[PATCH] D104978: [lld/mac] Don't fold UNWIND_X86_64_MODE_STACK_IND unwind entries

[Nico Weber via Phabricator via llvm-commits]

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libunwind uses unwind info to find the function address belonging
to the current instruction pointer. libunwind/src/CompactUnwinder.hpp's
step functions read functionStart for UNWIND_X86_64_MODE_STACK_IND
(and for nothing else), so these encodings need a dedicated entry
per function, so that the runtime can get the stacksize off the
`subq` instrunction in the function's prologue.

This matches ld64.

(CompactUnwinder.hpp from https://opensource.apple.com/source/libunwind/
also reads functionStart in a few more cases if `SUPPORT_OLD_BINARIES` is set,
but it defaults to 0, and ld64 seems to not worry about these additional
cases.)

Related upstream bug: https://crbug.com/1220175


https://reviews.llvm.org/D104978

Files:
  lld/MachO/UnwindInfoSection.cpp
  lld/test/MachO/compact-unwind-stack-ind.s

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