Rockbox.org home
release
dev builds
extras
themes manual
wiki
device status forums
mailing lists
IRC bugs
patches
dev guide



Rockbox mail archive

Subject: Re: Segfault with Faster MDCT patch and -fPIC

Re: Segfault with Faster MDCT patch and -fPIC

From: Dave Hooper <dave_at_beermex.com>
Date: Fri, 17 Sep 2010 19:01:20 +0100

I think it's hard to tell - let's see what happens without optimisations
(-O0) since the code won't always align easily to the source otherwise.
> On Fri, 17 Sep 2010 16:26:31 +0200
> Slawomir Testowy <slawomir.testowy_at_gmail.com> wrote:
>
>> 2010/9/17 Rafa√ęl Carr√© <rafael.carre_at_gmail.com>:
>> > On Fri, 17 Sep 2010 14:01:48 +0200
>> > Slawomir Testowy <slawomir.testowy_at_gmail.com> wrote:
>> >
>> >> Hi,
>> >>
>> >> thanks for quick response.
>> >>
>> >> 2010/9/17 Rafa√ęl Carr√© <rafael.carre_at_gmail.com>:
>> >> > I think the OP should post .S output of gcc and also give
>> >> > us compiler version and options being used
>> >> >
>> >> > --
>> >> > Rafa√ęl Carr√©
>> >> >
>> >>
>> >> Here it is:
>> >>
>> >>
/opt/freescale/usr/local/gcc-4.1.2-glibc-2.5-nptl-3/arm-none-linux-gnue
>> >> abi/bin/arm-none-linux-gnueabi-gcc --version
>> >> arm-none-linux-gnueabi-gcc (GCC) 4.1.2
>> >> Copyright (C) 2006 Free Software Foundation, Inc.
>> >> This is free software; see the source for copying conditions.
>> >> There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR
>> >> A PARTICULAR PURPOSE.
>> >>
>> >> Exact command line:
>> >>
>> >>
/opt/freescale/usr/local/gcc-4.1.2-glibc-2.5-nptl-3/arm-none-linux-gnue
>> >> abi/bin/arm-none-linux-gnueabi-gcc -std=gnu89 -fPIC -DHAVE_CONFIG_H
>> >> -I. -I./ -O2 -D_ARM_ASSEM_ -fsigned-char -ffast-math
>> >> -fsingle-precision-constant -D_REENTRANT -DUSE_MEMORY_H -MT
>> >> fft-ffmpeg.lo -MD -MP -MF .deps/fft-ffmpeg.Tpo -c fft-ffmpeg.c -o
>> >> fft-ffmpeg.o
>> >>
>> >> Outputs of gcc -S and gcc -E are included in attachments.
>> >>
>> >> I'm afraid I won't be able to test proposed patch today. I'll try
>> >> on Monday.
>> >
>> > I think the patch wouldn't compile on ARM because I missed the ldmia
>> > ordering constraints like Dave mentioned
>> >
>> > otherwise I see that fft8_dispatch only differs on 1 register (-fPIC
>> > use r9 and without it uses r10==sl) but I don't see r10/sl being
>> > used as a pointer.. perhaps it's only done at linking phase?
>> >
>> > BTW building gdb should be as simple as:
>> > ./configure --target=arm-none-linux-gnueabi ; make
>> >
>> > --
>> > Rafa√ęl Carr√©
>> >
>>
>> I managed to build gdbserver + gdb. Here is the stacktrace:
>>
>> Program received signal SIGSEGV, Segmentation fault.
>> 0x0003b3a0 in pass (z_arg=<value optimized out>,
>> STEP_arg=<value optimized out>, n_arg=<value optimized out>)
>> at fft-ffmpeg.c:243
>> 243 w += STEP;
>> (gdb) bt
>> #0 0x0003b3a0 in pass (z_arg=<value optimized out>,
>> STEP_arg=<value optimized out>, n_arg=<value optimized out>)
>> at fft-ffmpeg.c:243
>> #1 0x0003c080 in fft64 (z=0x1b10190) at fft-ffmpeg.c:355
>> #2 0x0003c0b0 in fft128 (z=0x1b10190) at fft-ffmpeg.c:356
>> #3 0x0003c0e0 in fft256 (z=0x1b10190) at fft-ffmpeg.c:357
>> #4 0x0003b924 in ff_fft_calc_c (nbits=<value optimized out>,
>> z=0x1ae2dc0) at fft-ffmpeg.c:370
>> #5 0x0003ad78 in ff_imdct_half (nbits=28199880, output=0x1b100c8,
>> input=<value optimized out>) at mdct-ffmpeg.c:112
>> #6 0x0003b178 in ff_imdct_calc (nbits=28377488, output=0x1afa5c8,
>> input=0x0) at mdct-ffmpeg.c:348
>> #7 0x0003a5ac in mapping0_inverse (vb=0xbef3c670, l=0x1b0b538)
>> at mapping0.c:290
>> #8 0x00033270 in vorbis_synthesis (vb=0xbef3c670, op=<value
>> optimized out>, decodep=1) at synthesis.c:75
>>
>> Unfortunately, most values are optimized out. On Monday, I will
>> rebuild tremor with -O0 and try again.
>
> 'info all-registers' + 'disass $pc-32 $pc+32' can give a hint also
> (from http://ffmpeg.org/bugreports.html)
>
> btw you mentioned TRANSFORM_EQUAL (only used in fft8) in your first mail
> but this time it's in a different function, a different crash?
>
> --
> Rafa√ęl Carr√©
Received on 2010-09-17


Page was last modified "Jan 10 2012" The Rockbox Crew
aaa