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Message-ID: <20170308022827.GW1520@brightrain.aerifal.cx>
Date: Tue, 7 Mar 2017 21:28:27 -0500
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: musl segfaulting when compiled with -O2
On Wed, Mar 08, 2017 at 02:18:43AM +0100, Szabolcs Nagy wrote:
> * Rich Felker <dalias@...c.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
View attachment "ppc64_crash.diff" of type "text/plain" (358 bytes)
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