Disable -Wdiv-by-zero for some tests in stdio-common/tst-unlockedio.c

[Joseph Myers <joseph at codesourcery dot com>]

This patch, relative to a tree with
<https://sourceware.org/ml/libc-alpha/2014-11/msg00736.html> (pending
review) applied, uses diagnostic control pragmas to disable some
division-by-zero warnings in stdio-common/tst-unlockedio.c.  This is
another test where disabling warnings using diagnostic pragmas seems
appropriate (the warnings are not wildly inappropriate for what the
test deliberately does; the deliberate use of unusual arguments to the
macros being tested means that changing the arguments in a way that
avoids the warning would also unduly perturb what is being tested).

Tested for x86_64.

2014-11-26  Joseph Myers  <joseph@codesourcery.com>

	* stdio-common/tst-unlockedio.c: Include <libc-internal.h>.
	(do_test): Disable -Wdiv-by-zero around some calls to
	fwrite_unlocked and fread_unlocked.

diff --git a/stdio-common/tst-unlockedio.c b/stdio-common/tst-unlockedio.c
index 4d17a4c..e557b59 100644
--- a/stdio-common/tst-unlockedio.c
+++ b/stdio-common/tst-unlockedio.c
@@ -20,6 +20,7 @@
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
+#include <libc-internal.h>
 
 int fd;
 static void do_prepare (void);
@@ -44,6 +45,13 @@ do_test (void)
 
   f = fp;
   cp = blah;
+  /* These tests deliberately use fwrite_unlocked with the size
+     argument specified as 0, which results in "division by zero"
+     warnings from the expansion of that macro (in code that is not
+     evaluated for a size of 0).  This applies to the tests of
+     fread_unlocked below as well.  */
+  DIAG_PUSH_NEEDS_COMMENT;
+  DIAG_IGNORE_NEEDS_COMMENT (4.9, "-Wdiv-by-zero");
   if (ftello (fp) != 0
       || fwrite_unlocked (blah, blah - blah, strlen (blah), f++) != 0
       || f != fp + 1
@@ -59,6 +67,7 @@ do_test (void)
       puts ("One of fwrite_unlocked tests failed");
       exit (1);
     }
+  DIAG_POP_NEEDS_COMMENT;
 
   if (fwrite_unlocked (blah, 1, strlen (blah) - 2, fp) != strlen (blah) - 2)
     {
@@ -93,6 +102,9 @@ do_test (void)
   f = fp;
   wp = buf;
   memset (buf, ' ', sizeof (buf));
+  /* See explanation above.  */
+  DIAG_PUSH_NEEDS_COMMENT;
+  DIAG_IGNORE_NEEDS_COMMENT (4.9, "-Wdiv-by-zero");
   if (ftello (fp) != 0
       || fread_unlocked (buf, buf - buf, strlen (blah), f++) != 0
       || f != fp + 1
@@ -109,6 +121,7 @@ do_test (void)
       puts ("One of fread_unlocked tests failed");
       exit (1);
     }
+  DIAG_POP_NEEDS_COMMENT;
 
   if (fread_unlocked (buf, 1, strlen (blah) - 2, fp) != strlen (blah) - 2)
     {

-- 
Joseph S. Myers
joseph@codesourcery.com