commit 2084e7ca4d344c39eb39e53848b51b5d84444414
Author: Joseph Myers <joseph@codesourcery.com>
Date: Wed Dec 10 00:41:19 2014 +0000
Add macros for diagnostic control, use for scanf %a tests.
In <https://sourceware.org/ml/libc-alpha/2014-11/msg00326.html>,
Roland requested internal macros for use of "#pragma GCC diagnostic".
This patch adds such macros and uses them to disable -Wformat warnings
for some code testing GNU scanf %as where GCC expects C99 scanf %a
(several other stdio tests currently use -Wno-format to disable
warnings). Limitations in GCC's diagnostic pragmas require separate
macros before and after the code generating the warnings, rather than
a single macro taking that code as an argument.
The macros are named DIAG_*_NEEDS_COMMENT to emphasise to reviewers
the need for a comment accompanying any use of them (such comments may
however just appear once for several uses of the macros for the same
issue in the same file). I put a GCC version in the arguments to
DIAG_IGNORE_NEEDS_COMMENT, as that seems something useful to grep for
when obsoleting support for an old GCC version and needing to decide
if warning-disabling code is still relevant.
These macros should be usable for replacing existing -Wno-* use in
makefiles (as also suggested by Roland), though I have no plans to
work on that (only on use of the macros in cases where warnings are
currently present that need disabling to use -Werror).
Tested for x86_64.
* include/libc-internal.h (DIAG_PUSH_NEEDS_COMMENT): New macro.
(DIAG_POP_NEEDS_COMMENT): Likewise.
(_DIAG_STR1): Likewise.
(_DIAG_STR): Likewise.
(DIAG_IGNORE_NEEDS_COMMENT): Likewise.
* stdio-common/bug21.c: Include <libc-internal.h>.
(do_test): Disable -Wformat around call to sscanf.
* stdio-common/scanf14.c: Include <libc-internal.h>.
(main): Disable -Wformat around some calls to scanf functions.
diff --git a/include/libc-internal.h b/include/libc-internal.h
index 2ced1c17d3dff93d..bca59a46144b736f 100644
--- a/include/libc-internal.h
+++ b/include/libc-internal.h
@@ -76,4 +76,35 @@ extern void __init_misc (int, char **, char **);
#define ignore_value(x) \
({ __typeof__ (x) __ignored_value = (x); (void) __ignored_value; })
+/* The macros to control diagnostics are structured like this, rather
+ than a single macro that both pushes and pops diagnostic state and
+ takes the affected code as an argument, because the GCC pragmas
+ work by disabling the diagnostic for a range of source locations
+ and do not work when all the pragmas and the affected code are in a
+ single macro expansion. */
+
+/* Push diagnostic state. */
+#define DIAG_PUSH_NEEDS_COMMENT _Pragma ("GCC diagnostic push")
+
+/* Pop diagnostic state. */
+#define DIAG_POP_NEEDS_COMMENT _Pragma ("GCC diagnostic pop")
+
+#define _DIAG_STR1(s) #s
+#define _DIAG_STR(s) _DIAG_STR1(s)
+
+/* Ignore the diagnostic OPTION. VERSION is the most recent GCC
+ version for which the diagnostic has been confirmed to appear in
+ the absence of the pragma (in the form MAJOR.MINOR for GCC 4.x,
+ just MAJOR for GCC 5 and later). Uses of this pragma should be
+ reviewed when the GCC version given is no longer supported for
+ building glibc; the version number should always be on the same
+ source line as the macro name, so such uses can be found with grep.
+ Uses should come with a comment giving more details of the
+ diagnostic, and an architecture on which it is seen if possibly
+ optimization-related and not in architecture-specific code. This
+ macro should only be used if the diagnostic seems hard to fix (for
+ example, optimization-related false positives). */
+#define DIAG_IGNORE_NEEDS_COMMENT(version, option) \
+ _Pragma (_DIAG_STR (GCC diagnostic ignored option))
+
#endif /* _LIBC_INTERNAL */
diff --git a/stdio-common/bug21.c b/stdio-common/bug21.c
index d22b9c1a9717a197..ca27272ba191321e 100644
--- a/stdio-common/bug21.c
+++ b/stdio-common/bug21.c
@@ -1,4 +1,5 @@
#include <stdio.h>
+#include <libc-internal.h>
static int
do_test (void)
@@ -6,7 +7,15 @@ do_test (void)
static const char buf[] = " ";
char *str;
+ /* GCC in C99 mode treats %a as the C99 format expecting float *,
+ but glibc with _GNU_SOURCE treats %as as the GNU allocation
+ extension, so resulting in "warning: format '%a' expects argument
+ of type 'float *', but argument 3 has type 'char **'". This
+ applies to the other %as, %aS and %a[] formats below as well. */
+ DIAG_PUSH_NEEDS_COMMENT;
+ DIAG_IGNORE_NEEDS_COMMENT (4.9, "-Wformat");
int r = sscanf (buf, "%as", &str);
+ DIAG_POP_NEEDS_COMMENT;
printf ("%d %p\n", r, str);
return r != -1 || str != NULL;
diff --git a/stdio-common/scanf14.c b/stdio-common/scanf14.c
index 6ca5c7c5679632a3..cffccb0b19d2927b 100644
--- a/stdio-common/scanf14.c
+++ b/stdio-common/scanf14.c
@@ -2,6 +2,7 @@
#include <stdlib.h>
#include <string.h>
#include <wchar.h>
+#include <libc-internal.h>
#define FAIL() \
do { \
@@ -23,6 +24,13 @@ main (void)
FAIL ();
else if (f != 0.25 || memcmp (c, "s x", 3) != 0)
FAIL ();
+ /* GCC in C99 mode treats %a as the C99 format expecting float *,
+ but glibc with _GNU_SOURCE treats %as as the GNU allocation
+ extension, so resulting in "warning: format '%a' expects argument
+ of type 'float *', but argument 3 has type 'char **'". This
+ applies to the other %as, %aS and %a[] formats below as well. */
+ DIAG_PUSH_NEEDS_COMMENT;
+ DIAG_IGNORE_NEEDS_COMMENT (4.9, "-Wformat");
if (sscanf (" 1.25s x", "%as%2c", &sp, c) != 2)
FAIL ();
else
@@ -32,10 +40,14 @@ main (void)
memset (sp, 'x', sizeof "1.25s");
free (sp);
}
+ DIAG_POP_NEEDS_COMMENT;
if (sscanf (" 2.25s x", "%las%2c", &d, c) != 2)
FAIL ();
else if (d != 2.25 || memcmp (c, " x", 2) != 0)
FAIL ();
+ /* See explanation above. */
+ DIAG_PUSH_NEEDS_COMMENT;
+ DIAG_IGNORE_NEEDS_COMMENT (4.9, "-Wformat");
if (sscanf (" 3.25S x", "%4aS%3c", &lsp, c) != 2)
FAIL ();
else
@@ -54,6 +66,7 @@ main (void)
memset (sp, 'x', sizeof "4.25");
free (sp);
}
+ DIAG_POP_NEEDS_COMMENT;
if (sscanf ("5.25[0-9.] x", "%la[0-9.]%2c", &d, c) != 2)
FAIL ();
else if (d != 5.25 || memcmp (c, " x", 2) != 0)
@@ -82,6 +95,9 @@ main (void)
FAIL ();
if (fseek (fp, 0, SEEK_SET) != 0)
FAIL ();
+ /* See explanation above. */
+ DIAG_PUSH_NEEDS_COMMENT;
+ DIAG_IGNORE_NEEDS_COMMENT (4.9, "-Wformat");
if (fscanf (fp, "%as%2c", &sp, c) != 2)
FAIL ();
else
@@ -91,11 +107,15 @@ main (void)
memset (sp, 'x', sizeof "1.25s");
free (sp);
}
+ DIAG_POP_NEEDS_COMMENT;
if (freopen (fname, "r", stdin) == NULL)
FAIL ();
else
{
+ /* See explanation above. */
+ DIAG_PUSH_NEEDS_COMMENT;
+ DIAG_IGNORE_NEEDS_COMMENT (4.9, "-Wformat");
if (scanf ("%as%2c", &sp, c) != 2)
FAIL ();
else
@@ -105,6 +125,7 @@ main (void)
memset (sp, 'x', sizeof "1.25s");
free (sp);
}
+ DIAG_POP_NEEDS_COMMENT;
}
fclose (fp);