On Tue, Sep 09, 2014 at 07:17:19PM -0300, Mauricio Faria de Oliveira wrote: > This fixes a segmentation fault in the system call's error handling path with > dynamically-linked binaries on PowerPC64 little endian. The system call stub > wasn't loading up r2 with the appropriate TOC value in its global entry point. > > The r2 setup code comes from the FUNC_START macro in gcc [1] and an equivalent > one can also be found in the LOCALENTRY macro in glibc [2]. > > On the ELFv2 ABI (see [1]): > - The global entry point is expected to load up r2 with the appropriate TOC > value for this function. > - The local entry point expects r2 to be set up to the current TOC. > > The problem happened with dynamically-linked binaries because: > - the system call is an indirect call (via global entry point) from the > binary > to the shared library, landing in the syscall stub (which didn't load up > r2 > with the TOC of the shared library) > - its branch to __syscall_error is a direct call (via local entry point) > within > the shared library, landing in the function (which expects r2 to be set up > to > that TOC) > - when the function attempts to store errno (in an address relative to the > TOC), > that address incorrectly pointed to a read-only segment -- segmentation > fault. > > The problem didn't happen with statically-linked binaries because the TOC > value > wasn't different on that case. > > Thanks and credits to Alan Modra and Ulrich Weigand, for helping with this and > pointing out the solution. > > [1] https://gcc.gnu.org/ml/gcc-patches/2013-11/msg01141.html > [2] https://www.sourceware.org/ml/libc-alpha/2013-11/msg00315.html > > Signed-off-by: Mauricio Faria de Oliveira <mauri...@linux.vnet.ibm.com> > --- > usr/klibc/arch/ppc64/sysstub.ph | 3 +++ > 1 files changed, 3 insertions(+), 0 deletions(-) > > diff --git a/usr/klibc/arch/ppc64/sysstub.ph b/usr/klibc/arch/ppc64/sysstub.ph > index b3f6e38..a0c6d41 100644 > --- a/usr/klibc/arch/ppc64/sysstub.ph > +++ b/usr/klibc/arch/ppc64/sysstub.ph > @@ -18,6 +18,9 @@ sub make_sysstub($$$$$@) { > #if _CALL_ELF == 2 > .type ${fname},\@function > ${fname}: > +0: addis 2,12,(.TOC.-0b)\@ha > + addi 2,2,(.TOC.-0b)\@l > + .localentry ${fname},.-${fname} > #else > .section ".opd","aw" > .balign 8
Thanks for the patch, I confirm it fixes the problem. -- Aurelien Jarno GPG: 4096R/1DDD8C9B aurel...@aurel32.net http://www.aurel32.net -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
