Better unwind table support + unwind protection in _start() and clone()
#22035
+314
−88
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The goal here is to support both levels of unwind tables (sync and async) in zig cc and zig build. Previously, the LLVM backend always used async tables while zig cc was partially influenced by whatever was Clang's default.
The function is not marked .cantunwind for Arm/Thumb because of an LLVM assembler bug: llvm/llvm-project#115891
Whatever was in the frame pointer register prior to clone() will no longer be valid in the child process, so zero it to protect FP-based unwinders. Similarly, mark the link register as undefined to protect DWARF-based unwinders. This is only zeroing the frame pointer(s) on Arm/Thumb because of an LLVM assembler bug: llvm/llvm-project#115891
Whatever was in the frame pointer register prior to clone() will no longer be valid in the child process, so zero it to protect FP-based unwinders. This is just an extension of what was already done for i386 and x86_64. Only applied to architectures where the _start() code also zeroes the frame pointer.
alexrp
commented
Nov 20, 2024
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