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.

(cherry picked from commit 3ecd616cc1782210d09c9678ec1a48899f19145b)

1 files changed, 57 insertions, 0 deletions

diff --git a/string/tester.c b/string/tester.c
index 7c36591d8d..25ffec9b36 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)
 		{