* musl segfaulting when compiled with -O2
@ 2017-03-07 20:32 Breno Leitao
2017-03-07 20:39 ` Rich Felker
0 siblings, 1 reply; 8+ messages in thread
From: Breno Leitao @ 2017-03-07 20:32 UTC (permalink / raw)
To: musl
Musl package on Debian on ppc64le is broken.
When running any software with it, it segfaults. Doing a little bit of
debugging I found that libc.so is broken.
I got the upstream code, and found that the problme is also
reproducible.
I found that the problem only happen when compiling with -O2 and -O3. If
I compile musl with -O1 or -O0, the problm does not happen.
This is the bt of the code that crashes:
(gdb) bt
#0 0x0000000148b84dc0 in ?? ()
#1 0x0000000048bdb8dc in _dlstart_c (sp=0x3fffc33294b0, dynv=<optimized out>) at ldso/dlstart.c:147
#2 0x0000000048bdebe0 in _dlstart ()
(gdb) up
#1 0x0000000048bdb8dc in _dlstart_c (sp=0x3fffc33294b0, dynv=<optimized out>) at ldso/dlstart.c:147
147 dls2((void *)base, sp);
$ gcc --version
gcc (Debian 6.3.0-5) 6.3.0 20170124
Not sure if this is a GCC issue or a musl issue now.
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: musl segfaulting when compiled with -O2
2017-03-07 20:32 musl segfaulting when compiled with -O2 Breno Leitao
@ 2017-03-07 20:39 ` Rich Felker
2017-03-07 20:55 ` Breno Leitao
0 siblings, 1 reply; 8+ messages in thread
From: Rich Felker @ 2017-03-07 20:39 UTC (permalink / raw)
To: musl
On Tue, Mar 07, 2017 at 05:32:35PM -0300, Breno Leitao wrote:
> Musl package on Debian on ppc64le is broken.
>
> When running any software with it, it segfaults. Doing a little bit of
> debugging I found that libc.so is broken.
>
> I got the upstream code, and found that the problme is also
> reproducible.
>
> I found that the problem only happen when compiling with -O2 and -O3. If
> I compile musl with -O1 or -O0, the problm does not happen.
>
> This is the bt of the code that crashes:
>
> (gdb) bt
> #0 0x0000000148b84dc0 in ?? ()
> #1 0x0000000048bdb8dc in _dlstart_c (sp=0x3fffc33294b0, dynv=<optimized out>) at ldso/dlstart.c:147
> #2 0x0000000048bdebe0 in _dlstart ()
>
> (gdb) up
> #1 0x0000000048bdb8dc in _dlstart_c (sp=0x3fffc33294b0, dynv=<optimized out>) at ldso/dlstart.c:147
> 147 dls2((void *)base, sp);
>
> $ gcc --version
> gcc (Debian 6.3.0-5) 6.3.0 20170124
>
> Not sure if this is a GCC issue or a musl issue now.
Can you post the crashing libc.so somewhere? Depending on how they're
building it, the problem could be in various different places. A
glibc-targeted powerpc* gcc is not suitable for compiling musl, since
it has various ABI mismatches, but that's probably not what you're
seeing here even if one was used.
Rich
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: musl segfaulting when compiled with -O2
2017-03-07 20:39 ` Rich Felker
@ 2017-03-07 20:55 ` Breno Leitao
2017-03-07 21:45 ` Rich Felker
0 siblings, 1 reply; 8+ messages in thread
From: Breno Leitao @ 2017-03-07 20:55 UTC (permalink / raw)
To: musl
Hi Rich,
On Tue, Mar 07, 2017 at 03:39:05PM -0500, Rich Felker wrote:
> On Tue, Mar 07, 2017 at 05:32:35PM -0300, Breno Leitao wrote:
> > Musl package on Debian on ppc64le is broken.
> >
> > When running any software with it, it segfaults. Doing a little bit of
> > debugging I found that libc.so is broken.
> >
> > I got the upstream code, and found that the problme is also
> > reproducible.
> >
> > I found that the problem only happen when compiling with -O2 and -O3. If
> > I compile musl with -O1 or -O0, the problm does not happen.
> >
> > This is the bt of the code that crashes:
> >
> > (gdb) bt
> > #0 0x0000000148b84dc0 in ?? ()
> > #1 0x0000000048bdb8dc in _dlstart_c (sp=0x3fffc33294b0, dynv=<optimized out>) at ldso/dlstart.c:147
> > #2 0x0000000048bdebe0 in _dlstart ()
> >
> > (gdb) up
> > #1 0x0000000048bdb8dc in _dlstart_c (sp=0x3fffc33294b0, dynv=<optimized out>) at ldso/dlstart.c:147
> > 147 dls2((void *)base, sp);
> >
> > $ gcc --version
> > gcc (Debian 6.3.0-5) 6.3.0 20170124
> >
> > Not sure if this is a GCC issue or a musl issue now.
>
> Can you post the crashing libc.so somewhere? Depending on how they're
> building it, the problem could be in various different places. A
> glibc-targeted powerpc* gcc is not suitable for compiling musl, since
> it has various ABI mismatches, but that's probably not what you're
> seeing here even if one was used.
Sure. You can grab it directly from Debian:
$ wget http://cdn-fastly.deb.debian.org/debian/pool/main/m/musl/musl_1.1.16-2_ppc64el.deb
$ dpkg-deb -x musl_1.1.16-2_ppc64el.deb .
$ lib/powerpc64le-linux-musl/libc.so
[2] 25672 segmentation fault (core dumped) lib/powerpc64le-linux-musl/libc.so
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: musl segfaulting when compiled with -O2
2017-03-07 20:55 ` Breno Leitao
@ 2017-03-07 21:45 ` Rich Felker
2017-03-08 1:18 ` Szabolcs Nagy
0 siblings, 1 reply; 8+ messages in thread
From: Rich Felker @ 2017-03-07 21:45 UTC (permalink / raw)
To: musl
On Tue, Mar 07, 2017 at 05:55:29PM -0300, Breno Leitao wrote:
> Hi Rich,
>
> On Tue, Mar 07, 2017 at 03:39:05PM -0500, Rich Felker wrote:
> > On Tue, Mar 07, 2017 at 05:32:35PM -0300, Breno Leitao wrote:
> > > Musl package on Debian on ppc64le is broken.
> > >
> > > When running any software with it, it segfaults. Doing a little bit of
> > > debugging I found that libc.so is broken.
> > >
> > > I got the upstream code, and found that the problme is also
> > > reproducible.
> > >
> > > I found that the problem only happen when compiling with -O2 and -O3. If
> > > I compile musl with -O1 or -O0, the problm does not happen.
> > >
> > > This is the bt of the code that crashes:
> > >
> > > (gdb) bt
> > > #0 0x0000000148b84dc0 in ?? ()
> > > #1 0x0000000048bdb8dc in _dlstart_c (sp=0x3fffc33294b0, dynv=<optimized out>) at ldso/dlstart.c:147
> > > #2 0x0000000048bdebe0 in _dlstart ()
> > >
> > > (gdb) up
> > > #1 0x0000000048bdb8dc in _dlstart_c (sp=0x3fffc33294b0, dynv=<optimized out>) at ldso/dlstart.c:147
> > > 147 dls2((void *)base, sp);
> > >
> > > $ gcc --version
> > > gcc (Debian 6.3.0-5) 6.3.0 20170124
> > >
> > > Not sure if this is a GCC issue or a musl issue now.
> >
> > Can you post the crashing libc.so somewhere? Depending on how they're
> > building it, the problem could be in various different places. A
> > glibc-targeted powerpc* gcc is not suitable for compiling musl, since
> > it has various ABI mismatches, but that's probably not what you're
> > seeing here even if one was used.
>
> Sure. You can grab it directly from Debian:
>
> $ wget http://cdn-fastly.deb.debian.org/debian/pool/main/m/musl/musl_1.1.16-2_ppc64el.deb
>
> $ dpkg-deb -x musl_1.1.16-2_ppc64el.deb .
>
> $ lib/powerpc64le-linux-musl/libc.so
> [2] 25672 segmentation fault (core dumped) lib/powerpc64le-linux-musl/libc.so
Can you do a register dump and a dissassembly dump and around the
point that crashes? The Debian package is fully stripped (lacks debug
symbols) so it's hard to follow what it's doing, but I didn't see
anything obviously wrong.
Rich
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: musl segfaulting when compiled with -O2
2017-03-07 21:45 ` Rich Felker
@ 2017-03-08 1:18 ` Szabolcs Nagy
2017-03-08 2:28 ` Rich Felker
0 siblings, 1 reply; 8+ messages in thread
From: Szabolcs Nagy @ 2017-03-08 1:18 UTC (permalink / raw)
To: musl
* Rich Felker <dalias@libc.org> [2017-03-07 16:45:40 -0500]:
> On Tue, Mar 07, 2017 at 05:55:29PM -0300, Breno Leitao wrote:
> > $ wget http://cdn-fastly.deb.debian.org/debian/pool/main/m/musl/musl_1.1.16-2_ppc64el.deb
> >
> > $ dpkg-deb -x musl_1.1.16-2_ppc64el.deb .
> >
> > $ lib/powerpc64le-linux-musl/libc.so
> > [2] 25672 segmentation fault (core dumped) lib/powerpc64le-linux-musl/libc.so
>
> Can you do a register dump and a dissassembly dump and around the
> point that crashes? The Debian package is fully stripped (lacks debug
> symbols) so it's hard to follow what it's doing, but I didn't see
> anything obviously wrong.
>
> Rich
i used qemu-ppc64le -singlestep -d in_asm,cpu to debug this
the relevant code is the end of _dlstart_c:
...
8c574: 09 00 00 48 bl 8c57c <writev+0x28c>
8c578: 28 98 fa ff fsub f31,f26,f19
8c57c: a6 02 48 7d mflr r10
8c580: 00 00 2a 81 lwz r9,0(r10)
8c584: 14 52 29 7d add r9,r9,r10
8c588: a6 03 29 7d mtctr r9
8c58c: 18 00 41 f8 std r2,24(r1)
8c590: 78 3b e4 7c mr r4,r7
8c594: 78 4b 2c 7d mr r12,r9
8c598: 21 04 80 4e bctrl
it's a pc relative address load and jump (to call __dls2):
bl 1f
data // data == 0xfffa9828
1: mflr r10 // r10 = &data == 0x8c57c
lwz r9,0(r10) // r9 = *r10 (== data)
add r9,r9,r10 // r9 += r10 (== 0xfffa9828+0x8c57c = 0x100035da0)
mtctr r9 // ctr = r9 (== 0x100035da0)
std r2,24(r1)
mr r4,r7
mr r12,r9
bctrl // ctr(r12,r4)
it seems __dls2 is at 0x35da0 so the pc relative data
should have been signextended.
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: musl segfaulting when compiled with -O2
2017-03-08 1:18 ` Szabolcs Nagy
@ 2017-03-08 2:28 ` Rich Felker
2017-03-08 14:19 ` Breno Leitao
0 siblings, 1 reply; 8+ messages in thread
From: Rich Felker @ 2017-03-08 2:28 UTC (permalink / raw)
To: musl
[-- Attachment #1: Type: text/plain, Size: 1909 bytes --]
On Wed, Mar 08, 2017 at 02:18:43AM +0100, Szabolcs Nagy wrote:
> * Rich Felker <dalias@libc.org> [2017-03-07 16:45:40 -0500]:
> > On Tue, Mar 07, 2017 at 05:55:29PM -0300, Breno Leitao wrote:
> > > $ wget http://cdn-fastly.deb.debian.org/debian/pool/main/m/musl/musl_1.1.16-2_ppc64el.deb
> > >
> > > $ dpkg-deb -x musl_1.1.16-2_ppc64el.deb .
> > >
> > > $ lib/powerpc64le-linux-musl/libc.so
> > > [2] 25672 segmentation fault (core dumped) lib/powerpc64le-linux-musl/libc.so
> >
> > Can you do a register dump and a dissassembly dump and around the
> > point that crashes? The Debian package is fully stripped (lacks debug
> > symbols) so it's hard to follow what it's doing, but I didn't see
> > anything obviously wrong.
> >
> > Rich
>
> i used qemu-ppc64le -singlestep -d in_asm,cpu to debug this
>
> the relevant code is the end of _dlstart_c:
> ....
> 8c574: 09 00 00 48 bl 8c57c <writev+0x28c>
> 8c578: 28 98 fa ff fsub f31,f26,f19
> 8c57c: a6 02 48 7d mflr r10
> 8c580: 00 00 2a 81 lwz r9,0(r10)
> 8c584: 14 52 29 7d add r9,r9,r10
> 8c588: a6 03 29 7d mtctr r9
> 8c58c: 18 00 41 f8 std r2,24(r1)
> 8c590: 78 3b e4 7c mr r4,r7
> 8c594: 78 4b 2c 7d mr r12,r9
> 8c598: 21 04 80 4e bctrl
>
> it's a pc relative address load and jump (to call __dls2):
>
> bl 1f
> data // data == 0xfffa9828
> 1: mflr r10 // r10 = &data == 0x8c57c
> lwz r9,0(r10) // r9 = *r10 (== data)
> add r9,r9,r10 // r9 += r10 (== 0xfffa9828+0x8c57c = 0x100035da0)
> mtctr r9 // ctr = r9 (== 0x100035da0)
> std r2,24(r1)
> mr r4,r7
> mr r12,r9
> bctrl // ctr(r12,r4)
>
> it seems __dls2 is at 0x35da0 so the pc relative data
> should have been signextended.
Does the attached patch fix it?
Rich
[-- Attachment #2: ppc64_crash.diff --]
[-- Type: text/plain, Size: 357 bytes --]
diff --git a/arch/powerpc64/reloc.h b/arch/powerpc64/reloc.h
index e1bad00..faf70ac 100644
--- a/arch/powerpc64/reloc.h
+++ b/arch/powerpc64/reloc.h
@@ -27,6 +27,6 @@
" bl 1f \n" \
" .long " #sym "-. \n" \
"1: mflr %1 \n" \
- " lwz %0, 0(%1) \n" \
+ " lwa %0, 0(%1) \n" \
" add %0, %0, %1 \n" \
: "=r"(*(fp)), "=r"((long){0}) : : "memory", "lr" )
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: musl segfaulting when compiled with -O2
2017-03-08 2:28 ` Rich Felker
@ 2017-03-08 14:19 ` Breno Leitao
2017-03-08 18:39 ` Rich Felker
0 siblings, 1 reply; 8+ messages in thread
From: Breno Leitao @ 2017-03-08 14:19 UTC (permalink / raw)
To: musl
Hi Rich,
On Tue, Mar 07, 2017 at 09:28:27PM -0500, Rich Felker wrote:
> Does the attached patch fix it?
Yes. I just tested on my machine, and the problem is not reproducible
anymore.
Thanks!
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: musl segfaulting when compiled with -O2
2017-03-08 14:19 ` Breno Leitao
@ 2017-03-08 18:39 ` Rich Felker
0 siblings, 0 replies; 8+ messages in thread
From: Rich Felker @ 2017-03-08 18:39 UTC (permalink / raw)
To: musl
On Wed, Mar 08, 2017 at 11:19:10AM -0300, Breno Leitao wrote:
> Hi Rich,
>
> On Tue, Mar 07, 2017 at 09:28:27PM -0500, Rich Felker wrote:
> > Does the attached patch fix it?
>
> Yes. I just tested on my machine, and the problem is not reproducible
> anymore.
>
> Thanks!
Thanks for testing/feedback. Committing.
Rich
^ permalink raw reply [flat|nested] 8+ messages in thread
end of thread, other threads:[~2017-03-08 18:39 UTC | newest]
Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2017-03-07 20:32 musl segfaulting when compiled with -O2 Breno Leitao
2017-03-07 20:39 ` Rich Felker
2017-03-07 20:55 ` Breno Leitao
2017-03-07 21:45 ` Rich Felker
2017-03-08 1:18 ` Szabolcs Nagy
2017-03-08 2:28 ` Rich Felker
2017-03-08 14:19 ` Breno Leitao
2017-03-08 18:39 ` Rich Felker
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