Saving errno around signal handlers

[Florian Weimer]

On 02/28/2014 05:49 PM, Richard Henderson wrote:
> On 02/28/2014 03:49 AM, Florian Weimer wrote:
>>
>> In all cases (kernel and glibc implementation), we can use a tail call to make
>> sure that the stack layout looks like it is at present (at least on
>> architectures with an available callee-saved register), and we would not have
>> to adjust GDB and other tools.
>
> How's that?  A tail call would not be able to "restore" anything afterward.

We already have the restorer that calls sigreturn, and could add

         movq    errno@gottpoff(%rip), %rdi
         movl    %r12d, %fs:(%rdi)

right before that.

-- 
Florian Weimer / Red Hat Product Security Team