[all-commits] [llvm/llvm-project] dcc71f: [LLD][COFF] Add support for ARM64X same-address th...

[Jacek Caban via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: dcc71f22ca7f434fd15d66363770c0f53a065d7d
      https://github.com/llvm/llvm-project/commit/dcc71f22ca7f434fd15d66363770c0f53a065d7d
  Author: Jacek Caban <jacek at codeweavers.com>
  Date:   2025-07-31 (Thu, 31 Jul 2025)

  Changed paths:
    M lld/COFF/Chunks.cpp
    M lld/COFF/Chunks.h
    M lld/COFF/Config.h
    M lld/COFF/Driver.cpp
    M lld/COFF/Driver.h
    M lld/COFF/DriverUtils.cpp
    M lld/COFF/MarkLive.cpp
    M lld/COFF/Options.td
    M lld/COFF/SymbolTable.cpp
    M lld/COFF/SymbolTable.h
    M lld/COFF/Writer.cpp
    M lld/test/COFF/arm64x-sameaddress.test

  Log Message:
  -----------
  [LLD][COFF] Add support for ARM64X same-address thunks (#151255)

Fixes MSVC CRT thread-local constructors support on hybrid ARM64X
targets.

`-arm64xsameaddress` is an undocumented option that ensures the
specified function has the same address in both native and EC views of
hybrid images. To achieve this, the linker emits additional thunks and
replaces the symbols
of those functions with the thunk symbol (the same thunk is used in both
views). The thunk code jumps to the native function (similar to range
extension thunks), but additional ARM64X relocations are emitted to
replace the target with the EC function in the EC view.

MSVC appears to generate thunks even for non-hybrid ARM64EC images. As a
side effect, the native symbol is pulled in. Since this is used in the
CRT for thread-local constructors, it results in the image containing
unnecessary native code. Because these thunks do not appear to be useful
in that context, we limit this behavior to actual hybrid targets. This
may change if compatibility requires it.

The tricky part is that thunks should be skipped if the symbol is not
live in either view, and symbol replacement must be reflected in weak
aliases. This requires thunk generation to happen before resolving weak
aliases but after the GC pass. To enable this, the `markLive` call was
moved earlier, and the final weak alias resolution was postponed until
afterward. This requires more code to be aware of weak aliases, which
previously could assume they were already resolved.



To unsubscribe from these emails, change your notification settings at https://github.com/llvm/llvm-project/settings/notifications