Re: tst-pthread-getattr changes break sparc

[Siddhesh Poyarekar <siddhesh at redhat dot com>]

On Wed, 25 Jul 2012 00:16:26 -0700 (PDT), David wrote:
> > Do you want me to disable the test case till I fix this?
> 
> You added a regression, so a revert would be more appropriate.

Right, that is what the consensus document says, but I thought it would
be better in this case to disable the test case instead, since
reverting the fix either breaks the test case on x86 (albeit
sporadically) or is useless since its key code is optimized out.

The patch for the revert is attached if that is seen as necessary in
this case.

Regards,
Siddhesh

2012-07-25  Siddhesh Poyarekar  <siddhesh@redhat.com>

        * tst-pthread-getattr.c: Revert last change.

diff --git a/nptl/tst-pthread-getattr.c b/nptl/tst-pthread-getattr.c
index 692bce4..6f2cfc6 100644
--- a/nptl/tst-pthread-getattr.c
+++ b/nptl/tst-pthread-getattr.c
@@ -23,38 +23,16 @@
 #include <sys/resource.h>
 #include <pthread.h>
 #include <alloca.h>
-#include <assert.h>
-
-/* There is an obscure bug in the kernel due to which RLIMIT_STACK is sometimes
-   returned as unlimited when it is not, which may cause this test to fail.
-   There is also the other case where RLIMIT_STACK is intentionally set as
-   unlimited or very high, which may result in a vma that is too large and again
-   results in a test case failure.  To avoid these problems, we cap the stack
-   size to one less than 8M.  See the following mailing list threads for more
-   information about this problem:
-   <http://sourceware.org/ml/libc-alpha/2012-06/msg00599.html>
-   <http://sourceware.org/ml/libc-alpha/2012-06/msg00713.html>.  */
-#define MAX_STACK_SIZE (8192 * 1024 - 1)
-
-#define _MIN(l,o) ((l) < (o) ? (l) : (o))
 
 /* Move the stack pointer so that stackaddr is accessible and then check if it
    really is accessible.  This will segfault if it fails.  */
-static void *
+static void
 allocate_and_test (void *stackaddr)
 {
   void *mem = &mem;
-  /* FIXME:  mem >= stackaddr for _STACK_GROWSUP.  */
+  /* FIXME:  The difference will be negative for _STACK_GROWSUP.  */
   mem = alloca ((size_t) (mem - stackaddr));
-  assert (mem <= stackaddr);
-
-  /* We don't access mem here because the compiler may move the stack pointer
-     beyond what we expect, thus making our alloca send the stack pointer
-     beyond stackaddr.  Using only stackaddr without the assert may make the
-     compiler think that this instruction is independent of the above alloca
-     and hence reshuffle to do this dereference before the alloca.  */
-  *(int *)stackaddr = 42;
-  return stackaddr;
+  *(int *)(mem) = 0;
 }
 
 static int
@@ -99,20 +77,17 @@ check_stack_top (void)
       return 1;
     }
 
-  printf ("current rlimit_stack is %zu\n", stack_limit.rlim_cur);
-
   if (get_self_pthread_attr ("check_stack_top", &stackaddr, &stacksize))
     return 1;
 
-  /* Reduce the rlimit to a page less that what is currently being returned
-     (subject to a maximum of MAX_STACK_SIZE) so that we ensure that
-     pthread_getattr_np uses rlimit.  The figure is intentionally unaligned so
-     to verify that pthread_getattr_np returns an aligned stacksize that
-     correctly fits into the rlimit.  We don't bother about the case where the
-     stack is limited by the vma below it and not by the rlimit because the
-     stacksize returned in that case is computed from the end of that vma and is
-     hence safe.  */
-  stack_limit.rlim_cur = _MIN(stacksize - 4095, MAX_STACK_SIZE);
+  /* Reduce the rlimit to a page less that what is currently being returned so
+     that we ensure that pthread_getattr_np uses rlimit.  The figure is
+     intentionally unaligned so to verify that pthread_getattr_np returns an
+     aligned stacksize that correctly fits into the rlimit.  We don't bother
+     about the case where the stack is limited by the vma below it and not by
+     the rlimit because the stacksize returned in that case is computed from
+     the end of that vma and is hence safe.  */
+  stack_limit.rlim_cur = stacksize - 4095;
   printf ("Adjusting RLIMIT_STACK to %zu\n", stack_limit.rlim_cur);
   if ((ret = setrlimit (RLIMIT_STACK, &stack_limit)))
     {
@@ -125,10 +100,7 @@ check_stack_top (void)
 
   printf ("Adjusted rlimit: stacksize=%zu, stackaddr=%p\n", stacksize,
           stackaddr);
-
-  /* So that the compiler does not optimize out this call.  */
-  stackaddr = allocate_and_test (stackaddr);
-  assert (*(int *)stackaddr == 42);
+  allocate_and_test (stackaddr);
 
   puts ("Stack top tests done");