russell.gallop added a subscriber: ruiu.
russell.gallop added a comment.
> Hello, this embeds an absolute path into the generated .obj file, which means
> the output now is no longer deterministic (since it depends on the absolute
> path to clang_rt.profile-x86_64.lib).
Yes, it embeds the absolute path. Note that -fsanitize=undefined has done that
since r241225 (in 2015).
> This means the output will be different on different machines, which breaks
> things like caching in distributed builds and whatnot.
I assume that your distributed build sandboxes tool paths so this is
deterministic from one users point of view, just not deterministic across users
with tools installed in different locations so it defeats the cache. Yes,
that's not ideal.
> I can't see an obvious way to save this patch either, since you won't know at
> compile time what the CWD will be at link time.
I assume you're considering relative paths here. Yes, I don't think that would
work nicely.
> As-is, this breaks Chromium's deterministic builds. ("Only" the coverage
> builds, and they don't yet check for determinism, which is why it took us a
> while to notice.)
> Suggestions?
If this was made into a library name instead of a path (e.g.
--dependent-lib=clang_rt.profile-x86_64.lib) then it would solve the problem of
different paths on different nodes, but then you would have to tell the linker
where to find this library.
That is *almost* as bad as having to specify the full path to the library to
the linker in the first place! It's not quite as bad as you don't have to
specify the architecture and you only need to specify it once regardless of
whether you're using profiling or sanitizers. If lld-link added the clang
library path itself, then the library name would be all that was needed from
the compiler side.
Rui, would it be possible for lld-link to search the path to the clang
libraries (e.g. C:\Program Files\LLVM\lib\clang\8.0.0\lib\windows) by default?
Would this have any undesirable side effects?
Repository:
rC Clang
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D61742/new/
https://reviews.llvm.org/D61742
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