[2.25 COMMITTED] hppa: Fix guard alignment in allocate_stack when stack grows up.

[John David Anglin <dave.anglin@bell.net>]

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Back port of commit 075385f98af239ff5807a5c6ed17fec51e048454.

Dave
--
John David Anglin	dave.anglin@bell.net



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2017-08-12  John David Anglin  <danglin@gcc.gnu.org>

	* nptl/allocatestack.c (allocate_stack): Align old and new guard
	addresses to page boundaries when the stack grows up.

diff --git a/nptl/allocatestack.c b/nptl/allocatestack.c
index 8a228ab254..368fe3c36b 100644
--- a/nptl/allocatestack.c
+++ b/nptl/allocatestack.c
@@ -683,8 +683,14 @@ allocate_stack (const struct pthread_attr *attr, struct pthread **pdp,
 			prot) != 0)
 	    goto mprot_error;
 #elif _STACK_GROWS_UP
-	  if (mprotect ((char *) pd - pd->guardsize,
-			pd->guardsize - guardsize, prot) != 0)
+	  char *new_guard = (char *)(((uintptr_t) pd - guardsize)
+				     & ~pagesize_m1);
+	  char *old_guard = (char *)(((uintptr_t) pd - pd->guardsize)
+				     & ~pagesize_m1);
+	  /* The guard size difference might be > 0, but once rounded
+	     to the nearest page the size difference might be zero.  */
+	  if (new_guard > old_guard
+	      && mprotect (old_guard, new_guard - old_guard, prot) != 0)
 	    goto mprot_error;
 #endif