* 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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