Re: libsigsegv progress: SIGSEGV and siginfo_t.si_addr

[Christopher Faylor <cgf-use-the-mailinglist-please at cygwin dot com>]

On Wed, Jul 22, 2009 at 09:18:57PM +0000, Eric Blake wrote:
>POSIX requires that for SIGSEGV and SIGBUS, the si_addr member of siginfo_t be 
>set to the memory address where access failed, and not the address of the 
>instruction attempting to access that address (for SIGILL and SIGFPE, the 
>si_addr field is correct, and for all other signals, the si_addr is unspecified 
>by POSIX so it might as well be the faulting instruction).
>
>Fixing si_addr to contain the correct information will make it possible to 
>patch libsigsegv to avoid installing an SEH handler for all but stack 
>overflow.  (Without this patch, I think I can still patch libsigsegv to honor 
>SIGSEGV, but it will be a much bigger hack of still installing a libsigsegv SEH 
>handler that sniffs the faulting address, then in the SIGSEGV handler refers to 
>the address that was sniffed).
>
>2009-07-22  Eric Blake  <ebb9@byu.net>
>
>	* exceptions.cc (handle_exceptions): Set si_addr according to
>	POSIX for SIGSEGV.
>
>diff --git a/winsup/cygwin/exceptions.cc b/winsup/cygwin/exceptions.cc
>index 7663285..df02489 100644
>--- a/winsup/cygwin/exceptions.cc
>+++ b/winsup/cygwin/exceptions.cc
>@@ -686,7 +686,8 @@ _cygtls::handle_exceptions (EXCEPTION_RECORD *e, 
>exception_list *frame, CONTEXT
>       me.signal_exit (0x80 | si.si_signo);	// Flag signal + core dump
>     }
>
>-  si.si_addr = (void *) in->Eip;
>+  si.si_addr = (si.si_signo == SIGSEGV || si.si_signo == SIGBUS
>+                ? (void *) e->ExceptionInformation[1] : (void *) in->Eip);
>   si.si_errno = si.si_pid = si.si_uid = 0;
>   me.incyg++;
>   sig_send (NULL, si, &me);	// Signal myself

Looks ok.  Please check in.

Thanks for the patch.

cgf

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