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>
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@ -29,6 +29,7 @@
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the kernel context */
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#define __cold __attribute__((__cold__))
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#define __linktime_error(message) __attribute__((__error__(message)))
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#if __GNUC_MINOR__ >= 5
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/*
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@ -293,7 +293,9 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
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#ifndef __compiletime_error
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# define __compiletime_error(message)
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#endif
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#ifndef __linktime_error
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# define __linktime_error(message)
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#endif
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/*
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* Prevent the compiler from merging or refetching accesses. The compiler
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* is also forbidden from reordering successive instances of ACCESS_ONCE(),
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@ -665,6 +665,7 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { }
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#define BUILD_BUG_ON_ZERO(e) (0)
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#define BUILD_BUG_ON_NULL(e) ((void*)0)
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#define BUILD_BUG_ON(condition)
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#define BUILD_BUG() (0)
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#else /* __CHECKER__ */
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/* Force a compilation error if a constant expression is not a power of 2 */
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@ -703,6 +704,21 @@ extern int __build_bug_on_failed;
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if (condition) __build_bug_on_failed = 1; \
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} while(0)
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#endif
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/**
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* BUILD_BUG - break compile if used.
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*
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* If you have some code that you expect the compiler to eliminate at
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* build time, you should use BUILD_BUG to detect if it is
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* unexpectedly used.
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*/
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#define BUILD_BUG() \
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do { \
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extern void __build_bug_failed(void) \
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__linktime_error("BUILD_BUG failed"); \
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__build_bug_failed(); \
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} while (0)
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#endif /* __CHECKER__ */
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/* Trap pasters of __FUNCTION__ at compile-time */
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