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cf66bb93e0
Since GCC 4.4, there have been __builtin_bswap32() and __builtin_bswap16() intrinsics. A __builtin_bswap16() came a little later (4.6 for PowerPC, 48 for other platforms). By using these instead of the inline assembler that most architectures have in their __arch_swabXX() macros, we let the compiler see what's actually happening. The resulting code should be at least as good, and much *better* in the cases where it can be combined with a nearby load or store, using a load-and-byteswap or store-and-byteswap instruction (e.g. lwbrx/stwbrx on PowerPC, movbe on Atom). When GCC is sufficiently recent *and* the architecture opts in to using the intrinsics by setting CONFIG_ARCH_USE_BUILTIN_BSWAP, they will be used in preference to the __arch_swabXX() macros. An architecture which does not set ARCH_USE_BUILTIN_BSWAP will continue to use its own hand-crafted macros. Signed-off-by: David Woodhouse <David.Woodhouse@intel.com> Acked-by: H. Peter Anvin <hpa@linux.intel.com>
76 lines
2.5 KiB
C
76 lines
2.5 KiB
C
#ifndef __LINUX_COMPILER_H
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#error "Please don't include <linux/compiler-gcc4.h> directly, include <linux/compiler.h> instead."
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#endif
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/* GCC 4.1.[01] miscompiles __weak */
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#ifdef __KERNEL__
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# if __GNUC_MINOR__ == 1 && __GNUC_PATCHLEVEL__ <= 1
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# error Your version of gcc miscompiles the __weak directive
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# endif
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#endif
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#define __used __attribute__((__used__))
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#define __must_check __attribute__((warn_unused_result))
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#define __compiler_offsetof(a,b) __builtin_offsetof(a,b)
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#if __GNUC_MINOR__ >= 3
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/* Mark functions as cold. gcc will assume any path leading to a call
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to them will be unlikely. This means a lot of manual unlikely()s
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are unnecessary now for any paths leading to the usual suspects
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like BUG(), printk(), panic() etc. [but let's keep them for now for
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older compilers]
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Early snapshots of gcc 4.3 don't support this and we can't detect this
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in the preprocessor, but we can live with this because they're unreleased.
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Maketime probing would be overkill here.
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gcc also has a __attribute__((__hot__)) to move hot functions into
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a special section, but I don't see any sense in this right now in
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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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* Mark a position in code as unreachable. This can be used to
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* suppress control flow warnings after asm blocks that transfer
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* control elsewhere.
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*
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* Early snapshots of gcc 4.5 don't support this and we can't detect
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* this in the preprocessor, but we can live with this because they're
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* unreleased. Really, we need to have autoconf for the kernel.
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*/
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#define unreachable() __builtin_unreachable()
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/* Mark a function definition as prohibited from being cloned. */
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#define __noclone __attribute__((__noclone__))
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#endif
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#endif
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#if __GNUC_MINOR__ >= 6
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/*
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* Tell the optimizer that something else uses this function or variable.
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*/
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#define __visible __attribute__((externally_visible))
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#endif
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#if __GNUC_MINOR__ > 0
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#define __compiletime_object_size(obj) __builtin_object_size(obj, 0)
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#endif
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#if __GNUC_MINOR__ >= 3 && !defined(__CHECKER__)
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#define __compiletime_warning(message) __attribute__((warning(message)))
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#define __compiletime_error(message) __attribute__((error(message)))
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#endif
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#ifdef CONFIG_ARCH_USE_BUILTIN_BSWAP
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#if __GNUC_MINOR__ >= 4
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#define __HAVE_BUILTIN_BSWAP32__
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#define __HAVE_BUILTIN_BSWAP64__
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#endif
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#if __GNUC_MINOR__ >= 8 || (defined(__powerpc__) && __GNUC_MINOR__ >= 6)
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#define __HAVE_BUILTIN_BSWAP16__
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#endif
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#endif
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