c361d3e543
Prior to the introduction of __attribute__((error("msg"))) in gcc 4.3,
creating compile-time errors required a little trickery.
BUILD_BUG{,_ON} uses this attribute when available to generate
compile-time errors, but also uses the negative-sized array trick for
older compilers, resulting in two error messages in some cases. The
reason it's "some" cases is that as of gcc 4.4, the negative-sized array
will not create an error in some situations, like inline functions.
This patch replaces the negative-sized array code with the new
__compiletime_error_fallback() macro which expands to the same thing
unless the the error attribute is available, in which case it expands to
do{}while(0), resulting in exactly one compile-time error on all
versions of gcc.
Note that we are not changing the negative-sized array code for the
unoptimized version of BUILD_BUG_ON, since it has the potential to catch
problems that would be disabled in later versions of gcc were
__compiletime_error_fallback used. The reason is that that an
unoptimized build can't always remove calls to an error-attributed
function call (like we are using) that should effectively become dead
code if it were optimized. However, using a negative-sized array with a
similar value will not result in an false-positive (error). The only
caveat being that it will also fail to catch valid conditions, which we
should be expecting in an unoptimized build anyway.
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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
115 lines
3.5 KiB
C
115 lines
3.5 KiB
C
#ifndef _LINUX_BUG_H
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#define _LINUX_BUG_H
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#include <asm/bug.h>
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#include <linux/compiler.h>
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enum bug_trap_type {
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BUG_TRAP_TYPE_NONE = 0,
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BUG_TRAP_TYPE_WARN = 1,
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BUG_TRAP_TYPE_BUG = 2,
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};
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struct pt_regs;
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#ifdef __CHECKER__
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#define BUILD_BUG_ON_NOT_POWER_OF_2(n) (0)
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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_INVALID(e) (0)
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#define BUILD_BUG_ON(condition) (0)
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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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#define BUILD_BUG_ON_NOT_POWER_OF_2(n) \
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BUILD_BUG_ON((n) == 0 || (((n) & ((n) - 1)) != 0))
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/* Force a compilation error if condition is true, but also produce a
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result (of value 0 and type size_t), so the expression can be used
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e.g. in a structure initializer (or where-ever else comma expressions
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aren't permitted). */
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#define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:-!!(e); }))
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#define BUILD_BUG_ON_NULL(e) ((void *)sizeof(struct { int:-!!(e); }))
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/*
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* BUILD_BUG_ON_INVALID() permits the compiler to check the validity of the
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* expression but avoids the generation of any code, even if that expression
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* has side-effects.
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*/
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#define BUILD_BUG_ON_INVALID(e) ((void)(sizeof((__force long)(e))))
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/**
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* BUILD_BUG_ON - break compile if a condition is true.
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* @condition: the condition which the compiler should know is false.
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*
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* If you have some code which relies on certain constants being equal, or
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* some other compile-time-evaluated condition, you should use BUILD_BUG_ON to
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* detect if someone changes it.
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*
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* The implementation uses gcc's reluctance to create a negative array, but gcc
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* (as of 4.4) only emits that error for obvious cases (e.g. not arguments to
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* inline functions). Luckily, in 4.3 they added the "error" function
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* attribute just for this type of case. Thus, we use a negative sized array
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* (should always create an error on gcc versions older than 4.4) and then call
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* an undefined function with the error attribute (should always create an
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* error on gcc 4.3 and later). If for some reason, neither creates a
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* compile-time error, we'll still have a link-time error, which is harder to
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* track down.
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*/
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#ifndef __OPTIMIZE__
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#define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
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#else
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#define BUILD_BUG_ON(condition) \
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do { \
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bool __cond = !!(condition); \
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extern void __build_bug_on_failed(void) \
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__compiletime_error("BUILD_BUG_ON failed"); \
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if (__cond) \
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__build_bug_on_failed(); \
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__compiletime_error_fallback(__cond); \
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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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__compiletime_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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#ifdef CONFIG_GENERIC_BUG
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#include <asm-generic/bug.h>
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static inline int is_warning_bug(const struct bug_entry *bug)
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{
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return bug->flags & BUGFLAG_WARNING;
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}
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const struct bug_entry *find_bug(unsigned long bugaddr);
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enum bug_trap_type report_bug(unsigned long bug_addr, struct pt_regs *regs);
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/* These are defined by the architecture */
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int is_valid_bugaddr(unsigned long addr);
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#else /* !CONFIG_GENERIC_BUG */
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static inline enum bug_trap_type report_bug(unsigned long bug_addr,
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struct pt_regs *regs)
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{
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return BUG_TRAP_TYPE_BUG;
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}
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#endif /* CONFIG_GENERIC_BUG */
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#endif /* _LINUX_BUG_H */
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