have consensus!
>>> --
>>> Keith Smiley
>>>
>>>
>>> On Thu, Jun 4, 2020 at 12:05 PM Vedant Kumar <vsk at apple.com> wrote:
>>>
>>>
>>>
>>> On Jun 3, 2020, at 2:38 PM, Petr Hosek <phosek at chromium.org> wrote:
>>>
>>> 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.
>>>
>>>
>>> I think it’s a good idea.
>>>
>>> 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,
>>>
>>>
>>> Thanks for flagging this. You’re right, changing the absolute path
>>> behavior under -fdebug-prefix-map might break llvm-cov workflows which
>>> aren’t using -path-equivalence. -ffile-prefix-map seems relatively new, and
>>> also its purpose is to be a ‘union’ of other *prefix-map options, so having
>>> this imply —coverage-prefix-map makes sense to me.
>>>
>>> maybe we should introduce a new cc1 flag, e.g. --coverage-prefix-map,
>>> which would be also implied by -ffile-prefix-map.
>>>
>>>
>>> Sounds good to me. But for consistency, maybe we should rethink how
>>> -fdebug-compilation-dir <relpath> is handled. A couple options:
>>>
>>> - Have `-fdebug-compilation-dir <relpath>` (driver flag) imply
>>> `—coverage-prefix-map=$(abspath <relpath>)=./` (cc1 flag).
>>>
>>> The absolute path is hidden from the driver invocation, so this can
>>> still be used by a caching build system. I’m assuming we don’t embed the
>>> cc1 flags anywhere, e.g. not in the DW_AT_APPLE_flags. This is the closest
>>> to what https://reviews.llvm.org/D81122 is currently doing.
>>>
>>> - Introduce `-ffile-compilation-dir <relpath>` (driver flag), which
>>> implies `-fdebug-compilation-dir <relpath>` (cc1 flag) and a new
>>> `-fcoverage-compilation-dir <relpath>`
>>>
>>> Essentially, make -ffile-compilation-dir analogous to -ffile-prefix-map,
>>> a union of *compilation-dir options.
>>>
>>> vedant
>>>
>>>
>>> On Wed, Jun 3, 2020 at 11:09 AM Vedant Kumar via cfe-dev <
>>> cfe-dev at lists.llvm.org> wrote:
>>>
>>>
>>>
>>> On Jun 2, 2020, at 5:17 PM, Keith Smiley <keithbsmiley at gmail.com> wrote:
>>>
>>> FWIW after updating this patch I've verified that llvm-cov in the source
>>> directory with no `-path-equivalence` works fine, and also using
>>> `-path-equivalence=,$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
>>> _______________________________________________
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>>> cfe-dev at lists.llvm.org
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>>>
>>>
>>>
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>>>
>>>
>>>
>>>
>>> --
> --
> Keith Smiley
>
>
>
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