[PATCH] D104556: [InstrProfiling] Make CountersPtr in __profd_ relative

[Reid Kleckner via Phabricator via cfe-commits]

rnk added a comment.

In D104556#2831787 <https://reviews.llvm.org/D104556#2831787>, @MaskRay wrote:

> Hmm, IMGREL (`IMAGE_REL_AMD64_ADDR32NB`) looks useful and is an alternative solution to PC-relative relocations in ELF / relocation subtraction in Mach-O.
> But leveraging it seems to need more code in the runtime and will make COFF vs non-COFF different in IR, runtime, and llvm-profdata....

We can go forward with what we have, but the `signextIfWin64` helper is pretty subtle. In some ways, I think adding `__ImageBase` is clearer:

  #ifdef _WIN32
  extern "C" char __ImageBase;
  #endif
  uintptr_t rebaseRelativePtr(void *D, void *P) {
  #ifdef _WIN32
    return (uintptr_t)&__ImageBase + (uintptr_t)P;
  #else
    return (uintptr_t)D + (uintptr_t)P;
  #endif
  }

It's not quite this easy, and the instrumentation side changes have to basically copy or refactor this code:
https://github.com/llvm/llvm-project/blob/main/clang/lib/CodeGen/MicrosoftCXXABI.cpp#L548

We aren't worried about profraw format compatibility on Windows, so I think we can change this later at any time if we like.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D104556/new/

https://reviews.llvm.org/D104556