Fix string/tester.c for GCC 7 -Wstringop-overflow=.

GCC 7 has a -Wstringop-overflow= warning that includes warning for
strncat with a size specified that is larger than the size of the
buffer (which is dubious usage, but valid at runtime if in fact there
isn't an overflow with the particular buffer contents present).
string/tester.c tests such cases; this patch arranges for this warning
to be ignored around relevant strncat calls.

Tested compilation for aarch64 (GCC mainline) with
build-many-glibcs.py; did execution testing for x86_64 (GCC 5).

	* string/tester.c (test_strncat): Disable -Wstringop-overflow=
	around tests of strncat with large sizes.

2 files changed, 60 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index a3eacbb604..df77ffa1c2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,8 @@
 2017-01-04  Joseph Myers  <joseph@codesourcery.com>
 
+	* string/tester.c (test_strncat): Disable -Wstringop-overflow=
+	around tests of strncat with large sizes.
+
 	* malloc/tst-malloc.c: Include <libc-internal.h>.
 	(do_test): Disable -Walloc-size-larger-than= around tests of
 	malloc with negative sizes.
diff --git a/string/tester.c b/string/tester.c
index 8b68537fa8..ec350243eb 100644
--- a/string/tester.c
+++ b/string/tester.c
@@ -353,28 +353,70 @@ test_strncat (void)
      mechanism.  */
   it = "strncat";
   (void) strcpy (one, "ijk");
+  DIAG_PUSH_NEEDS_COMMENT;
+#if __GNUC_PREREQ (7, 0)
+  /* GCC 7 warns about the size passed to strncat being larger than
+     the size of the buffer; this is deliberately tested here..  */
+  DIAG_IGNORE_NEEDS_COMMENT (7, "-Wstringop-overflow=");
+#endif
   check (strncat (one, "lmn", 99) == one, 1);	/* Returned value. */
+  DIAG_POP_NEEDS_COMMENT;
   equal (one, "ijklmn", 2);		/* Basic test. */
 
   (void) strcpy (one, "x");
+  DIAG_PUSH_NEEDS_COMMENT;
+#if __GNUC_PREREQ (7, 0)
+  /* GCC 7 warns about the size passed to strncat being larger than
+     the size of the buffer; this is deliberately tested here..  */
+  DIAG_IGNORE_NEEDS_COMMENT (7, "-Wstringop-overflow=");
+#endif
   (void) strncat (one, "yz", 99);
+  DIAG_POP_NEEDS_COMMENT;
   equal (one, "xyz", 3);		/* Writeover. */
   equal (one+4, "mn", 4);		/* Wrote too much? */
 
   (void) strcpy (one, "gh");
   (void) strcpy (two, "ef");
+  DIAG_PUSH_NEEDS_COMMENT;
+#if __GNUC_PREREQ (7, 0)
+  /* GCC 7 warns about the size passed to strncat being larger than
+     the size of the buffer; this is deliberately tested here..  */
+  DIAG_IGNORE_NEEDS_COMMENT (7, "-Wstringop-overflow=");
+#endif
   (void) strncat (one, two, 99);
+  DIAG_POP_NEEDS_COMMENT;
   equal (one, "ghef", 5);			/* Basic test encore. */
   equal (two, "ef", 6);			/* Stomped on source? */
 
   (void) strcpy (one, "");
+  DIAG_PUSH_NEEDS_COMMENT;
+#if __GNUC_PREREQ (7, 0)
+  /* GCC 7 warns about the size passed to strncat being larger than
+     the size of the buffer; this is deliberately tested here..  */
+  DIAG_IGNORE_NEEDS_COMMENT (7, "-Wstringop-overflow=");
+#endif
   (void) strncat (one, "", 99);
+  DIAG_POP_NEEDS_COMMENT;
   equal (one, "", 7);			/* Boundary conditions. */
   (void) strcpy (one, "ab");
+  DIAG_PUSH_NEEDS_COMMENT;
+#if __GNUC_PREREQ (7, 0)
+  /* GCC 7 warns about the size passed to strncat being larger than
+     the size of the buffer; this is deliberately tested here..  */
+  DIAG_IGNORE_NEEDS_COMMENT (7, "-Wstringop-overflow=");
+#endif
   (void) strncat (one, "", 99);
+  DIAG_POP_NEEDS_COMMENT;
   equal (one, "ab", 8);
   (void) strcpy (one, "");
+  DIAG_PUSH_NEEDS_COMMENT;
+#if __GNUC_PREREQ (7, 0)
+  /* GCC 7 warns about the size passed to strncat being larger than
+     the size of the buffer; this is deliberately tested here..  */
+  DIAG_IGNORE_NEEDS_COMMENT (7, "-Wstringop-overflow=");
+#endif
   (void) strncat (one, "cd", 99);
+  DIAG_POP_NEEDS_COMMENT;
   equal (one, "cd", 9);
 
   (void) strcpy (one, "ab");
@@ -387,7 +429,14 @@ test_strncat (void)
   (void) strncat (one, "gh", 2);
   equal (one, "abcdgh", 12);		/* Count and length equal. */
 
+  DIAG_PUSH_NEEDS_COMMENT;
+#if __GNUC_PREREQ (7, 0)
+  /* GCC 7 warns about the size passed to strncat being larger than
+     the size of the buffer; this is deliberately tested here..  */
+  DIAG_IGNORE_NEEDS_COMMENT (7, "-Wstringop-overflow=");
+#endif
   (void) strncat (one, "ij", (size_t)-1);	/* set sign bit in count */
+  DIAG_POP_NEEDS_COMMENT;
   equal (one, "abcdghij", 13);
 
   int ntest = 14;
@@ -406,8 +455,16 @@ test_strncat (void)
 	    buf1[n2 + n3] = '\0';
 	    strcpy (buf2 + n1, "123");
 
+	    DIAG_PUSH_NEEDS_COMMENT;
+#if __GNUC_PREREQ (7, 0)
+	    /* GCC 7 warns about the size passed to strncat being
+	       larger than the size of the buffer; this is
+	       deliberately tested here..  */
+	    DIAG_IGNORE_NEEDS_COMMENT (7, "-Wstringop-overflow=");
+#endif
 	    check (strncat (buf1 + n2, buf2 + n1, ~((size_t) 0) - n4)
 		   == buf1 + n2, ntest);
+	    DIAG_POP_NEEDS_COMMENT;
 	    if (errors == olderrors)
 	      for (size_t i = 0; i < sizeof (buf1); ++i)
 		{