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.

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>

diff --git a/include/linux/bug.h b/include/linux/bug.h
index dc11dc762fc34e55367bbec155f0c2ce2ef3a0cf..3c09a000b3357e678c6d7c399b703ca5f8eeb2e8 100644 (file)
--- a/include/linux/bug.h
+++ b/include/linux/bug.h
@@ -17,6 +17,7 @@ struct pt_regs;
 #define BUILD_BUG_ON_ZERO(e) (0)
 #define BUILD_BUG_ON_NULL(e) ((void*)0)
 #define BUILD_BUG_ON_INVALID(e) (0)
+#define BUILD_BUG_ON_MSG(cond, msg) (0)
 #define BUILD_BUG_ON(condition) (0)
 #define BUILD_BUG() (0)
 #else /* __CHECKER__ */
@@ -39,6 +40,15 @@ struct pt_regs;
  */
 #define BUILD_BUG_ON_INVALID(e) ((void)(sizeof((__force long)(e))))
 
+/**
+ * BUILD_BUG_ON_MSG - break compile if a condition is true & emit supplied
+ *                   error message.
+ * @condition: the condition which the compiler should know is false.
+ *
+ * See BUILD_BUG_ON for description.
+ */
+#define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
+
 /**
  * BUILD_BUG_ON - break compile if a condition is true.
  * @condition: the condition which the compiler should know is false.
@@ -60,15 +70,8 @@ struct pt_regs;
 #ifndef __OPTIMIZE__
 #define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
 #else
-#define BUILD_BUG_ON(condition)                                                \
-       do {                                                            \
-               bool __cond = !!(condition);                            \
-               extern void __build_bug_on_failed(void)                 \
-                       __compiletime_error("BUILD_BUG_ON failed");     \
-               if (__cond)                                             \
-                       __build_bug_on_failed();                        \
-               __compiletime_error_fallback(__cond);                   \
-       } while (0)
+#define BUILD_BUG_ON(condition) \
+       BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
 #endif
 
 /**
@@ -78,12 +81,7 @@ struct pt_regs;
  * build time, you should use BUILD_BUG to detect if it is
  * unexpectedly used.
  */
-#define BUILD_BUG()                                            \
-       do {                                                    \
-               extern void __build_bug_failed(void)            \
-                       __compiletime_error("BUILD_BUG failed");\
-               __build_bug_failed();                           \
-       } while (0)
+#define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed")
 
 #endif /* __CHECKER__ */
 

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 423bb6bd660ff543fe38f7b3763406327909cfe5..10b8f23fab0f0ad0dfdfcc72ab79b44129772e3d 100644 (file)
--- 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(),