lkml.org 
[lkml]   [2003]   [Oct]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [x86] Access off the bottom of stack causes a segfault?
Chris Lattner wrote:

>My compiler is generating accesses off the bottom of the stack (address
>below %esp). Is there some funny kernel interaction that I should be
>aware of with this? I'm periodically getting segfaults.
>
>Example:
>
>int main() {
> int test[4000];
>...
> return 0;
>}
>
>Generated code:
> .intel_syntax
>...
>main:
> mov DWORD PTR [%ESP - 16004], %EBP # Save EBP to stack
> mov %EBP, %ESP # Set up EBP
> sub %ESP, 16004 # Finally adjust ESP
> lea %EAX, DWORD PTR [%EBP - 16000] # Get the address of the array
>...
> mov %EAX, 0 # Setup return value
> mov %ESP, %EBP # restore ESP
> mov %EBP, DWORD PTR [%ESP - 16004] # Restore EBP from stack
> ret
>
>This seems like perfectly valid X86 code (though unconventional), but it
>is causing segfaults pretty consistently (on the first instruction).
>Does the linux kernel assume that page faults will be above the stack
>pointer if the stack needs to be expanded?
>
>Thanks,
>
>-Chris
>
>
>
From arch/i386/mm/fault.c:
/*
* accessing the stack below %esp is always a bug.
* The "+ 32" is there due to some instructions (like
* pusha) doing post-decrement on the stack and that
* doesn't show up until later..
*/
if (address + 32 < regs->esp)
goto bad_area;
--
Brian Gerst

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:49    [from the cache]
©2003-2011 Jasper Spaans. Advertise on this site