From: David Daney <david.daney@xxxxxxxxxx>
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@xxxxxxxxxx>
---
include/linux/compiler-gcc4.h | 1 +
include/linux/compiler.h | 4 +++-
include/linux/kernel.h | 16 ++++++++++++++++
3 files changed, 20 insertions(+), 1 deletions(-)
diff --git a/include/linux/compiler-gcc4.h b/include/linux/compiler-gcc4.h
index dfadc96..2f40791 100644
--- a/include/linux/compiler-gcc4.h
+++ b/include/linux/compiler-gcc4.h
@@ -29,6 +29,7 @@
the kernel context */
#define __cold __attribute__((__cold__))
+#define __linktime_error(message) __attribute__((__error__(message)))
#if __GNUC_MINOR__ >= 5
/*
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 320d6c9..4a24354 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -293,7 +293,9 @@ 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 b93c66e..e30002f 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -666,6 +666,7 @@ 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 */
@@ -704,6 +705,21 @@ 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_ON_USED 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 */
--
1.7.2.3
--
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