[cfe-dev] Absolute paths in code coverage info

Wed Jun 24 16:09:21 PDT 2020

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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