Re: [?] Find the address of a segfault in userland

Jason Duerstock (
Sat, 28 Feb 1998 13:19:05 -0500 (EST)

On 28 Feb 1998, David Mentre wrote:

> Hi all kernel hackers,
> Here is a problem I did not succeed to solve, even if I tried my best:
> ;)
> How can I have the faulting address of a SIGSEGV, from _userland_ ?
> My config: Linux 2.0.31 i686 SMP
> In fact, I try to do my own memory managment (with mmap() and
> mprotect() syscalls) in user area. I have made a SIGSEGV handler which
> is triggered on read/write protection faults. But how can I find the
> faulting address (to take the proper action with the faulting page
> number) ?
> I have looked at the kernel source and found[1] that the cr2 register
> (which contains my precious address ;) seems to be saved somewhere in
> the user stack. Unfortunatly, I've been unable to find this value in the
> segfault handler. Is it possible at all ? Should I use/calculate a
> specific offset from the stack pointer ? I must admit I'm completly lost
> in kernel's user process stack managment.
> Related question: in the 2.1.x saga, how to do the same thing ?
> Any help would be greatly appreciated,
> Regards,
> d.
> [1] arch/i386/kernel/signal.c:setup_frame()

#include <signal.h>
#include <sigcontext.h>

signal(SIGSEGV, sigsegv_handler);

void sigsegv_handler(int num, struct sigcontext info)
/* ignore the compiler whinings :D */
printf("EIP: %x\n", info.eip);

Not the world's greatest example, but hopefully enough to get the point
across. :)

Let me know if you need more info.


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