[PATCH] D143803: [clang][alias|ifunc]: Add a diagnostic for mangled names

[David Blaikie via Phabricator via cfe-commits]

dblaikie added a comment.

In D143803#4120000 <https://reviews.llvm.org/D143803#4120000>, @0xdc03 wrote:

> Note that as it stands currently, this patch cannot be committed because the test `clang/test/SemaCXX/externc-ifunc-resolver.cpp` fails to run. The contents of the test are as follows:
>
>   // RUN: %clang_cc1 -emit-llvm-only -triple x86_64-linux-gnu -verify %s
>   
>   extern "C" {
>   __attribute__((used)) static void *resolve_foo() { return 0; }
>   namespace NS {
>   __attribute__((used)) static void *resolve_foo() { return 0; }
>   } // namespace NS
>   
>   // FIXME: This diagnostic is pretty confusing, the issue is that the existence
>   // of the two functions suppresses the 'alias' creation, and thus the ifunc
>   // resolution via the alias as well. In the future we should probably find
>   // some way to improve this diagnostic (likely by diagnosing when we decide
>   // this case suppresses alias creation).
>   __attribute__((ifunc("resolve_foo"))) void foo(); // expected-error{{ifunc must point to a defined function}}
>   }
>
> The error that I get is as follows:
>
>   Command Output (stderr):
>   --
>   + : 'RUN: at line 1'
>   + /mnt/entschuldigung/LLVM/llvm-main/build-release/bin/clang -cc1 -internal-isystem /mnt/entschuldigung/LLVM/llvm-main/build-release/lib/clang/17/include -nostdsysteminc -emit-llvm-only -triple x86_64-linux-gnu -verify /mnt/entschuldigung/LLVM/llvm-main/clang/test/SemaCXX/externc-ifunc-resolver.cpp
>   error: 'note' diagnostics seen but not expected:
>     File /mnt/entschuldigung/LLVM/llvm-main/clang/test/SemaCXX/externc-ifunc-resolver.cpp Line 14: 'resolve_foo' exists as a mangled name, did you mean to use '_ZL11resolve_foov'?
>     File /mnt/entschuldigung/LLVM/llvm-main/clang/test/SemaCXX/externc-ifunc-resolver.cpp Line 14: 'resolve_foo' exists as a mangled name, did you mean to use '_ZN2NSL11resolve_fooEv'?
>   2 errors generated.
>   
>   --
>
> which confuses me because an `extern "C"` block is not supposed to mangle any names, right? Appreciate any inputs on this.

Looks like maybe a Clang feature, that since they're "static"/internal linkage, Clang decides it can still mangle them: https://godbolt.org/z/6oMfjced1 - GCC doesn't do this, and fails if you try to overload them, whereas clang doesn't.

That does surprise me - if only for GCC/Clang compatibility, regardless of what the spec says, exactly...


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