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authorDaniel Santos <daniel.santos@pobox.com>2013-02-21 16:41:55 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2013-02-21 17:22:16 -0800
commit9a8ab1c39970a4938a72d94e6fd13be88a797590 (patch)
treee95f9f02d7000dc6a79f5374f9adf6c85f936ad7 /include/linux/compiler.h
parentc361d3e54364d19bb5e803d6e766e94674da7b0e (diff)
downloadlwn-9a8ab1c39970a4938a72d94e6fd13be88a797590.tar.gz
lwn-9a8ab1c39970a4938a72d94e6fd13be88a797590.zip
bug.h, compiler.h: introduce compiletime_assert & BUILD_BUG_ON_MSG
Introduce compiletime_assert to compiler.h, which moves the details of how to break a build and emit an error message for a specific compiler to the headers where these details should be. Following in the tradition of the POSIX assert macro, compiletime_assert creates a build-time error when the supplied condition is *false*. Next, we add BUILD_BUG_ON_MSG to bug.h which simply wraps compiletime_assert, inverting the logic, so that it fails when the condition is *true*, consistent with the language "build bug on." This macro allows you to specify the error message you want emitted when the supplied condition is true. Finally, we remove all other code from bug.h that mucks with these details (BUILD_BUG & BUILD_BUG_ON), and have them all call BUILD_BUG_ON_MSG. This not only reduces source code bloat, but also prevents the possibility of code being changed for one macro and not for the other (which was previously the case for BUILD_BUG and BUILD_BUG_ON). Since __compiletime_error_fallback is now only used in compiler.h, I'm considering it a private macro and removing the double negation that's now extraneous. [akpm@linux-foundation.org: checkpatch fixes] Signed-off-by: Daniel Santos <daniel.santos@pobox.com> Cc: Andi Kleen <ak@linux.intel.com> Cc: Borislav Petkov <bp@alien8.de> Cc: David Rientjes <rientjes@google.com> Cc: Joe Perches <joe@perches.com> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux/compiler.h')
-rw-r--r--include/linux/compiler.h26
1 files changed, 25 insertions, 1 deletions
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 423bb6bd660f..10b8f23fab0f 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -308,11 +308,35 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
#ifndef __compiletime_error
# define __compiletime_error(message)
# define __compiletime_error_fallback(condition) \
- do { ((void)sizeof(char[1 - 2*!!(condition)])); } while (0)
+ do { ((void)sizeof(char[1 - 2 * condition])); } while (0)
#else
# define __compiletime_error_fallback(condition) do { } while (0)
#endif
+#define __compiletime_assert(condition, msg, prefix, suffix) \
+ do { \
+ bool __cond = !(condition); \
+ extern void prefix ## suffix(void) __compiletime_error(msg); \
+ if (__cond) \
+ prefix ## suffix(); \
+ __compiletime_error_fallback(__cond); \
+ } while (0)
+
+#define _compiletime_assert(condition, msg, prefix, suffix) \
+ __compiletime_assert(condition, msg, prefix, suffix)
+
+/**
+ * compiletime_assert - break build and emit msg if condition is false
+ * @condition: a compile-time constant condition to check
+ * @msg: a message to emit if condition is false
+ *
+ * In tradition of POSIX assert, this macro will break the build if the
+ * supplied condition is *false*, emitting the supplied error message if the
+ * compiler has support to do so.
+ */
+#define compiletime_assert(condition, msg) \
+ _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
+
/*
* Prevent the compiler from merging or refetching accesses. The compiler
* is also forbidden from reordering successive instances of ACCESS_ONCE(),