https://sourceware.org/bugzilla/show_bug.cgi?id=30697
Bug ID: 30697
Summary: bfd TLS handling (with local-dynamic model) broken
with large GOT causing Python 3.12 to segfault
Product: binutils
Version: 2.40
Status: NEW
Severity: normal
Priority: P2
Component: ld
Assignee: unassigned at sourceware dot org
Reporter: sam at gentoo dot org
CC: amonakov at gmail dot com, arsen at aarsen dot me,
toolchain at gentoo dot org
Target Milestone: ---
Originally reported downstream in Gentoo at https://bugs.gentoo.org/909544 and
then to Python at https://github.com/python/cpython/issues/106428.
* With GCC 12, Python 3.12 builds fine on ppc32. With GCC 13, Python 3.12
segfaults.
* Python 3.12 bisect:
https://github.com/python/cpython/commit/f8abfa331421e2c28388c5162f37820495e3c2ee
(they started using TLS)
* GCC 13 bisect:
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=1d561e1851c466a4952081caef17747781609b00
(ipa-visibility: Optimize TLS access)
The latter commit co-author, Alexander Monakov, helpfully analysed the bug
downstream in Gentoo (https://bugs.gentoo.org/909544#c12):
>I can reproduce it. It's a BFD linker bug. With another linker (CC='gcc
>-fuse-ld=gold') it works fine. The linker seems to >mishandle one of these
>relocations when GOT is big:
>
> addis 3,3,_Py_tss_tstate@dtprel@ha
> addi 3,3,_Py_tss_tstate@dtprel@l
>
>Single-stepping in GDB shows that the resulting value of r3 differs from
>actual address of _Py_tss_tstate (as computed by >GDB, which in principle
>could also be wrong) by 0x1000.
>
>You can reproduce it with any GCC version by specifying TLS model in python
>source explicitly:
>
>diff --git a/Python/pystate.c b/Python/pystate.c
>index cdd975f..ef8b9f6 100644
>--- a/Python/pystate.c
>+++ b/Python/pystate.c
>@@ -63,6 +63,7 @@ extern "C" {
>
>
> #ifdef HAVE_THREAD_LOCAL
>+__attribute__((tls_model("local-dynamic")))
> _Py_thread_local PyThreadState *_Py_tss_tstate = NULL;
> #endif
>
>
>(or you can specify the "global-dynamic" model explicitly to paper over the
>linker bug with new GCC)
I'll upload a (large) reproducer shortly.
--
You are receiving this mail because:
You are on the CC list for the bug.
