Re: [Valgrind-users] not understanding some valgrind errors against afs...

[Thomas R. T. <tr...@cs...>]

valgrind seems to have a problem with swapcontext() tasking.
We use getcontext/setcontext/swapcontext
rather than setjmp/longjmp for tasking.
The *context routines are slower than *jmp
but seem to be a more official API for tasking.

For example the program below triggers messages such as:
==26015== Invalid write of size 4
==26015==    at 0x42045D6C: __swapcontext (in /lib/i686/libc-2.2.93.so)
==26015==    Address 0xBFFFE9BC is on thread 1's stack

This isn't a problem for us, since we can optionally use pthread tasking.
But I thought I should mention it.

Tom Truscott

#include <stdio.h>
#include <stdlib.h>
#include <ucontext.h>

ucontext_t  child, parent;

#define STACKSZ (256*1024)

void childfunc(void)
{
   printf("entering child\n");

   swapcontext(&child, &parent);

   printf("leaving child\n");
}

int
main()
{
   printf("entering main\n");

   getcontext(&child);
   child.uc_link = 0;
   child.uc_stack.ss_sp = malloc(STACKSZ);
   child.uc_stack.ss_size = STACKSZ;
   child.uc_stack.ss_flags = 0;
   makecontext(&child, (void(*)())childfunc, 0);

   swapcontext(&parent, &child);

   printf("leaving main\n");

   return 0;
}