[PATCH] D145650: [X86] Create extra prolog/epilog for stack realignment

Fri Mar 24 12:41:29 PDT 2023

rupprecht added a comment.

This relanded in e4ceb5a7bb9b8f6d730530345649286370dd3ff8 <https://reviews.llvm.org/rGe4ceb5a7bb9b8f6d730530345649286370dd3ff8>, and we're seeing runtime errors in Halide when building with asan.

I don't have a standalone reproducer I can share yet, but the issue we see is when attempting to return from this method: https://github.com/halide/Halide/blob/main/src/runtime/x86_cpu_features.cpp. If I had to guess, it's a bad interaction with the cpuid implementation here: https://github.com/halide/Halide/blob/2a51f71a0add536ab986c675d1239db860dbc655/src/runtime/x86.ll#L145

The problem is `$rsp` is not pointing to the right place, and so `ret` jumps to a bogus location, so the next instruction faults:

  ... break on start address of x86_cpu_features ...
  (lldb) x/2 $rsp
  0x7fffffffb818: 0x5806dc35 0x00005555
  (lldb) c
  ...
  (lldb) di -l

  repro_test`Halide::Runtime::Internal::halide_get_cpu_features:
      0x55555806e23e <+1246>: movq   -0x48(%rbp), %r10
      0x55555806e242 <+1250>: leaq   -0x28(%rbp), %rsp
      0x55555806e246 <+1254>: popq   %rbx
      0x55555806e247 <+1255>: popq   %r12
      0x55555806e249 <+1257>: popq   %r13
      0x55555806e24b <+1259>: popq   %r14
      0x55555806e24d <+1261>: popq   %r15
      0x55555806e24f <+1263>: popq   %rbp
      0x55555806e250 <+1264>: leaq   -0x10(%r10), %rsp
  ->  0x55555806e254 <+1268>: retq
  (lldb) x/2 $rsp
  0x7fffffffb810: 0xffffb890 0x00007fff
  (lldb) x/2 0x7fffffffb818
  0x7fffffffb818: 0x5806dc35 0x00005555

Repository:
  rG LLVM Github Monorepo

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https://reviews.llvm.org/D145650