include/linux/compiler-gcc.h - kernel/bruno - Git at Google

 #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))
 #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 || (defined(__powerpc__) && GCC_VERSION >= 40600)
 #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
	#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))
	#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 \|\| (defined(__powerpc__) && GCC_VERSION >= 40600)
	#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