Revert Intel CET changes to __jmp_buf_tag (Bug 22743)

In commit cba595c350e52194e10c0006732e1991e3d0803b and commit
f81ddabffd76ac9dd600b02adbf3e1dac4bb10ec, ABI compatibility with
applications was broken by increasing the size of the on-stack
allocated __pthread_unwind_buf_t beyond the oringal size.
Applications only have the origianl space available for
__pthread_unwind_register, and __pthread_unwind_next to use,
any increase in the size of __pthread_unwind_buf_t causes these
functions to write beyond the original structure into other
on-stack variables leading to segmentation faults in common
applications like vlc. The only workaround is to version those
functions which operate on the old sized objects, but this must
happen in glibc 2.28.

Thank you to Andrew Senkevich, H.J. Lu, and Aurelien Jarno, for
submitting reports and tracking the issue down.

The commit reverts the above mentioned commits and testing on
x86_64 shows that the ABI compatibility is restored. A tst-cleanup1
regression test linked with an older glibc now passes when run
with the newly built glibc. Previously a tst-cleanup1 linked with
an older glibc would segfault when run with an affected glibc build.

Tested on x86_64 with no regressions.

Signed-off-by: Carlos O'Donell <carlos@redhat.com>

1 files changed, 0 insertions, 3 deletions

diff --git a/nptl/descr.h b/nptl/descr.h
index 1cc6b09d1e..64ba29e1cb 100644
--- a/nptl/descr.h
+++ b/nptl/descr.h
@@ -65,9 +65,6 @@ struct pthread_unwind_buf
   {
     __jmp_buf jmp_buf;
     int mask_was_saved;
-#ifdef NEED_SAVED_MASK_IN_CANCEL_JMP_BUF
-    __sigset_t saved_mask;
-#endif
   } cancel_jmp_buf[1];
 
   union