[Linux-ia64] linuxthread stack problem

[Philip Armstrong <pma@sgi.com>]

All,

I have run into a linuxthread problem that is caused by some (bad ?)
assumptions on stack address usage. The problem manifests itself in the
pthread_cleanup_push() and pthread_cleanup_pop() macros. The symptom of
the problem is that a pthread_cancel does not execute all of the
thread's cleanup routines if more than one routine gets pushed onto the
cleanup stack in the same subroutine.

The reason for the problem is that the pthread_cancel code that pops and
executes the cleanup 'stack' continues using the _prev value of each
pthread_cleanup frame until the stack address of the next frame is
greater|less than the current one based on a #define named either
STACK_GROWS_UP or STACK_GROWS_DOWN. I believe this is based on the
assumption that as you  progress down|up the stack by going into or
returning from subroutines, the stack does indeed grow down|up.

While in the same subroutine, however, the ordering of the
pthread_cleanup_buffer stack addresses as allocated by the
pthread_cleanup_push macro is indeterminate, at least it is on our IA64
platform.

I have simplified the problem into a short test case that uses the
bracketing and stack address allocation in the same manner that the
pthread_cleanup_push() and pthread_cleanup_pop() macros do. In my case,
we have STACK_GROW_DOWN defined, and as you can see the second stack
address is actually greater than the first. The pthread_cancel routine
would not execute the second cleanup subroutine put on the stack in this
case becuase the address comparison (FRAME_LEFT in
linuxthreads/cancel.c) would prohibit it.

I scanned the linux-ia64 archive for any discussion on this topic and
found none. I'm not sure if this problem is out there on any other IA64
platforms, either. I guess you can try the test case and see for
yourself.

Test program:

#include <stdio.h>
#include <malloc.h>

main(int argc, char **argv)
{
        printf("hello\n");
  {
    int x = 1;
    printf("x = %d, &x = %x\n", x, &x);

    {
      int y = 2;
      printf("y = %d, &y = %x\n", y, &y);
    }

  }
        printf("goodbye\n");

}

My results:

hello
x = 1, &x = ffffb4e0
y = 2, &y = ffffb4e4
goodbye


-- 
	Phil Armstrong       pma@sgi.com
	Phone: 651-683-5561  VNET 233-5561