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| author | David Daney <david.daney@cavium.com> | 2012-01-10 15:07:25 -0800 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2015-05-09 23:16:12 +0100 |
| commit | 693c24191a7fec64311458b21ce0126d99059606 (patch) | |
| tree | 91448786186dc8dd93f3e32bbcdf9af78e7f5f76 /include/linux | |
| parent | cbeb30c62f1b5c9ec18840cbda54da4e33ed34b4 (diff) | |
| download | lwn-693c24191a7fec64311458b21ce0126d99059606.tar.gz lwn-693c24191a7fec64311458b21ce0126d99059606.zip | |
kernel.h: add BUILD_BUG() macro
commit 1399ff86f2a2bbacbbe68fa00c5f8c752b344723 upstream.
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>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/compiler-gcc4.h | 2 | ||||
| -rw-r--r-- | include/linux/compiler.h | 4 | ||||
| -rw-r--r-- | include/linux/kernel.h | 16 |
3 files changed, 21 insertions, 1 deletions
diff --git a/include/linux/compiler-gcc4.h b/include/linux/compiler-gcc4.h index e2a360ad6108..59a7e4cd9d7b 100644 --- a/include/linux/compiler-gcc4.h +++ b/include/linux/compiler-gcc4.h @@ -29,6 +29,8 @@ the kernel context */ #define __cold __attribute__((__cold__)) +#define __linktime_error(message) __attribute__((__error__(message))) + /* * GCC 'asm goto' miscompiles certain code sequences: * diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 7c7546bf1c10..65c8b78fc9af 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -297,7 +297,9 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect); #ifndef __compiletime_error # define __compiletime_error(message) #endif - +#ifndef __linktime_error +# define __linktime_error(message) +#endif /* * Prevent the compiler from merging or refetching accesses. The compiler * is also forbidden from reordering successive instances of ACCESS_ONCE(), diff --git a/include/linux/kernel.h b/include/linux/kernel.h index 0b8ca35595c9..dcf6a8b6412b 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -679,6 +679,7 @@ 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 */ @@ -717,6 +718,21 @@ 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 */ |