[gstreamer-bugs] [Bug 606198] New: rtph264pay is causing alignment trap on ARM arch

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=606198
  GStreamer | gst-plugins-good | 0.10.16

           Summary: rtph264pay is causing alignment trap on ARM arch
    Classification: Desktop
           Product: GStreamer
           Version: 0.10.16
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: gst-plugins-good
        AssignedTo: gstreamer-bugs at lists.sourceforge.net
        ReportedBy: brijesh.ksingh at gmail.com
         QAContact: gstreamer-bugs at lists.sourceforge.net
      GNOME target: ---
     GNOME version: ---


Hello,

I'm working on TI ARM processor and have likely found an issue with rtph264pay
payload element. On some cases I get bus error as shown below: 

"Alignment trap: gst-launch-0.10 (803) PC=0x40dde948 Instr=0xe5933000
Address=0x000b9011 FSR 0x013"

This indicated that rtph264pay is trying to access an unaligned memory. And by
default kernel generates Bus error on unaligned memory access.  

Looking at the code indicates that this unaligned access is coming from
"is_nal_equal()" routine.  

<snip>
/* we don't use memcpy but this faster version (around 20%) because we need to
 * perform it on all data. */
static gboolean
is_nal_equal (const guint8 * nal1, const guint8 * nal2, guint len)
{
 /* if we have a 64-bit processor, we may use guint64 to make 
   * this go faster. Otherwise with 32 bits, we are already
   * going faster than byte to byte compare.
   */
  guint remainder = len & 0x3;
  guint num_int = len >> 2;
  guint32 *pu1 = (guint32 *) nal1, *pu2 = (guint32 *) nal2;
  guint i;

  /* compare by groups of sizeof(guint32) bytes */
  for (i = 0; i < num_int; i++) {
    /* XOR is faster than CMP?... */
    if (pu1[i] ^ pu2[i])
      return FALSE;
  }
..........
<snip>
}

Lets consider the case when len=9. If len=9 then memory is not 32-bit aligned
and will cause trap while comparing (pu1[1] ^ pu2[1]).

If i force kernel to "fixup" alignment problem (i.e echo 2 >
/proc/cpu/alignment)then everything works just fine.

A simple strcmp is working fine for me but wanted to run with you guys to see
if i'm missing something here or if anyone has seen this issue before ?

Thanks
Brijesh Singh

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