[PATCH] D135189: [lld/mac] With -demangle, strip leading _ from non-mangled names

[Nico Weber via Phabricator via llvm-commits]

thakis created this revision.
thakis added a reviewer: lld-macho.
Herald added projects: lld-macho, All.
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For

  void f();
  int main() { f(); }

`lld -demangle` now produces

  ld64.lld: error: undefined symbol: f
  >>> referenced by path/to/main.o:(symbol main+0x8)

instead of

  ld64.lld: error: undefined symbol: _f
  >>> referenced by path/to/main.o:(symbol _main+0x8)

previously. (Without `-demangle`, it still prints `_f` and `_main`.)

This does *not* match ld64's behavior, but it does match e.g. lld/COFF's
behaviour.

This is arguably easier to understand: clang prepends symbol names with `_`
on macOS, so it seems friendly if the linker removes it again in its
diagnostics. It also makes the `extern "C"` insertion diagnostics we added
recently look more self-consistent.

--------------------

I'm not 100% sure this is a good idea, but it might be. Maybe best to land
it for a while and see how it feels?


https://reviews.llvm.org/D135189

Files:
  lld/MachO/Symbols.cpp
  lld/test/MachO/invalid/duplicate-symbol.s
  lld/test/MachO/invalid/undefined-symbol.s
  lld/test/MachO/undef-suggest-extern-c.s
  lld/test/MachO/undef-suggest-extern-c2.s

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