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问题:

I receive some error when evaluating my program using valgrind. More precisely, I get errors like

vex amd64->IR: unhandled instruction bytes: 0xC5 0xF8 0x28 0x0 0xC5 0xF8 0x29 0x45 ... ... Illegal instruction

I isolated the problem to a very simple example

#include <immintrin.h>
int main() {
  float f __attribute__((aligned(16))); // No need to be aligned
  f = 2.0f;
  __m128 a = _mm_broadcast_ss(&f);
  return 0;
}

The program is compiled using gcc with the options -mavx. If the SSE2 instruction _mm_set1_ps is used instead, the same error occurs but only when compiled with -mavx. When compiling the program using -msse2, valgrind reports no errors.

I suspect this is a valgrind bug, but can't find any reports on this for x86. My machine is a Core-i7 Sandy-Bridge and valgrind version 3.7.0.

If anyone have a better alternative to valgrind for register-aware programming, I would like to know.

Thanks in advance

回答1:

mm_broadcast_ss translates to a single CPU instruction and it requires the AVX instruction set. You may need a more up-to-date valgrind to support that instruction, at least release 3.8.0 (10 August 2012).

See the Valgrind core documentation for an explanation.