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Add macros for diagnostic control, use for scanf %a tests.

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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.
This commit is contained in:
Joseph Myers
2014-12-10 00:41:19 +00:00
parent df7ecc6bd2
commit 2084e7ca4d
4 changed files with 73 additions and 0 deletions
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31
include/libc-internal.h
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@ -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 */