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Re: Saving errno around signal handlers
- From: Rich Felker <dalias at aerifal dot cx>
- To: Florian Weimer <fweimer at redhat dot com>
- Cc: Richard Henderson <rth at twiddle dot net>, GNU C Library <libc-alpha at sourceware dot org>
- Date: Fri, 28 Feb 2014 19:31:41 -0500
- Subject: Re: Saving errno around signal handlers
- Authentication-results: sourceware.org; auth=none
- References: <531077D9 dot 2000308 at redhat dot com> <5310BE05 dot 7090606 at twiddle dot net> <5310C04E dot 9090009 at redhat dot com>
On Fri, Feb 28, 2014 at 05:58:54PM +0100, Florian Weimer wrote:
> 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.
This does not support nested signal handlers. The saved errno must be
on the stack frame of the trampoline calling the real signal handler,
not a fixed TLS location.
Rich