[cfe-dev] Absolute paths in code coverage info

Wed Jun 24 18:11:50 PDT 2020

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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>>
>>
>>
>> --
--
Keith Smiley
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