[PATCH] D154125: MachineFunction: -fsanitize={function, kcfi}: ensure 4-byte alignment

[Fangrui Song via Phabricator via llvm-commits]

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Fix https://github.com/llvm/llvm-project/issues/63579

  % cat a.c
  void foo() {}
  % clang --target=arm-none-eabi -mthumb -mno-unaligned-access -fsanitize=kcfi a.c -S -o - | grep p2align
          .p2align        1
  % clang --target=armv6m-none-eabi -fsanitize=function a.c -S -o - | grep p2align
          .p2align        1

Ensure that -fsanitize={function,kcfi} instrumented functions are aligned by at
least 4, so that loading the type hash before the function label will not cause
a misaligned access. This is especially important for -mno-unaligned-access
configurations that doesn't set `setMinFunctionAlignment` to 4 or greater.

With this patch, the generated assembly for the examples above will contain `.p2align 2`.

If `__attribute__((aligned(N)))` or `-falign-functions=N` is specified, the
larger alignment will be used.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D154125

Files:
  llvm/lib/CodeGen/MachineFunction.cpp
  llvm/test/CodeGen/ARM/func-sanitizer.ll
  llvm/test/CodeGen/ARM/kcfi.ll
  llvm/test/CodeGen/RISCV/kcfi-patchable-function-prefix.ll

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