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authorDavid Daney <david.daney@cavium.com>2012-01-10 15:07:25 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2012-01-10 16:30:42 -0800
commit1399ff86f2a2bbacbbe68fa00c5f8c752b344723 (patch)
tree7cfb8e346ff8d750cbf33bb0655603e21e394c37 /include/linux/kernel.h
parent1e16a539ac16e7b3a8c2cee188897d4bdb88e6e8 (diff)
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kernel.h: add BUILD_BUG() macro
We can place this in definitions that we expect the compiler to remove by dead code elimination. If this assertion fails, we get a nice error message at build time. The GCC function attribute error("message") was added in version 4.3, so we define a new macro __linktime_error(message) to expand to this for GCC-4.3 and later. This will give us an error diagnostic from the compiler on the line that fails. For other compilers __linktime_error(message) expands to nothing, and we have to be content with a link time error, but at least we will still get a build error. BUILD_BUG() expands to the undefined function __build_bug_failed() and will fail at link time if the compiler ever emits code for it. On GCC-4.3 and later, attribute((error())) is used so that the failure will be noted at compile time instead. Signed-off-by: David Daney <david.daney@cavium.com> Acked-by: David Rientjes <rientjes@google.com> Cc: DM <dm.n9107@gmail.com> Cc: Ralf Baechle <ralf@linux-mips.org> Acked-by: David Howells <dhowells@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux/kernel.h')
-rw-r--r--include/linux/kernel.h16
1 files changed, 16 insertions, 0 deletions
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index e8b1597b5cf2..f48e8a528544 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -665,6 +665,7 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { }
#define BUILD_BUG_ON_ZERO(e) (0)
#define BUILD_BUG_ON_NULL(e) ((void*)0)
#define BUILD_BUG_ON(condition)
+#define BUILD_BUG() (0)
#else /* __CHECKER__ */
/* Force a compilation error if a constant expression is not a power of 2 */
@@ -703,6 +704,21 @@ extern int __build_bug_on_failed;
if (condition) __build_bug_on_failed = 1; \
} while(0)
#endif
+
+/**
+ * BUILD_BUG - break compile if used.
+ *
+ * If you have some code that you expect the compiler to eliminate at
+ * build time, you should use BUILD_BUG to detect if it is
+ * unexpectedly used.
+ */
+#define BUILD_BUG() \
+ do { \
+ extern void __build_bug_failed(void) \
+ __linktime_error("BUILD_BUG failed"); \
+ __build_bug_failed(); \
+ } while (0)
+
#endif /* __CHECKER__ */
/* Trap pasters of __FUNCTION__ at compile-time */
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