[PATCH] D62639: Fix ABI breakage with noimplicitfloat and varargs functions

[Salim Nasser via Phabricator via llvm-commits]

salim.nasser added a comment.

Note that this change will expose bug 42219 ([X86_64] Variadic functions unconditionally spill %XMM registers). In that bug report I wrote:

"Specifically this behavior may become a problem for OS kernel code compiled with -no-implicit-float when bug 36507 is fixed (https://reviews.llvm.org/D62639).

Previously, variadic functions compiled with -no-implicit-float could safely be used even with the SSE unit disabled. If we fix 36507 without fixing the present bug, such code will lead to a crash at runtime due to reading XMM registers.

I understand that it is arguable whether or not that would be a bug. For example AArch64 variadic functions always unconditionally access the vector registers. But that is because the AArch64 ABI does not provide a way to avoid this. Whereas the X86_64 ABI *does*."


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D62639/new/

https://reviews.llvm.org/D62639