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);