[x264-devel] Crash due to unaligned pointer on SPARC
Doctor Jones
document5 at lycos.com
Thu Jan 29 06:37:16 CET 2009
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Under my Debian Lenny RC1 SPARC machine, every snapshot of x264 that I have tried crashes with "Bus error" when attempting to encode a file. This happens both with the shared library (through mencoder and ffmpeg at least) and the x264 command line encoder.
I think I have tracked down the issue. I'm new to this, so if I'm incredibly wrong don't hesitate to say it. I think it's related to an unaligned memory access. I've been poking around with gdb for a while (various gdb outputs attached at bottom), and the crash looks like this:
Of particular note is that s->p is not properly byte aligned at the time of the crash. I believe this is the cause.
[Thread debugging using libthread_db enabled]
x264 [info]: using cpu capabilities: none!
p_bitstream is 0xf793e020
x264 [info]: profile Main, level 3.0
[New Thread 0xf7f93350 (LWP 4644)]
Program received signal SIGBUS, Bus error.
[Switching to Thread 0xf7f93350 (LWP 4644)]
0x00071094 in x264_sps_write (s=0xa07c8, sps=0xa0808) at ./common/bs.h:123
123 *(uint32_t*)s->p = endian_fix( s->cur_bits );
(gdb) print s->p
$1 = (uint8_t *) 0xf793e209 ""
(gdb) bt
#0 0x00071094 in x264_sps_write (s=0xa07c8, sps=0xa0808) at ./common/bs.h:123
#1 0x0001fa8c in x264_encoder_encode (h=0xa0300, pp_nal=0xfff6721c, pi_nal=0xfff67218, pic_in=0xfff67580,
pic_out=0xfff67220) at encoder/encoder.c:1580
#2 0x000121a8 in Encode_frame (h=0xa0300, hout=0xa0008, pic=0xfff67580) at x264.c:757
#3 0x00012eb0 in main (argc=<value optimized out>, argv=0xfff67904) at x264.c:841
(gdb) disass $pc-32 $pc+32
Dump of assembler code from 0x71074 to 0x710b4:
0x00071074 <x264_sps_write+2196>: ld [ %i0 + 0xc ], %g1
0x00071078 <x264_sps_write+2200>: sll %g1, %g3, %g1
0x0007107c <x264_sps_write+2204>: st %g1, [ %i0 + 0xc ]
0x00071080 <x264_sps_write+2208>: sub %g4, %g3, %g1
0x00071084 <x264_sps_write+2212>: b 0x710b4 <x264_sps_write+2260>
0x00071088 <x264_sps_write+2216>: st %g1, [ %i0 + 0x10 ]
0x0007108c <x264_sps_write+2220>: sll %g1, %g4, %g1
0x00071090 <x264_sps_write+2224>: ld [ %i0 + 4 ], %g2
0x00071094 <x264_sps_write+2228>: st %g1, [ %g2 ]
0x00071098 <x264_sps_write+2232>: ld [ %i0 + 4 ], %g1
0x0007109c <x264_sps_write+2236>: add %g1, 4, %g1
0x000710a0 <x264_sps_write+2240>: st %g1, [ %i0 + 4 ]
0x000710a4 <x264_sps_write+2244>: clr [ %i0 + 0xc ]
0x000710a8 <x264_sps_write+2248>: sub %g4, %g3, %g1
0x000710ac <x264_sps_write+2252>: add %g1, 0x20, %g1
0x000710b0 <x264_sps_write+2256>: st %g1, [ %i0 + 0x10 ]
End of assembler dump.
(gdb) info all-registers
g0 0x0 0
g1 0x4d401e9a 1296047770
g2 0xf793e209 -141303287
g3 0x2 2
g4 0x1 1
g5 0x0 0
g6 0x3300474c 855656268
g7 0xf7f93350 -134663344
o0 0x99c9c 629916
o1 0x0 0
o2 0x0 0
o3 0x0 0
o4 0x7 7
o5 0x7 7
sp 0xfff67030 0xfff67030
o7 0x707e8 460776
l0 0x0 0
l1 0x0 0
l2 0x0 0
l3 0x0 0
l4 0x0 0
l5 0x0 0
l6 0x0 0
---Type <return> to continue, or q <return> to quit---
l7 0x0 0
i0 0xa07c8 657352
i1 0xa0808 657416
i2 0x3 3
i3 0xa0ce4 658660
i4 0x0 0
i5 0x0 0
fp 0xfff670a0 0xfff670a0
i7 0x1fa84 129668
f0 2.81690598 (raw 0x40344830)
f1 1.85467776e-29 (raw 0x0fbc1630)
f2 -nan(0x7fffff) (raw 0xffffffff)
f3 -nan(0x7fffff) (raw 0xffffffff)
f4 -nan(0x7fffff) (raw 0xffffffff)
f5 -nan(0x7fffff) (raw 0xffffffff)
f6 1.69999993 (raw 0x3fd99999)
f7 -0 (raw 0x80000000)
f8 1.875 (raw 0x3ff00000)
f9 0 (raw 0x00000000)
f10 1.875 (raw 0x3ff00000)
f11 0 (raw 0x00000000)
f12 0.0144915329 (raw 0x3c6d6de5)
f13 7.57048119e+34 (raw 0x79694891)
---Type <return> to continue, or q <return> to quit---
f14 0.408562958 (raw 0x3ed12f2a)
f15 2.18561172 (raw 0x400be110)
f16 0.408563018 (raw 0x3ed12f2c)
f17 -1.90701462e-32 (raw 0x8ac60925)
f18 0 (raw 0x00000000)
f19 0 (raw 0x00000000)
f20 -0.00686295424 (raw 0xbbe0e2a2)
f21 -1.05229209e+12 (raw 0xd375017f)
f22 0.46875 (raw 0x3ef00000)
f23 0 (raw 0x00000000)
f24 0.771456778 (raw 0x3f457e31)
f25 -2.98926663e+31 (raw 0xf3bca635)
f26 1.63148248 (raw 0x3fd0d46b)
f27 3.40224056e+14 (raw 0x579ab74b)
f28 0.0427142903 (raw 0x3d2ef52e)
f29 3.14914689e+30 (raw 0x721efdc5)
f30 1.81706607 (raw 0x3fe8959f)
f31 -2.90170261e+12 (raw 0xd428e6bd)
y 0x0 0
psr 0xff000082 [ #1 S #24 #25 #26 #27 #28 #29 #30 #31 ]
wim 0x0 0
tbr 0x0 0
pc 0x71094 0x71094 <x264_sps_write+2228>
---Type <return> to continue, or q <return> to quit---
npc 0x71098 0x71098 <x264_sps_write+2232>
fsr 0x0 [ ]
csr 0x0 0
d0 20.281983359737012 (raw 0x403448300fbc1630)
d2 -nan(0xfffffffffffff) (raw 0xffffffffffffffff)
d4 -nan(0xfffffffffffff) (raw 0xffffffffffffffff)
d6 0.39999997615814209 (raw 0x3fd9999980000000)
d8 1 (raw 0x3ff0000000000000)
d10 1 (raw 0x3ff0000000000000)
d12 1.276291691662309e-17 (raw 0x3c6d6de579694891)
d14 4.0970417109975149e-06 (raw 0x3ed12f2a400be110)
d16 4.0970500488921436e-06 (raw 0x3ed12f2c8ac60925)
d18 0 (raw 0x0000000000000000)
d20 -2.8604805813190531e-20 (raw 0xbbe0e2a2d375017f)
d22 1.52587890625e-05 (raw 0x3ef0000000000000)
d24 0.00065591277186633509 (raw 0x3f457e31f3bca635)
d26 0.26296504550088134 (raw 0x3fd0d46b579ab74b)
d28 5.4991993104000338e-14 (raw 0x3d2ef52e721efdc5)
d30 0.76826468884902221 (raw 0x3fe8959fd428e6bd)
But where does it go wrong? Well, it looks like it's here:
Old value = (uint8_t *) 0xf78f2204 ".00"
New value = (uint8_t *) 0xf78f2208 ""
x264_sei_version_write (h=<value optimized out>, s=0xa07c8) at ./common/bs.h:125
125 s->cur_bits = i_bits;
(gdb)
Continuing.
Watchpoint 9: s->p
Old value = (uint8_t *) 0xf78f2208 "\200"
New value = (uint8_t *) 0xf78f2209 ""
x264_sei_version_write (h=<value optimized out>, s=0xa07c8) at ./common/bs.h:92
92 s->i_left = WORD_SIZE*8;
That is, it looks like it's a result of
s->p += WORD_SIZE - s->i_left / 8;
in bs_flush (common/bs.h). This function includes a note that it will result in a stream that is no longer 32/64 bit aligned, but what can be done about it to prevent this crash on SPARC? I don't know enough about the code. Is there any reasonable way to maintain alignment?
My SPARC box has gdb and various other tools if anyone needs any more information.
Thanks.
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