[Vm-dev] Re: [squeak-dev] Building (Linux) VM - with segfaults. that point to audio

[Brad Fuller]

The problem might be that arrayIndex is 32bit and it is used to
calculate *samples which is 64bit. This would be a problem if
arrayIndex has bit31 set.

EXAMPLE: If arrayIndex comes in with bit31 set (e.g. 0x911f13fc),
which is negative, the top bit is extended when *samples is
calculated. samples becomes 0xffffffff911f13fc.(actual values while
debugging)

Perhaps the cast (void *)arrayIndex was to fix that.

Here's the function... I'm referencing lines 5 and 6 of the function:

====================
1 static sqInt  sound_PlaySamplesFromAtLength(sqInt frameCount, sqInt
arrayIndex, sqInt startIndex)
2 {
3  if (output_handle)
4    {
5      void *samples= (void *)arrayIndex + startIndex * output_channels * 2;
6      int   count=   snd_pcm_writei(output_handle, samples, frameCount);
7      if (count < frameCount / 2)
8	{
9	  output_buffer_frames_available= 0;
	}
      if (count < 0)
	{
	  if (count == -EPIPE)    /* underrun */
	    {
	      int err;
	      snd(pcm_prepare(output_handle), "sound_PlaySamples: snd_pcm_prepare");
	      return 0;
	    }
	  fprintf(stderr, "snd_pcm_writei returned %i\n", count);
	  return 0;
	}
      return count;
    }
  success(false);
============


Does that seem right to you all?

Maybe sqInt never gets to be long long?  sqMemoryAccess.h defines:

#if defined(SQ_IMAGE32)
 typedef int sqInt;
 typedef unsigned int usqInt;
#elif defined(SQ_HOST64)
 typedef long sqInt;
 typedef unsigned long usqInt;
#else
# if (SIZEOF_LONG_LONG != 8)
#   error long long integers are not 64-bits wide?
# endif
 typedef long long sqInt;
 typedef unsigned long long usqInt;
#endif


-- 
Brad Fuller