The patch titled
Subject: compiler.h, bug.h: Prevent double error messages with BUILD_BUG{,_ON}
has been added to the -mm tree. Its filename is
compilerh-bugh-prevent-double-error-messages-with-build_bug_on.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Daniel Santos <daniel.santos@xxxxxxxxx>
Subject: compiler.h, bug.h: Prevent double error messages with BUILD_BUG{,_ON}
Prior to the introduction of __attribute__((error("msg"))) in gcc 4.3,
creating compile-time errors required a little trickery. BUILD_BUG{,_ON}
uses this attribute when available to generate compile-time errors, but
also uses the negative-sized array trick for older compilers, resulting in
two error messages in some cases. The reason it's "some" cases is that as
of gcc 4.4, the negative-sized array will not create an error in some
situations, like inline functions.
This patch replaces the negative-sized array code with the new
__compiletime_error_fallback() macro which expands to the same thing
unless the the error attribute is available, in which case it expands to
do{}while(0), resulting in exactly one compile-time error on all versions
of gcc.
Note that we are not changing the negative-sized array code for the
unoptimized version of BUILD_BUG_ON, since it has the potential to catch
problems that would be disabled in later versions of gcc were
__compiletime_error_fallback used. The reason is that that an unoptimized
build can't always remove calls to an error-attributed function call (like
we are using) that should effectively become dead code if it were
optimized. However, using a negative-sized array with a similar value
will not result in an false-positive (error). The only caveat being that
it will also fail to catch valid conditions, which we should be expecting
in an unoptimized build anyway.
Signed-off-by: Daniel Santos <daniel.santos@xxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joe Perches <joe@xxxxxxxxxxx>
Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Cc: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/bug.h | 2 +-
include/linux/compiler.h | 5 +++++
2 files changed, 6 insertions(+), 1 deletion(-)
diff -puN include/linux/bug.h~compilerh-bugh-prevent-double-error-messages-with-build_bug_on include/linux/bug.h
--- a/include/linux/bug.h~compilerh-bugh-prevent-double-error-messages-with-build_bug_on
+++ a/include/linux/bug.h
@@ -67,7 +67,7 @@ struct pt_regs;
__compiletime_error("BUILD_BUG_ON failed"); \
if (__cond) \
__build_bug_on_failed(); \
- ((void)sizeof(char[1 - 2 * __cond])); \
+ __compiletime_error_fallback(__cond); \
} while(0)
#endif
diff -puN include/linux/compiler.h~compilerh-bugh-prevent-double-error-messages-with-build_bug_on include/linux/compiler.h
--- a/include/linux/compiler.h~compilerh-bugh-prevent-double-error-messages-with-build_bug_on
+++ a/include/linux/compiler.h
@@ -307,7 +307,12 @@ void ftrace_likely_update(struct ftrace_
#endif
#ifndef __compiletime_error
# define __compiletime_error(message)
+# define __compiletime_error_fallback(condition) \
+ do { ((void)sizeof(char[1 - 2*!!(condition)])); } while (0)
+#else
+# define __compiletime_error_fallback(condition) do { } while (0)
#endif
+
/*
* Prevent the compiler from merging or refetching accesses. The compiler
* is also forbidden from reordering successive instances of ACCESS_ONCE(),
_
Patches currently in -mm which might be from daniel.santos@xxxxxxxxx are
compiler-gcc4h-reorder-macros-based-upon-gcc-ver.patch
compiler-gcch-add-gcc-recommended-gcc_version-macro.patch
compiler-gcc34h-use-gcc_version-macro.patch
compiler-gcc4h-bugh-remove-duplicate-macros.patch
bugh-fix-build_bug_on-macro-in-__checker__.patch
bugh-prevent-double-evaulation-of-in-build_bug_on.patch
bugh-make-build_bug_on-generate-compile-time-error.patch
compilerh-bugh-prevent-double-error-messages-with-build_bug_on.patch
bugh-compilerh-introduce-compiletime_assert-build_bug_on_msg.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
