Re: [Gcl-devel] Re: trapping segfaults on mac os x

[Camm Maguire]

Greetings, and thank you again so much!  Am checking it out now.  It
looks like it might work on mingw too.

Take care,

Bruno Haible <address@hidden> writes:

> Hi Camm,
>
>> The mac does not
>> appear to be trapping SIGSEGV via sigaction in the standard way (for
>> SGC garbage collection).  Under gdb, the process appears to receive
>> something straight from the kernel, EXC_BAD_ACCESS, and does not
>> trigger or enter the handler at all.  Do you have any suggestion here?
>
> Use GNU libsigsegv <http://www.gnu.org/software/libsigsegv/>. It's made
> for this purpose.
>
>> Do you know why the following simple program does not call
>> the handler on macosx?
>> 
>> =============================================================================
>> f.c
>> =============================================================================
>> #include <sys/mman.h>
>> #include <stdio.h>
>> #include <signal.h>
>> 
>> void
>> h(int s,long c,void *scp,char *a) {
>> 
>>   printf("foo\n");
>> 
>> }
>> 
>> int
>> main(int argc,char * argv[]) {
>> 
>>   char b1[4096*2],*b=b1;
>>   struct sigaction siga;
>> 
>>   b=(char *)(((unsigned long)b+4095) & ~4095);
>>   siga.sa_handler=(void *)h;
>>   siga.sa_flags=SA_RESTART|SA_SIGINFO|SA_RESETHAND;
>>   sigemptyset(&siga.sa_mask);
>>   sigaction(SIGSEGV,&siga,0);
>>   mprotect(b,sizeof(b),PROT_READ);
>>   b[0]=1;
>>   return 0;
>> }
>> =============================================================================
>
> Short explanation: Things just don't work this way on MacOS X.
>
> Long explanation: When a fault occurs in MacOS X, the OS (Mach) first sends a
> message to the exception port of the current thread, then a message to the
> exception port of the process, and that's it. You need to catch these message.
> libsigsegv does that. gdb does that as well.
>
> Bruno
>
>
>
>

-- 
Camm Maguire                                        address@hidden
==========================================================================
"The earth is but one country, and mankind its citizens."  --  Baha'u'llah