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[PATCH v2] Fix stacksize returned for main process thread whenRLIMIT_STACK is relevant


Hi,

This is version 2 of the patch. I have removed the conditional that
Kosaki pointed out as unnecessary; everything else remains the same.

nptl/ChangeLog:

2012-06-15  Siddhesh Poyarekar  <siddhesh@redhat.com>

	* Makefile (tests): Add test case.
	* pthread_getattr_np.c (pthread_getattr_np): Deduct pages below
	the __libc_stack_end page from stacksize.  Truncate stacksize
	to make it page aligned when it is computed from RLIMIT_STACK.
	* tst-pthread-getattr.c: New test case. Verify that stackaddr
	is accessible.
diff --git a/nptl/Makefile b/nptl/Makefile
index 2a36d01..ef8e874 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -245,7 +245,7 @@ tests = tst-typesizes \
 	tst-exec1 tst-exec2 tst-exec3 tst-exec4 \
 	tst-exit1 tst-exit2 tst-exit3 \
 	tst-stdio1 tst-stdio2 \
-	tst-stack1 tst-stack2 tst-stack3 \
+	tst-stack1 tst-stack2 tst-stack3 tst-pthread-getattr \
 	tst-unload \
 	tst-dlsym1 \
 	tst-sysconf \
diff --git a/nptl/pthread_getattr_np.c b/nptl/pthread_getattr_np.c
index 75d717b..7309185 100644
--- a/nptl/pthread_getattr_np.c
+++ b/nptl/pthread_getattr_np.c
@@ -120,8 +120,15 @@ pthread_getattr_np (thread_id, attr)
 		      && (uintptr_t) __libc_stack_end < to)
 		    {
 		      /* Found the entry.  Now we have the info we need.  */
-		      iattr->stacksize = rl.rlim_cur;
 		      iattr->stackaddr = stack_end;
+		      iattr->stacksize =
+		        rl.rlim_cur - (size_t) (to - (uintptr_t) stack_end);
+
+		      /* Cut it down to align it to page size since otherwise we
+		         risk going beyond rlimit when the kernel rounds up the
+		         stack extension request.  */
+		      iattr->stacksize = (iattr->stacksize
+					  & -(intptr_t) GLRO(dl_pagesize));
 
 		      /* The limit might be too high.  */
 		      if ((size_t) iattr->stacksize
diff --git a/nptl/tst-pthread-getattr.c b/nptl/tst-pthread-getattr.c
new file mode 100644
index 0000000..82dd74c
--- /dev/null
+++ b/nptl/tst-pthread-getattr.c
@@ -0,0 +1,102 @@
+/* Make sure that the stackaddr returned by pthread_getattr_np is
+   reachable.  */
+
+#include <stdio.h>
+#include <string.h>
+#include <sys/resource.h>
+#include <pthread.h>
+#include <alloca.h>
+
+/* 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
+allocate_and_test (void *stackaddr)
+{
+  void *mem = &mem;
+  mem = alloca ((size_t) (mem - stackaddr));
+  *(int *)(mem) = 0;
+}
+
+static int
+get_self_pthread_attr (const char *id, void **stackaddr, size_t *stacksize)
+{
+  pthread_attr_t attr;
+  int ret;
+  pthread_t me = pthread_self ();
+
+  if ((ret = pthread_getattr_np (me, &attr)))
+    {
+      printf ("%s: pthread_getattr_np failed: %s\n", id, strerror (ret));
+      return 1;
+    }
+
+  if ((ret = pthread_attr_getstack (&attr, stackaddr, stacksize)))
+    {
+      printf ("%s: pthread_attr_getstack returned error: %s\n", id,
+	      strerror (ret));
+      return 1;
+    }
+
+  return 0;
+}
+
+/* Verify that the stack size returned by pthread_getattr_np is usable when
+   the returned value is subject to rlimit.  */
+static int
+check_stack_top (void)
+{
+  struct rlimit stack_limit;
+  void *stackaddr;
+  size_t stacksize = 0;
+  int ret;
+
+  puts ("Verifying that stack top is accessible");
+
+  ret = getrlimit (RLIMIT_STACK, &stack_limit);
+  if (ret)
+    {
+      perror ("getrlimit failed");
+      return 1;
+    }
+
+  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 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)))
+    {
+      perror ("setrlimit failed");
+      return 1;
+    }
+
+  if (get_self_pthread_attr ("check_stack_top2", &stackaddr, &stacksize))
+    return 1;
+
+  printf ("Adjusted rlimit: stacksize=%zu, stackaddr=%p\n", stacksize,
+          stackaddr);
+  allocate_and_test (stackaddr);
+
+  puts ("Stack top tests done");
+
+  return 0;
+}
+
+/* TODO: Similar check for thread stacks once the thread stack sizes are
+   fixed.  */
+static int
+do_test (void)
+{
+  return check_stack_top ();
+}
+
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"

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