sigsegv on s390 only giving start address of page in segv handler

[Bruno Haible]

Hi Christoph,

When you wrote to <bug-libsigsegv-antispam at antispam.gnu.org> you didn't remove
the "antispam" words from the address.

>     libsigsegv doesn't cope well with s390 at the moment. This is caused
> by the fact, that linux masks the address for sigsegv:
> 
>   mm/fault.c:#define __FAIL_ADDR_MASK 0x7ffff000
> 
> So the last 12 bit of information are lost.

Thanks for the analysis. Indeed at least the 'sigsegv1' test will fail in this
situation.

Have you reported the problem to the linux-kernel mailing list, or to the
maintainers of the s390 part of Linux?

> Forcing libsigsegv to use 
> POSIX signal handlers othewise makes a library that passes all the tests
> apart from the exact fault location.

That sounds promising, if the kernel problem was fixed.

> Now I'm wondering of software depending on libsigsegv won't work on s390
> or maybe the correct page is still enough information for dependencies
> like clisp to work -- in that case a "fix" would be rather easy.

clisp (and probably other software too) will compile and work also when
the installed <sigsegv.h> file does not define HAVE_SIGSEGV_RECOVERY or
HAVE_STACK_OVERFLOW_RECOVERY. But the functionality will be a bit degraded.
For clisp, it means that generational GC will not be compiled into clisp
if HAVE_SIGSEGV_RECOVERY is not defined, and endless recursions may cause
a crash if HAVE_STACK_OVERFLOW_RECOVERY is not defined.

Bruno
-- 
In memoriam Marie Politzer <http://fr.wikipedia.org/wiki/Marie_Politzer>