Re: [PATCH] Revert Intel CET changes to __jmp_buf_tag (Bug 22743)

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Wed, Jan 24, 2018 at 8:53 PM, Carlos O'Donell <carlos@redhat.com> wrote:
> On 01/24/2018 05:48 PM, Dmitry V. Levin wrote:
>> I'm afraid by Monday it will be too late for 2.27 as we will get very
>> little testing before the release.
>  Before reverting:
>
> [carlos@athas tst-cleanup1]$ /home/carlos/build/glibc/elf/ld.so --library-path /home/carlos/build/glibc:/home/carlos/build/glibc/elf:/home/carlos/build/glibc/dlfcn:/home/carlos/build/glibc/nptl ./tst-cleanup1
> ch (3)
> ch (2)
> ch (1)
> Didn't expect signal from child: got `Segmentation fault'
>
> After reverting:
>
> [carlos@athas tst-cleanup1]$ /home/carlos/build/glibc-reverted/elf/ld.so --library-path /home/carlos/build/glibc-reverted:/home/carlos/build/glibc-reverted/elf:/home/carlos/build/glibc-reverted/dlfcn:/home/carlos/build/glibc-reverted/nptl ./tst-cleanup1
> ch (3)
> ch (2)
> ch (1)
>
> ~~~ Commit message ~~~
> 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>
> ~~~
>
> Patch attached.
>
> OK to commit?
>
> This fixes the last blocker for glibc 2.27.

Please don't revert my patch.  Please try this patch:

https://sourceware.org/git/?p=glibc.git;a=commit;h=4b7fc470a6740808b41502d7431f91805e272d26

instead.  I will clean it up and submit it tomorrow.

Thanks.


-- 
H.J.