nptl: Use uintptr_t for address diagnostic in nptl/tst-pthread-getattr

Recent GCC versions warn about the attempt to return the address of a
local variable:

tst-pthread-getattr.c: In function ‘allocate_and_test’:
tst-pthread-getattr.c:54:10: error: function returns address of local variable [-Werror=return-local-addr]
   54 |   return mem;
      |          ^~~
In file included from ../include/alloca.h:3,
                 from tst-pthread-getattr.c:26:
../stdlib/alloca.h:35:23: note: declared here
   35 | # define alloca(size) __builtin_alloca (size)
      |                       ^~~~~~~~~~~~~~~~~~~~~~~
tst-pthread-getattr.c:51:9: note: in expansion of macro ‘alloca’
   51 |   mem = alloca ((size_t) (mem - target));
      |         ^~~~~~

The address itself is used in a check in the caller, so using
uintptr_t instead is reasonable.

2 files changed, 15 insertions, 8 deletions

diff --git a/ChangeLog b/ChangeLog
index 6099d1468a..a5384542a8 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2019-07-30  Florian Weimer  <fweimer@redhat.com>
+
+	* nptl/tst-pthread-getattr.c (allocate_and_test): Change return
+	type to uintptr_t.  Update comment.
+	(check_stack_top): Adjust.
+
 2019-07-29  Florian Weimer  <fweimer@redhat.com>
 
 	Linux: Move declaration of getdents64 to <dirent.h>.
diff --git a/nptl/tst-pthread-getattr.c b/nptl/tst-pthread-getattr.c
index a954778767..c13795c4bd 100644
--- a/nptl/tst-pthread-getattr.c
+++ b/nptl/tst-pthread-getattr.c
@@ -41,9 +41,11 @@
 
 static size_t pagesize;
 
-/* Check if the page in which TARGET lies is accessible.  This will segfault
-   if it fails.  */
-static volatile char *
+/* Test that the page in which TARGET lies is accessible.  This will
+   segfault if the write fails.  This function has only half a page
+   of thread stack left and so should not do anything and immediately
+   return the address to which the stack reached.  */
+static volatile uintptr_t
 allocate_and_test (char *target)
 {
   volatile char *mem = (char *) &mem;
@@ -51,7 +53,7 @@ allocate_and_test (char *target)
   mem = alloca ((size_t) (mem - target));
 
   *mem = 42;
-  return mem;
+  return (uintptr_t) mem;
 }
 
 static int
@@ -84,7 +86,6 @@ check_stack_top (void)
 {
   struct rlimit stack_limit;
   void *stackaddr;
-  volatile void *mem;
   size_t stacksize = 0;
   int ret;
   uintptr_t pagemask = ~(pagesize - 1);
@@ -130,14 +131,14 @@ check_stack_top (void)
      stack and test access there.  It is however sufficient to simply check if
      the top page is accessible, so we target our access halfway up the top
      page.  Thanks Chris Metcalf for this idea.  */
-  mem = allocate_and_test (stackaddr + pagesize / 2);
+  uintptr_t mem = allocate_and_test (stackaddr + pagesize / 2);
 
   /* Before we celebrate, make sure we actually did test the same page.  */
-  if (((uintptr_t) stackaddr & pagemask) != ((uintptr_t) mem & pagemask))
+  if (((uintptr_t) stackaddr & pagemask) != (mem & pagemask))
     {
       printf ("We successfully wrote into the wrong page.\n"
 	      "Expected %#" PRIxPTR ", but got %#" PRIxPTR "\n",
-	      (uintptr_t) stackaddr & pagemask, (uintptr_t) mem & pagemask);
+	      (uintptr_t) stackaddr & pagemask, mem & pagemask);
 
       return 1;
     }