a586df067a
gcc 4.3 supports a new __attribute__((__cold__)) to mark functions cold. Any path directly leading to a call of this function will be unlikely. And gcc will try to generate smaller code for the function itself. Please use with care. The code generation advantage isn't large and in most cases it is not worth uglifying code with this. This patch marks some common error functions like panic(), printk() as cold. This will longer term make many unlikely()s unnecessary, although we can keep them for now for older compilers. BUG is not marked cold because there is currently no way to tell gcc to mark a inline function told. Also all __init and __exit functions are marked cold. With a non -Os build this will tell the compiler to generate slightly smaller code for them. I think it currently only uses less alignments for labels, but that might change in the future. One disadvantage over *likely() is that they cannot be easily instrumented to verify them. Another drawback is that only the latest gcc 4.3 snapshots support this. Unfortunately we cannot detect this using the preprocessor. This means older snapshots will fail now. I don't think that's a problem because they are unreleased compilers that nobody should be using. gcc also has a __hot__ attribute, but I don't see any sense in using this in the kernel right now. But someday I hope gcc will be able to use more aggressive optimizing for hot functions even in -Os, if that happens it should be added. Includes compile fix from Thomas Gleixner. Cc: Jan Hubicka <jh@suse.cz> Signed-off-by: Andi Kleen <ak@suse.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
186 lines
4.9 KiB
C
186 lines
4.9 KiB
C
#ifndef __LINUX_COMPILER_H
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#define __LINUX_COMPILER_H
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#ifndef __ASSEMBLY__
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#ifdef __CHECKER__
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# define __user __attribute__((noderef, address_space(1)))
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# define __kernel /* default address space */
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# define __safe __attribute__((safe))
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# define __force __attribute__((force))
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# define __nocast __attribute__((nocast))
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# define __iomem __attribute__((noderef, address_space(2)))
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# define __acquires(x) __attribute__((context(x,0,1)))
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# define __releases(x) __attribute__((context(x,1,0)))
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# define __acquire(x) __context__(x,1)
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# define __release(x) __context__(x,-1)
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# define __cond_lock(x,c) ((c) ? ({ __acquire(x); 1; }) : 0)
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extern void __chk_user_ptr(const void __user *);
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extern void __chk_io_ptr(const void __iomem *);
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#else
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# define __user
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# define __kernel
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# define __safe
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# define __force
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# define __nocast
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# define __iomem
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# define __chk_user_ptr(x) (void)0
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# define __chk_io_ptr(x) (void)0
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# define __builtin_warning(x, y...) (1)
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# define __acquires(x)
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# define __releases(x)
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# define __acquire(x) (void)0
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# define __release(x) (void)0
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# define __cond_lock(x,c) (c)
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#endif
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#ifdef __KERNEL__
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#if __GNUC__ >= 4
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# include <linux/compiler-gcc4.h>
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#elif __GNUC__ == 3 && __GNUC_MINOR__ >= 2
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# include <linux/compiler-gcc3.h>
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#else
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# error Sorry, your compiler is too old/not recognized.
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#endif
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/* Intel compiler defines __GNUC__. So we will overwrite implementations
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* coming from above header files here
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*/
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#ifdef __INTEL_COMPILER
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# include <linux/compiler-intel.h>
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#endif
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/*
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* Generic compiler-dependent macros required for kernel
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* build go below this comment. Actual compiler/compiler version
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* specific implementations come from the above header files
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*/
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#define likely(x) __builtin_expect(!!(x), 1)
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#define unlikely(x) __builtin_expect(!!(x), 0)
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/* Optimization barrier */
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#ifndef barrier
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# define barrier() __memory_barrier()
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#endif
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#ifndef RELOC_HIDE
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# define RELOC_HIDE(ptr, off) \
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({ unsigned long __ptr; \
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__ptr = (unsigned long) (ptr); \
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(typeof(ptr)) (__ptr + (off)); })
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#endif
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#endif /* __KERNEL__ */
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#endif /* __ASSEMBLY__ */
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#ifdef __KERNEL__
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/*
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* Allow us to mark functions as 'deprecated' and have gcc emit a nice
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* warning for each use, in hopes of speeding the functions removal.
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* Usage is:
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* int __deprecated foo(void)
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*/
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#ifndef __deprecated
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# define __deprecated /* unimplemented */
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#endif
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#ifdef MODULE
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#define __deprecated_for_modules __deprecated
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#else
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#define __deprecated_for_modules
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#endif
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#ifndef __must_check
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#define __must_check
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#endif
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#ifndef CONFIG_ENABLE_MUST_CHECK
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#undef __must_check
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#define __must_check
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#endif
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/*
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* Allow us to avoid 'defined but not used' warnings on functions and data,
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* as well as force them to be emitted to the assembly file.
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*
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* As of gcc 3.4, static functions that are not marked with attribute((used))
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* may be elided from the assembly file. As of gcc 3.4, static data not so
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* marked will not be elided, but this may change in a future gcc version.
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*
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* NOTE: Because distributions shipped with a backported unit-at-a-time
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* compiler in gcc 3.3, we must define __used to be __attribute__((used))
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* for gcc >=3.3 instead of 3.4.
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*
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* In prior versions of gcc, such functions and data would be emitted, but
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* would be warned about except with attribute((unused)).
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*
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* Mark functions that are referenced only in inline assembly as __used so
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* the code is emitted even though it appears to be unreferenced.
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*/
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#ifndef __attribute_used__
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# define __attribute_used__ /* deprecated */
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#endif
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#ifndef __used
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# define __used /* unimplemented */
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#endif
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#ifndef __maybe_unused
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# define __maybe_unused /* unimplemented */
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#endif
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/*
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* From the GCC manual:
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*
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* Many functions have no effects except the return value and their
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* return value depends only on the parameters and/or global
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* variables. Such a function can be subject to common subexpression
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* elimination and loop optimization just as an arithmetic operator
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* would be.
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* [...]
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*/
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#ifndef __attribute_pure__
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# define __attribute_pure__ /* unimplemented */
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#endif
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#ifndef noinline
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#define noinline
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#endif
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#ifndef __always_inline
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#define __always_inline inline
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#endif
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#endif /* __KERNEL__ */
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/*
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* From the GCC manual:
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*
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* Many functions do not examine any values except their arguments,
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* and have no effects except the return value. Basically this is
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* just slightly more strict class than the `pure' attribute above,
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* since function is not allowed to read global memory.
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*
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* Note that a function that has pointer arguments and examines the
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* data pointed to must _not_ be declared `const'. Likewise, a
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* function that calls a non-`const' function usually must not be
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* `const'. It does not make sense for a `const' function to return
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* `void'.
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*/
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#ifndef __attribute_const__
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# define __attribute_const__ /* unimplemented */
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#endif
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/*
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* Tell gcc if a function is cold. The compiler will assume any path
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* directly leading to the call is unlikely.
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*/
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#ifndef __cold
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#define __cold
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#endif
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#endif /* __LINUX_COMPILER_H */
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