cregit-Linux how code gets into the kernel

Release 4.7 include/linux/compiler-gcc.h

Directory: include/linux
#ifndef __LINUX_COMPILER_H
#error "Please don't include <linux/compiler-gcc.h> directly, include <linux/compiler.h> instead."
#endif

/*
 * Common definitions for all gcc versions go here.
 */

#define GCC_VERSION (__GNUC__ * 10000               \
                     + __GNUC_MINOR__ * 100     \
                     + __GNUC_PATCHLEVEL__)

/* Optimization barrier */

/* The "volatile" is due to gcc bugs */

#define barrier() __asm__ __volatile__("": : :"memory")
/*
 * This version is i.e. to prevent dead stores elimination on @ptr
 * where gcc and llvm may behave differently when otherwise using
 * normal barrier(): while gcc behavior gets along with a normal
 * barrier(), llvm needs an explicit input variable to be assumed
 * clobbered. The issue is as follows: while the inline asm might
 * access any memory it wants, the compiler could have fit all of
 * @ptr into memory registers instead, and since @ptr never escaped
 * from that, it proofed that the inline asm wasn't touching any of
 * it. This version works well with both compilers, i.e. we're telling
 * the compiler that the inline asm absolutely may see the contents
 * of @ptr. See also: https://llvm.org/bugs/show_bug.cgi?id=15495
 */

#define barrier_data(ptr) __asm__ __volatile__("": :"r"(ptr) :"memory")

/*
 * This macro obfuscates arithmetic on a variable address so that gcc
 * shouldn't recognize the original var, and make assumptions about it.
 *
 * This is needed because the C standard makes it undefined to do
 * pointer arithmetic on "objects" outside their boundaries and the
 * gcc optimizers assume this is the case. In particular they
 * assume such arithmetic does not wrap.
 *
 * A miscompilation has been observed because of this on PPC.
 * To work around it we hide the relationship of the pointer and the object
 * using this macro.
 *
 * Versions of the ppc64 compiler before 4.1 had a bug where use of
 * RELOC_HIDE could trash r30. The bug can be worked around by changing
 * the inline assembly constraint from =g to =r, in this particular
 * case either is valid.
 */

#define RELOC_HIDE(ptr, off)						\
({                                                                      \
        unsigned long __ptr;                                            \
        __asm__ ("" : "=r"(__ptr) : "0"(ptr));                          \
        (typeof(ptr)) (__ptr + (off));                                  \
})

/* Make the optimizer believe the variable can be manipulated arbitrarily. */

#define OPTIMIZER_HIDE_VAR(var)						\
	__asm__ ("" : "=r" (var) : "0" (var))

#ifdef __CHECKER__

#define __must_be_array(a)	0
#else
/* &a[0] degrades to a pointer: a different type from an array */

#define __must_be_array(a)	BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
#endif

/*
 * Force always-inline if the user requests it so via the .config,
 * or if gcc is too old:
 */
#if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) ||		\
    !defined(CONFIG_OPTIMIZE_INLINING) || (__GNUC__ < 4)

#define inline		inline          __attribute__((always_inline)) notrace

#define __inline__	__inline__      __attribute__((always_inline)) notrace

#define __inline	__inline        __attribute__((always_inline)) notrace
#else
/* A lot of inline functions can cause havoc with function tracing */

#define inline		inline          notrace

#define __inline__	__inline__      notrace

#define __inline	__inline        notrace
#endif


#define __always_inline	inline __attribute__((always_inline))

#define  noinline	__attribute__((noinline))


#define __deprecated	__attribute__((deprecated))

#define __packed	__attribute__((packed))

#define __weak		__attribute__((weak))

#define __alias(symbol)	__attribute__((alias(#symbol)))

/*
 * it doesn't make sense on ARM (currently the only user of __naked)
 * to trace naked functions because then mcount is called without
 * stack and frame pointer being set up and there is no chance to
 * restore the lr register to the value before mcount was called.
 *
 * The asm() bodies of naked functions often depend on standard calling
 * conventions, therefore they must be noinline and noclone.
 *
 * GCC 4.[56] currently fail to enforce this, so we must do so ourselves.
 * See GCC PR44290.
 */

#define __naked		__attribute__((naked)) noinline __noclone notrace


#define __noreturn	__attribute__((noreturn))

/*
 * From the GCC manual:
 *
 * Many functions have no effects except the return value and their
 * return value depends only on the parameters and/or global
 * variables.  Such a function can be subject to common subexpression
 * elimination and loop optimization just as an arithmetic operator
 * would be.
 * [...]
 */

#define __pure			__attribute__((pure))

#define __aligned(x)		__attribute__((aligned(x)))

#define __printf(a, b)		__attribute__((format(printf, a, b)))

#define __scanf(a, b)		__attribute__((format(scanf, a, b)))

#define __attribute_const__	__attribute__((__const__))

#define __maybe_unused		__attribute__((unused))

#define __always_unused		__attribute__((unused))

/* gcc version specific checks */

#if GCC_VERSION < 30200
# error Sorry, your compiler is too old - please upgrade it.
#endif

#if GCC_VERSION < 30300

# define __used			__attribute__((__unused__))
#else

# define __used			__attribute__((__used__))
#endif

#ifdef CONFIG_GCOV_KERNEL
# if GCC_VERSION < 30400
#   error "GCOV profiling support for gcc versions below 3.4 not included"
# endif /* __GNUC_MINOR__ */
#endif /* CONFIG_GCOV_KERNEL */

#if GCC_VERSION >= 30400

#define __must_check		__attribute__((warn_unused_result))

#define __malloc		__attribute__((__malloc__))
#endif

#if GCC_VERSION >= 40000

/* GCC 4.1.[01] miscompiles __weak */
#ifdef __KERNEL__
# if GCC_VERSION >= 40100 &&  GCC_VERSION <= 40101
#  error Your version of gcc miscompiles the __weak directive
# endif
#endif


#define __used			__attribute__((__used__))

#define __compiler_offsetof(a, b)					\
	__builtin_offsetof(a, b)

#if GCC_VERSION >= 40100 && GCC_VERSION < 40600

# define __compiletime_object_size(obj) __builtin_object_size(obj, 0)
#endif

#if GCC_VERSION >= 40300
/* Mark functions as cold. gcc will assume any path leading to a call
 * to them will be unlikely.  This means a lot of manual unlikely()s
 * are unnecessary now for any paths leading to the usual suspects
 * like BUG(), printk(), panic() etc. [but let's keep them for now for
 * older compilers]
 *
 * Early snapshots of gcc 4.3 don't support this and we can't detect this
 * in the preprocessor, but we can live with this because they're unreleased.
 * Maketime probing would be overkill here.
 *
 * gcc also has a __attribute__((__hot__)) to move hot functions into
 * a special section, but I don't see any sense in this right now in
 * the kernel context
 */

#define __cold			__attribute__((__cold__))


#define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)

#ifndef __CHECKER__

# define __compiletime_warning(message) __attribute__((warning(message)))

# define __compiletime_error(message) __attribute__((error(message)))
#endif /* __CHECKER__ */
#endif /* GCC_VERSION >= 40300 */

#if GCC_VERSION >= 40500
/*
 * Mark a position in code as unreachable.  This can be used to
 * suppress control flow warnings after asm blocks that transfer
 * control elsewhere.
 *
 * Early snapshots of gcc 4.5 don't support this and we can't detect
 * this in the preprocessor, but we can live with this because they're
 * unreleased.  Really, we need to have autoconf for the kernel.
 */

#define unreachable() __builtin_unreachable()

/* Mark a function definition as prohibited from being cloned. */

#define __noclone	__attribute__((__noclone__, __optimize__("no-tracer")))

#endif /* GCC_VERSION >= 40500 */

#if GCC_VERSION >= 40600
/*
 * When used with Link Time Optimization, gcc can optimize away C functions or
 * variables which are referenced only from assembly code.  __visible tells the
 * optimizer that something else uses this function or variable, thus preventing
 * this.
 */

#define __visible	__attribute__((externally_visible))
#endif


#if GCC_VERSION >= 40900 && !defined(__CHECKER__)
/*
 * __assume_aligned(n, k): Tell the optimizer that the returned
 * pointer can be assumed to be k modulo n. The second argument is
 * optional (default 0), so we use a variadic macro to make the
 * shorthand.
 *
 * Beware: Do not apply this to functions which may return
 * ERR_PTRs. Also, it is probably unwise to apply it to functions
 * returning extra information in the low bits (but in that case the
 * compiler should see some alignment anyway, when the return value is
 * massaged by 'flags = ptr & 3; ptr &= ~3;').
 */

#define __assume_aligned(a, ...) __attribute__((__assume_aligned__(a, ## __VA_ARGS__)))
#endif

/*
 * GCC 'asm goto' miscompiles certain code sequences:
 *
 *   http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670
 *
 * Work it around via a compiler barrier quirk suggested by Jakub Jelinek.
 *
 * (asm goto is automatically volatile - the naming reflects this.)
 */

#define asm_volatile_goto(x...)	do { asm goto(x); asm (""); } while (0)

#ifdef CONFIG_ARCH_USE_BUILTIN_BSWAP
#if GCC_VERSION >= 40400

#define __HAVE_BUILTIN_BSWAP32__

#define __HAVE_BUILTIN_BSWAP64__
#endif
#if GCC_VERSION >= 40800

#define __HAVE_BUILTIN_BSWAP16__
#endif
#endif /* CONFIG_ARCH_USE_BUILTIN_BSWAP */

#if GCC_VERSION >= 50000

#define KASAN_ABI_VERSION 4
#elif GCC_VERSION >= 40902

#define KASAN_ABI_VERSION 3
#endif

#if GCC_VERSION >= 40902
/*
 * Tell the compiler that address safety instrumentation (KASAN)
 * should not be applied to that function.
 * Conflicts with inlining: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
 */

#define __no_sanitize_address __attribute__((no_sanitize_address))
#endif

#endif	/* gcc version >= 40000 specific checks */

#if !defined(__noclone)

#define __noclone	
/* not needed */
#endif

#if !defined(__no_sanitize_address)

#define __no_sanitize_address
#endif

/*
 * A trick to suppress uninitialized variable warning without generating any
 * code
 */

#define uninitialized_var(x) x = x

Overall Contributors
PersonTokensPropCommitsCommitProp
joe perchesjoe perches25349.13%39.38%


robert p. j. dayrobert p. j. day428.16%26.25%


andrew mortonandrew morton356.80%39.38%


andrey ryabininandrey ryabinin316.02%26.25%


rasmus villemoesrasmus villemoes275.24%39.38%


ingo molnaringo molnar234.47%39.38%


steven rostedtsteven rostedt183.50%26.25%


mikael petterssonmikael pettersson142.72%13.12%


linus torvaldslinus torvalds132.52%13.12%


kosaki motohirokosaki motohiro132.52%13.12%


rusty russellrusty russell81.55%26.25%


daniel borkmanndaniel borkmann81.55%13.12%


borislav petkovborislav petkov81.55%13.12%


cesar eduardo barroscesar eduardo barros81.55%13.12%


david rientjesdavid rientjes40.78%13.12%


li zefanli zefan40.78%13.12%


daniel santosdaniel santos30.58%13.12%


andi kleenandi kleen10.19%13.12%


ralf baechleralf baechle10.19%13.12%


paolo bonzinipaolo bonzini10.19%13.12%


Total515100.00%32100.00%

  
Directory: include/linux



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