From 29efbc6aea9d9bd9aa9870a9afc1882046303cf9 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Thu, 30 Aug 2018 19:07:27 +0200 Subject: [PATCH 01/17] Compiler Attributes: remove unused attributes __optimize and __deprecate_for_modules are unused in the whole kernel tree. Simply drop them. Tested-by: Sedat Dilek # on top of v4.19-rc5, clang 7 Reviewed-by: Nick Desaulniers Reviewed-by: Luc Van Oostenryck Signed-off-by: Miguel Ojeda --- include/linux/compiler-gcc.h | 2 -- include/linux/compiler.h | 4 ---- include/linux/compiler_types.h | 1 - 3 files changed, 7 deletions(-) diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h index 4d36b27214fd..1302b425e625 100644 --- a/include/linux/compiler-gcc.h +++ b/include/linux/compiler-gcc.h @@ -81,8 +81,6 @@ #define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__) -#define __optimize(level) __attribute__((__optimize__(level))) - #define __compiletime_object_size(obj) __builtin_object_size(obj, 0) #ifndef __CHECKER__ diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 681d866efb1e..7c0157d50964 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -301,10 +301,6 @@ static inline void *offset_to_ptr(const int *off) #endif /* __ASSEMBLY__ */ -#ifndef __optimize -# define __optimize(level) -#endif - /* Compile time object size, -1 for unknown */ #ifndef __compiletime_object_size # define __compiletime_object_size(obj) -1 diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index db192becfec4..a19562cb047c 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -108,7 +108,6 @@ struct ftrace_likely_data { /* Don't. Just don't. */ #define __deprecated -#define __deprecated_for_modules #endif /* __KERNEL__ */ From 5c67a52f3da0f0d22764f2daec417702695a8112 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Thu, 30 Aug 2018 19:13:37 +0200 Subject: [PATCH 02/17] Compiler Attributes: always use the extra-underscores syntax The attribute syntax optionally allows to surround attribute names with "__" in order to avoid collisions with macros of the same name (see https://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html). This homogenizes all attributes to use the syntax with underscores. While there are currently only a handful of cases of some TUs defining macros like "error" which may collide with the attributes, this should prevent futures surprises. This has been done only for "standard" attributes supported by the major compilers. In other words, those of third-party tools (e.g. sparse, plugins...) have not been changed for the moment. Tested-by: Sedat Dilek # on top of v4.19-rc5, clang 7 Reviewed-by: Nick Desaulniers Reviewed-by: Luc Van Oostenryck Signed-off-by: Miguel Ojeda --- include/linux/compiler-clang.h | 2 +- include/linux/compiler-gcc.h | 12 +++++----- include/linux/compiler-intel.h | 2 +- include/linux/compiler.h | 8 +++---- include/linux/compiler_types.h | 42 +++++++++++++++++----------------- 5 files changed, 33 insertions(+), 33 deletions(-) diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h index b1ce500fe8b3..d11cad61ba5c 100644 --- a/include/linux/compiler-clang.h +++ b/include/linux/compiler-clang.h @@ -21,7 +21,7 @@ #define __SANITIZE_ADDRESS__ #endif -#define __no_sanitize_address __attribute__((no_sanitize("address"))) +#define __no_sanitize_address __attribute__((__no_sanitize__("address"))) /* * Not all versions of clang implement the the type-generic versions diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h index 1302b425e625..7a1de7683df5 100644 --- a/include/linux/compiler-gcc.h +++ b/include/linux/compiler-gcc.h @@ -76,7 +76,7 @@ #endif #ifdef RETPOLINE -#define __noretpoline __attribute__((indirect_branch("keep"))) +#define __noretpoline __attribute__((__indirect_branch__("keep"))) #endif #define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__) @@ -84,8 +84,8 @@ #define __compiletime_object_size(obj) __builtin_object_size(obj, 0) #ifndef __CHECKER__ -#define __compiletime_warning(message) __attribute__((warning(message))) -#define __compiletime_error(message) __attribute__((error(message))) +#define __compiletime_warning(message) __attribute__((__warning__(message))) +#define __compiletime_error(message) __attribute__((__error__(message))) #ifdef LATENT_ENTROPY_PLUGIN #define __latent_entropy __attribute__((latent_entropy)) @@ -134,7 +134,7 @@ * optimizer that something else uses this function or variable, thus preventing * this. */ -#define __visible __attribute__((externally_visible)) +#define __visible __attribute__((__externally_visible__)) /* gcc version specific checks */ @@ -191,7 +191,7 @@ * 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)) +#define __no_sanitize_address __attribute__((__no_sanitize_address__)) #endif #if GCC_VERSION >= 50100 @@ -199,7 +199,7 @@ * Mark structures as requiring designated initializers. * https://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html */ -#define __designated_init __attribute__((designated_init)) +#define __designated_init __attribute__((__designated_init__)) #define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1 #endif diff --git a/include/linux/compiler-intel.h b/include/linux/compiler-intel.h index 4c7f9befa9f6..fef8bb3e53ef 100644 --- a/include/linux/compiler-intel.h +++ b/include/linux/compiler-intel.h @@ -42,4 +42,4 @@ * and may be redefined here because they should not be shared with other * compilers, like clang. */ -#define __visible __attribute__((externally_visible)) +#define __visible __attribute__((__externally_visible__)) diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 7c0157d50964..ec4a28bad2c6 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -24,7 +24,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, long ______r; \ static struct ftrace_likely_data \ __attribute__((__aligned__(4))) \ - __attribute__((section("_ftrace_annotated_branch"))) \ + __attribute__((__section__("_ftrace_annotated_branch"))) \ ______f = { \ .data.func = __func__, \ .data.file = __FILE__, \ @@ -60,7 +60,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, int ______r; \ static struct ftrace_branch_data \ __attribute__((__aligned__(4))) \ - __attribute__((section("_ftrace_branch"))) \ + __attribute__((__section__("_ftrace_branch"))) \ ______f = { \ .func = __func__, \ .file = __FILE__, \ @@ -146,7 +146,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, extern typeof(sym) sym; \ static const unsigned long __kentry_##sym \ __used \ - __attribute__((section("___kentry" "+" #sym ), used)) \ + __attribute__((__section__("___kentry" "+" #sym ), used)) \ = (unsigned long)&sym; #endif @@ -287,7 +287,7 @@ unsigned long read_word_at_a_time(const void *addr) * visible to the compiler. */ #define __ADDRESSABLE(sym) \ - static void * __attribute__((section(".discard.addressable"), used)) \ + static void * __attribute__((__section__(".discard.addressable"), used)) \ __PASTE(__addressable_##sym, __LINE__) = (void *)&sym; /** diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index a19562cb047c..8fbdd47dd3d0 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -195,26 +195,26 @@ struct ftrace_likely_data { * would be. * [...] */ -#define __pure __attribute__((pure)) -#define __aligned(x) __attribute__((aligned(x))) -#define __aligned_largest __attribute__((aligned)) -#define __printf(a, b) __attribute__((format(printf, a, b))) -#define __scanf(a, b) __attribute__((format(scanf, a, b))) -#define __maybe_unused __attribute__((unused)) -#define __always_unused __attribute__((unused)) -#define __mode(x) __attribute__((mode(x))) +#define __pure __attribute__((__pure__)) +#define __aligned(x) __attribute__((__aligned__(x))) +#define __aligned_largest __attribute__((__aligned__)) +#define __printf(a, b) __attribute__((__format__(printf, a, b))) +#define __scanf(a, b) __attribute__((__format__(scanf, a, b))) +#define __maybe_unused __attribute__((__unused__)) +#define __always_unused __attribute__((__unused__)) +#define __mode(x) __attribute__((__mode__(x))) #define __malloc __attribute__((__malloc__)) #define __used __attribute__((__used__)) -#define __noreturn __attribute__((noreturn)) -#define __packed __attribute__((packed)) -#define __weak __attribute__((weak)) -#define __alias(symbol) __attribute__((alias(#symbol))) -#define __cold __attribute__((cold)) +#define __noreturn __attribute__((__noreturn__)) +#define __packed __attribute__((__packed__)) +#define __weak __attribute__((__weak__)) +#define __alias(symbol) __attribute__((__alias__(#symbol))) +#define __cold __attribute__((__cold__)) #define __section(S) __attribute__((__section__(#S))) #ifdef CONFIG_ENABLE_MUST_CHECK -#define __must_check __attribute__((warn_unused_result)) +#define __must_check __attribute__((__warn_unused_result__)) #else #define __must_check #endif @@ -222,7 +222,7 @@ struct ftrace_likely_data { #if defined(CC_USING_HOTPATCH) && !defined(__CHECKER__) #define notrace __attribute__((hotpatch(0, 0))) #else -#define notrace __attribute__((no_instrument_function)) +#define notrace __attribute__((__no_instrument_function__)) #endif /* @@ -231,7 +231,7 @@ struct ftrace_likely_data { * stack and frame pointer being set up and there is no chance to * restore the lr register to the value before mcount was called. */ -#define __naked __attribute__((naked)) notrace +#define __naked __attribute__((__naked__)) notrace #define __compiler_offsetof(a, b) __builtin_offsetof(a, b) @@ -242,7 +242,7 @@ struct ftrace_likely_data { * defined so the gnu89 semantics are the default. */ #ifdef __GNUC_STDC_INLINE__ -# define __gnu_inline __attribute__((gnu_inline)) +# define __gnu_inline __attribute__((__gnu_inline__)) #else # define __gnu_inline #endif @@ -262,17 +262,17 @@ struct ftrace_likely_data { #if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) || \ !defined(CONFIG_OPTIMIZE_INLINING) #define inline \ - inline __attribute__((always_inline, unused)) notrace __gnu_inline + inline __attribute__((__always_inline__, __unused__)) notrace __gnu_inline #else -#define inline inline __attribute__((unused)) notrace __gnu_inline +#define inline inline __attribute__((__unused__)) notrace __gnu_inline #endif #define __inline__ inline #define __inline inline -#define noinline __attribute__((noinline)) +#define noinline __attribute__((__noinline__)) #ifndef __always_inline -#define __always_inline inline __attribute__((always_inline)) +#define __always_inline inline __attribute__((__always_inline__)) #endif /* From c2c640aa04cc4e6caf0ff17ff18b3784e0c99566 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Thu, 30 Aug 2018 19:45:01 +0200 Subject: [PATCH 03/17] Compiler Attributes: remove unneeded tests Attributes const and always_inline have tests around them which are unneeded, since they are supported by gcc >= 4.6, clang >= 3 and icc >= 13. https://godbolt.org/z/DFPq37 In the case of gnu_inline, we do not need to test for __GNUC_STDC_INLINE__ because, regardless of the current inlining behavior, we can simply always force the old GCC inlining behavior by using the attribute in all cases. Tested-by: Sedat Dilek # on top of v4.19-rc5, clang 7 Reviewed-by: Nick Desaulniers Reviewed-by: Luc Van Oostenryck Signed-off-by: Miguel Ojeda --- include/linux/compiler_types.h | 23 +++-------------------- 1 file changed, 3 insertions(+), 20 deletions(-) diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index 8fbdd47dd3d0..5ff9cda893f4 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -158,10 +158,6 @@ struct ftrace_likely_data { (sizeof(t) == sizeof(char) || sizeof(t) == sizeof(short) || \ sizeof(t) == sizeof(int) || sizeof(t) == sizeof(long)) -#ifndef __attribute_const__ -#define __attribute_const__ __attribute__((__const__)) -#endif - #ifndef __noclone #define __noclone #endif @@ -196,6 +192,7 @@ struct ftrace_likely_data { * [...] */ #define __pure __attribute__((__pure__)) +#define __attribute_const__ __attribute__((__const__)) #define __aligned(x) __attribute__((__aligned__(x))) #define __aligned_largest __attribute__((__aligned__)) #define __printf(a, b) __attribute__((__format__(printf, a, b))) @@ -211,6 +208,8 @@ struct ftrace_likely_data { #define __alias(symbol) __attribute__((__alias__(#symbol))) #define __cold __attribute__((__cold__)) #define __section(S) __attribute__((__section__(#S))) +#define __always_inline inline __attribute__((__always_inline__)) +#define __gnu_inline __attribute__((__gnu_inline__)) #ifdef CONFIG_ENABLE_MUST_CHECK @@ -235,18 +234,6 @@ struct ftrace_likely_data { #define __compiler_offsetof(a, b) __builtin_offsetof(a, b) -/* - * Feature detection for gnu_inline (gnu89 extern inline semantics). Either - * __GNUC_STDC_INLINE__ is defined (not using gnu89 extern inline semantics, - * and we opt in to the gnu89 semantics), or __GNUC_STDC_INLINE__ is not - * defined so the gnu89 semantics are the default. - */ -#ifdef __GNUC_STDC_INLINE__ -# define __gnu_inline __attribute__((__gnu_inline__)) -#else -# define __gnu_inline -#endif - /* * Force always-inline if the user requests it so via the .config. * GCC does not warn about unused static inline functions for @@ -271,10 +258,6 @@ struct ftrace_likely_data { #define __inline inline #define noinline __attribute__((__noinline__)) -#ifndef __always_inline -#define __always_inline inline __attribute__((__always_inline__)) -#endif - /* * Rather then using noinline to prevent stack consumption, use * noinline_for_stack instead. For documentation reasons. From ec0bbef66f867854691d5af18c2231d746958e0e Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Thu, 30 Aug 2018 19:25:14 +0200 Subject: [PATCH 04/17] Compiler Attributes: homogenize __must_be_array Different definitions of __must_be_array: * gcc: disabled for __CHECKER__ * clang: same definition as gcc's, but without __CHECKER__ * intel: the comment claims __builtin_types_compatible_p() is unsupported; but icc seems to support it since 13.0.1 (released in 2012). See https://godbolt.org/z/S0l6QQ Therefore, we can remove all of them and have a single definition in compiler.h Tested-by: Sedat Dilek # on top of v4.19-rc5, clang 7 Reviewed-by: Nick Desaulniers Reviewed-by: Luc Van Oostenryck Signed-off-by: Miguel Ojeda --- include/linux/compiler-clang.h | 1 - include/linux/compiler-gcc.h | 7 ------- include/linux/compiler-intel.h | 3 --- include/linux/compiler.h | 7 +++++++ 4 files changed, 7 insertions(+), 11 deletions(-) diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h index d11cad61ba5c..fa9532f8d885 100644 --- a/include/linux/compiler-clang.h +++ b/include/linux/compiler-clang.h @@ -41,6 +41,5 @@ * compilers, like ICC. */ #define barrier() __asm__ __volatile__("" : : : "memory") -#define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0])) #define __assume_aligned(a, ...) \ __attribute__((__assume_aligned__(a, ## __VA_ARGS__))) diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h index 7a1de7683df5..3b32bbfa5a49 100644 --- a/include/linux/compiler-gcc.h +++ b/include/linux/compiler-gcc.h @@ -68,13 +68,6 @@ */ #define uninitialized_var(x) x = x -#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 - #ifdef RETPOLINE #define __noretpoline __attribute__((__indirect_branch__("keep"))) #endif diff --git a/include/linux/compiler-intel.h b/include/linux/compiler-intel.h index fef8bb3e53ef..6004b4588bd4 100644 --- a/include/linux/compiler-intel.h +++ b/include/linux/compiler-intel.h @@ -29,9 +29,6 @@ */ #define OPTIMIZER_HIDE_VAR(var) barrier() -/* Intel ECC compiler doesn't support __builtin_types_compatible_p() */ -#define __must_be_array(a) 0 - #endif /* icc has this, but it's called _bswap16 */ diff --git a/include/linux/compiler.h b/include/linux/compiler.h index ec4a28bad2c6..165b1d5683ed 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -357,4 +357,11 @@ static inline void *offset_to_ptr(const int *off) compiletime_assert(__native_word(t), \ "Need native word sized stores/loads for atomicity.") +#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 + #endif /* __LINUX_COMPILER_H */ From 989bd5000f36052df604888ed12bb6ef390786b7 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Fri, 31 Aug 2018 18:00:16 +0200 Subject: [PATCH 05/17] Compiler Attributes: remove unneeded sparse (__CHECKER__) tests Sparse knows about a few more attributes now, so we can remove the __CHECKER__ conditions from them (which, in turn, allow us to move some of them later on to compiler_attributes.h). * assume_aligned: since sparse's commit ffc860b ("sparse: ignore __assume_aligned__ attribute"), included in 0.5.1 * error: since sparse's commit 0a04210 ("sparse: Add 'error' to ignored attributes"), included in 0.5.0 * hotpatch: since sparse's commit 6043210 ("sparse/parse.c: ignore hotpatch attribute"), included in 0.5.1 * warning: since sparse's commit 977365d ("Avoid "attribute 'warning': unknown attribute" warning"), included in 0.4.2 On top of that, __must_be_array does not need it either because: * Even ancient versions of sparse do not have a problem * BUILD_BUG_ON_ZERO() is currently disabled for __CHECKER__ Tested-by: Sedat Dilek # on top of v4.19-rc5, clang 7 Reviewed-by: Nick Desaulniers Reviewed-by: Luc Van Oostenryck Signed-off-by: Miguel Ojeda --- include/linux/compiler-gcc.h | 6 ++---- include/linux/compiler.h | 4 ---- include/linux/compiler_types.h | 2 +- 3 files changed, 3 insertions(+), 9 deletions(-) diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h index 3b32bbfa5a49..1ca6a51cfaa9 100644 --- a/include/linux/compiler-gcc.h +++ b/include/linux/compiler-gcc.h @@ -76,14 +76,12 @@ #define __compiletime_object_size(obj) __builtin_object_size(obj, 0) -#ifndef __CHECKER__ #define __compiletime_warning(message) __attribute__((__warning__(message))) #define __compiletime_error(message) __attribute__((__error__(message))) -#ifdef LATENT_ENTROPY_PLUGIN +#if defined(LATENT_ENTROPY_PLUGIN) && !defined(__CHECKER__) #define __latent_entropy __attribute__((latent_entropy)) #endif -#endif /* __CHECKER__ */ /* * calling noreturn functions, __builtin_unreachable() and __builtin_trap() @@ -131,7 +129,7 @@ /* gcc version specific checks */ -#if GCC_VERSION >= 40900 && !defined(__CHECKER__) +#if GCC_VERSION >= 40900 /* * __assume_aligned(n, k): Tell the optimizer that the returned * pointer can be assumed to be k modulo n. The second argument is diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 165b1d5683ed..4030a2940d6b 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -357,11 +357,7 @@ static inline void *offset_to_ptr(const int *off) compiletime_assert(__native_word(t), \ "Need native word sized stores/loads for atomicity.") -#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 #endif /* __LINUX_COMPILER_H */ diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index 5ff9cda893f4..a3eceb3ad1b3 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -218,7 +218,7 @@ struct ftrace_likely_data { #define __must_check #endif -#if defined(CC_USING_HOTPATCH) && !defined(__CHECKER__) +#if defined(CC_USING_HOTPATCH) #define notrace __attribute__((hotpatch(0, 0))) #else #define notrace __attribute__((__no_instrument_function__)) From 66dbeef915f275dad6c8656b31667ef9640f5639 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Mon, 3 Sep 2018 18:34:18 +0200 Subject: [PATCH 06/17] Compiler Attributes: add missing SPDX ID in compiler_types.h Tested-by: Sedat Dilek # on top of v4.19-rc5, clang 7 Reviewed-by: Nick Desaulniers Reviewed-by: Luc Van Oostenryck Signed-off-by: Miguel Ojeda --- include/linux/compiler_types.h | 1 + 1 file changed, 1 insertion(+) diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index a3eceb3ad1b3..ed7c0e4a180e 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -1,3 +1,4 @@ +/* SPDX-License-Identifier: GPL-2.0 */ #ifndef __LINUX_COMPILER_TYPES_H #define __LINUX_COMPILER_TYPES_H From a3f8a30f3f0079c7edfc72e329eee8594fb3e3cb Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Thu, 30 Aug 2018 20:36:59 +0200 Subject: [PATCH 07/17] Compiler Attributes: use feature checks instead of version checks Instead of using version checks per-compiler to define (or not) each attribute, use __has_attribute to test for them, following the cleanup started with commit 815f0ddb346c ("include/linux/compiler*.h: make compiler-*.h mutually exclusive"), which is supported on gcc >= 5, clang >= 2.9 and icc >= 17. In the meantime, to support 4.6 <= gcc < 5, we implement __has_attribute by hand. All the attributes that can be unconditionally defined and directly map to compiler attribute(s) (even if optional) have been moved to a new file include/linux/compiler_attributes.h In an effort to make the file as regular as possible, comments stating the purpose of attributes have been removed. Instead, links to the compiler docs have been added (i.e. to gcc and, if available, to clang as well). In addition, they have been sorted. Finally, if an attribute is optional (i.e. if it is guarded by __has_attribute), the reason has been stated for future reference. Tested-by: Sedat Dilek # on top of v4.19-rc5, clang 7 Reviewed-by: Nick Desaulniers Reviewed-by: Luc Van Oostenryck Signed-off-by: Miguel Ojeda --- include/linux/compiler-clang.h | 4 - include/linux/compiler-gcc.h | 51 ------ include/linux/compiler-intel.h | 6 - include/linux/compiler_attributes.h | 244 ++++++++++++++++++++++++++++ include/linux/compiler_types.h | 74 ++------- 5 files changed, 254 insertions(+), 125 deletions(-) create mode 100644 include/linux/compiler_attributes.h diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h index fa9532f8d885..3e7dafb3ea80 100644 --- a/include/linux/compiler-clang.h +++ b/include/linux/compiler-clang.h @@ -21,8 +21,6 @@ #define __SANITIZE_ADDRESS__ #endif -#define __no_sanitize_address __attribute__((__no_sanitize__("address"))) - /* * Not all versions of clang implement the the type-generic versions * of the builtin overflow checkers. Fortunately, clang implements @@ -41,5 +39,3 @@ * compilers, like ICC. */ #define barrier() __asm__ __volatile__("" : : : "memory") -#define __assume_aligned(a, ...) \ - __attribute__((__assume_aligned__(a, ## __VA_ARGS__))) diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h index 1ca6a51cfaa9..cfac027e1625 100644 --- a/include/linux/compiler-gcc.h +++ b/include/linux/compiler-gcc.h @@ -108,9 +108,6 @@ __builtin_unreachable(); \ } while (0) -/* Mark a function definition as prohibited from being cloned. */ -#define __noclone __attribute__((__noclone__, __optimize__("no-tracer"))) - #if defined(RANDSTRUCT_PLUGIN) && !defined(__CHECKER__) #define __randomize_layout __attribute__((randomize_layout)) #define __no_randomize_layout __attribute__((no_randomize_layout)) @@ -119,32 +116,6 @@ #define randomized_struct_fields_end } __randomize_layout; #endif -/* - * 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__)) - -/* gcc version specific checks */ - -#if GCC_VERSION >= 40900 -/* - * __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: * @@ -176,32 +147,10 @@ #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 - #if GCC_VERSION >= 50100 -/* - * Mark structures as requiring designated initializers. - * https://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html - */ -#define __designated_init __attribute__((__designated_init__)) #define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1 #endif -#if !defined(__noclone) -#define __noclone /* not needed */ -#endif - -#if !defined(__no_sanitize_address) -#define __no_sanitize_address -#endif - /* * Turn individual warnings and errors on and off locally, depending * on version. diff --git a/include/linux/compiler-intel.h b/include/linux/compiler-intel.h index 6004b4588bd4..517bd14e1222 100644 --- a/include/linux/compiler-intel.h +++ b/include/linux/compiler-intel.h @@ -34,9 +34,3 @@ /* icc has this, but it's called _bswap16 */ #define __HAVE_BUILTIN_BSWAP16__ #define __builtin_bswap16 _bswap16 - -/* The following are for compatibility with GCC, from compiler-gcc.h, - * and may be redefined here because they should not be shared with other - * compilers, like clang. - */ -#define __visible __attribute__((__externally_visible__)) diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h new file mode 100644 index 000000000000..f0f9fc398440 --- /dev/null +++ b/include/linux/compiler_attributes.h @@ -0,0 +1,244 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef __LINUX_COMPILER_ATTRIBUTES_H +#define __LINUX_COMPILER_ATTRIBUTES_H + +/* + * The attributes in this file are unconditionally defined and they directly + * map to compiler attribute(s) -- except those that are optional. + * + * Any other "attributes" (i.e. those that depend on a configuration option, + * on a compiler, on an architecture, on plugins, on other attributes...) + * should be defined elsewhere (e.g. compiler_types.h or compiler-*.h). + * + * This file is meant to be sorted (by actual attribute name, + * not by #define identifier). Use the __attribute__((__name__)) syntax + * (i.e. with underscores) to avoid future collisions with other macros. + * If an attribute is optional, state the reason in the comment. + */ + +/* + * To check for optional attributes, we use __has_attribute, which is supported + * on gcc >= 5, clang >= 2.9 and icc >= 17. In the meantime, to support + * 4.6 <= gcc < 5, we implement __has_attribute by hand. + * + * sparse does not support __has_attribute (yet) and defines __GNUC_MINOR__ + * depending on the compiler used to build it; however, these attributes have + * no semantic effects for sparse, so it does not matter. Also note that, + * in order to avoid sparse's warnings, even the unsupported ones must be + * defined to 0. + */ +#ifndef __has_attribute +# define __has_attribute(x) __GCC4_has_attribute_##x +# define __GCC4_has_attribute___assume_aligned__ (__GNUC_MINOR__ >= 9) +# define __GCC4_has_attribute___designated_init__ 0 +# define __GCC4_has_attribute___externally_visible__ 1 +# define __GCC4_has_attribute___noclone__ 1 +# define __GCC4_has_attribute___optimize__ 1 +# define __GCC4_has_attribute___no_sanitize_address__ (__GNUC_MINOR__ >= 8) +#endif + +/* + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-alias-function-attribute + */ +#define __alias(symbol) __attribute__((__alias__(#symbol))) + +/* + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-aligned-function-attribute + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-aligned-type-attribute + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-aligned-variable-attribute + */ +#define __aligned(x) __attribute__((__aligned__(x))) +#define __aligned_largest __attribute__((__aligned__)) + +/* + * Note: users of __always_inline currently do not write "inline" themselves, + * which seems to be required by gcc to apply the attribute according + * to its docs (and also "warning: always_inline function might not be + * inlinable [-Wattributes]" is emitted). + * + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-always_005finline-function-attribute + * clang: mentioned + */ +#define __always_inline inline __attribute__((__always_inline__)) + +/* + * 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;'). + * + * Optional: only supported since gcc >= 4.9 + * Optional: not supported by icc + * + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-assume_005faligned-function-attribute + * clang: https://clang.llvm.org/docs/AttributeReference.html#assume-aligned + */ +#if __has_attribute(__assume_aligned__) +# define __assume_aligned(a, ...) __attribute__((__assume_aligned__(a, ## __VA_ARGS__))) +#else +# define __assume_aligned(a, ...) +#endif + +/* + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-cold-function-attribute + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Label-Attributes.html#index-cold-label-attribute + */ +#define __cold __attribute__((__cold__)) + +/* + * Note the long name. + * + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-const-function-attribute + */ +#define __attribute_const__ __attribute__((__const__)) + +/* + * Don't. Just don't. See commit 771c035372a0 ("deprecate the '__deprecated' + * attribute warnings entirely and for good") for more information. + * + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-deprecated-function-attribute + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-deprecated-type-attribute + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-deprecated-variable-attribute + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Enumerator-Attributes.html#index-deprecated-enumerator-attribute + * clang: https://clang.llvm.org/docs/AttributeReference.html#deprecated + */ +#define __deprecated + +/* + * Optional: only supported since gcc >= 5.1 + * Optional: not supported by clang + * Optional: not supported by icc + * + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-designated_005finit-type-attribute + */ +#if __has_attribute(__designated_init__) +# define __designated_init __attribute__((__designated_init__)) +#else +# define __designated_init +#endif + +/* + * Optional: not supported by clang + * + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-externally_005fvisible-function-attribute + */ +#if __has_attribute(__externally_visible__) +# define __visible __attribute__((__externally_visible__)) +#else +# define __visible +#endif + +/* + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-format-function-attribute + * clang: https://clang.llvm.org/docs/AttributeReference.html#format + */ +#define __printf(a, b) __attribute__((__format__(printf, a, b))) +#define __scanf(a, b) __attribute__((__format__(scanf, a, b))) + +/* + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-gnu_005finline-function-attribute + * clang: https://clang.llvm.org/docs/AttributeReference.html#gnu-inline + */ +#define __gnu_inline __attribute__((__gnu_inline__)) + +/* + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-malloc-function-attribute + */ +#define __malloc __attribute__((__malloc__)) + +/* + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-mode-type-attribute + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-mode-variable-attribute + */ +#define __mode(x) __attribute__((__mode__(x))) + +/* + * Optional: not supported by clang + * Note: icc does not recognize gcc's no-tracer + * + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noclone-function-attribute + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-optimize-function-attribute + */ +#if __has_attribute(__noclone__) +# if __has_attribute(__optimize__) +# define __noclone __attribute__((__noclone__, __optimize__("no-tracer"))) +# else +# define __noclone __attribute__((__noclone__)) +# endif +#else +# define __noclone +#endif + +/* + * Note the missing underscores. + * + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noinline-function-attribute + * clang: mentioned + */ +#define noinline __attribute__((__noinline__)) + +/* + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noreturn-function-attribute + * clang: https://clang.llvm.org/docs/AttributeReference.html#noreturn + * clang: https://clang.llvm.org/docs/AttributeReference.html#id1 + */ +#define __noreturn __attribute__((__noreturn__)) + +/* + * Optional: only supported since gcc >= 4.8 + * Optional: not supported by icc + * + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-no_005fsanitize_005faddress-function-attribute + * clang: https://clang.llvm.org/docs/AttributeReference.html#no-sanitize-address-no-address-safety-analysis + */ +#if __has_attribute(__no_sanitize_address__) +# define __no_sanitize_address __attribute__((__no_sanitize_address__)) +#else +# define __no_sanitize_address +#endif + +/* + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-packed-type-attribute + * clang: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-packed-variable-attribute + */ +#define __packed __attribute__((__packed__)) + +/* + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-pure-function-attribute + */ +#define __pure __attribute__((__pure__)) + +/* + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-section-function-attribute + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-section-variable-attribute + * clang: https://clang.llvm.org/docs/AttributeReference.html#section-declspec-allocate + */ +#define __section(S) __attribute__((__section__(#S))) + +/* + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-unused-function-attribute + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-unused-type-attribute + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-unused-variable-attribute + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Label-Attributes.html#index-unused-label-attribute + * clang: https://clang.llvm.org/docs/AttributeReference.html#maybe-unused-unused + */ +#define __always_unused __attribute__((__unused__)) +#define __maybe_unused __attribute__((__unused__)) + +/* + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-used-function-attribute + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-used-variable-attribute + */ +#define __used __attribute__((__used__)) + +/* + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-weak-function-attribute + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-weak-variable-attribute + */ +#define __weak __attribute__((__weak__)) + +#endif /* __LINUX_COMPILER_ATTRIBUTES_H */ diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index ed7c0e4a180e..3439d7d0249a 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -55,6 +55,9 @@ extern void __chk_io_ptr(const volatile void __iomem *); #ifdef __KERNEL__ +/* Attributes */ +#include + /* Compiler specific macros. */ #ifdef __clang__ #include @@ -79,12 +82,6 @@ extern void __chk_io_ptr(const volatile void __iomem *); #include #endif -/* - * Generic compiler-independent macros required for kernel - * build go below this comment. Actual compiler/compiler version - * specific implementations come from the above header files - */ - struct ftrace_branch_data { const char *func; const char *file; @@ -107,9 +104,6 @@ struct ftrace_likely_data { unsigned long constant; }; -/* Don't. Just don't. */ -#define __deprecated - #endif /* __KERNEL__ */ #endif /* __ASSEMBLY__ */ @@ -119,10 +113,6 @@ struct ftrace_likely_data { * compilers. We don't consider that to be an error, so set them to nothing. * For example, some of them are for compiler specific plugins. */ -#ifndef __designated_init -# define __designated_init -#endif - #ifndef __latent_entropy # define __latent_entropy #endif @@ -140,17 +130,6 @@ struct ftrace_likely_data { # define randomized_struct_fields_end #endif -#ifndef __visible -#define __visible -#endif - -/* - * Assume alignment of return value. - */ -#ifndef __assume_aligned -#define __assume_aligned(a, ...) -#endif - /* Are two types/vars the same type (ignoring qualifiers)? */ #define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b)) @@ -159,10 +138,6 @@ struct ftrace_likely_data { (sizeof(t) == sizeof(char) || sizeof(t) == sizeof(short) || \ sizeof(t) == sizeof(int) || sizeof(t) == sizeof(long)) -#ifndef __noclone -#define __noclone -#endif - /* Helpers for emitting diagnostics in pragmas. */ #ifndef __diag #define __diag(string) @@ -182,37 +157,6 @@ struct ftrace_likely_data { #define __diag_error(compiler, version, option, comment) \ __diag_ ## compiler(version, error, option) -/* - * 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 __attribute_const__ __attribute__((__const__)) -#define __aligned(x) __attribute__((__aligned__(x))) -#define __aligned_largest __attribute__((__aligned__)) -#define __printf(a, b) __attribute__((__format__(printf, a, b))) -#define __scanf(a, b) __attribute__((__format__(scanf, a, b))) -#define __maybe_unused __attribute__((__unused__)) -#define __always_unused __attribute__((__unused__)) -#define __mode(x) __attribute__((__mode__(x))) -#define __malloc __attribute__((__malloc__)) -#define __used __attribute__((__used__)) -#define __noreturn __attribute__((__noreturn__)) -#define __packed __attribute__((__packed__)) -#define __weak __attribute__((__weak__)) -#define __alias(symbol) __attribute__((__alias__(#symbol))) -#define __cold __attribute__((__cold__)) -#define __section(S) __attribute__((__section__(#S))) -#define __always_inline inline __attribute__((__always_inline__)) -#define __gnu_inline __attribute__((__gnu_inline__)) - - #ifdef CONFIG_ENABLE_MUST_CHECK #define __must_check __attribute__((__warn_unused_result__)) #else @@ -246,18 +190,20 @@ struct ftrace_likely_data { * semantics rather than c99. This prevents multiple symbol definition errors * of extern inline functions at link time. * A lot of inline functions can cause havoc with function tracing. + * Do not use __always_inline here, since currently it expands to inline again + * (which would break users of __always_inline). */ #if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) || \ !defined(CONFIG_OPTIMIZE_INLINING) -#define inline \ - inline __attribute__((__always_inline__, __unused__)) notrace __gnu_inline +#define inline inline __attribute__((__always_inline__)) __gnu_inline \ + __maybe_unused notrace #else -#define inline inline __attribute__((__unused__)) notrace __gnu_inline +#define inline inline __gnu_inline \ + __maybe_unused notrace #endif #define __inline__ inline -#define __inline inline -#define noinline __attribute__((__noinline__)) +#define __inline inline /* * Rather then using noinline to prevent stack consumption, use From 06e3727e02f9ee9cf571692cd5c74fc5a8a2af52 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Mon, 3 Sep 2018 19:22:13 +0200 Subject: [PATCH 08/17] Compiler Attributes: KENTRY used twice the "used" attribute Tested-by: Sedat Dilek # on top of v4.19-rc5, clang 7 Reviewed-by: Nick Desaulniers Reviewed-by: Luc Van Oostenryck Signed-off-by: Miguel Ojeda --- include/linux/compiler.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 4030a2940d6b..17ee9165ca51 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -146,7 +146,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, extern typeof(sym) sym; \ static const unsigned long __kentry_##sym \ __used \ - __attribute__((__section__("___kentry" "+" #sym ), used)) \ + __attribute__((__section__("___kentry" "+" #sym ))) \ = (unsigned long)&sym; #endif From e04462fb82f8dd98288c0e7ab1eec79c92537d25 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Mon, 3 Sep 2018 19:17:50 +0200 Subject: [PATCH 09/17] Compiler Attributes: remove uses of __attribute__ from compiler.h Suggested-by: Nick Desaulniers Tested-by: Sedat Dilek # on top of v4.19-rc5, clang 7 Reviewed-by: Nick Desaulniers Reviewed-by: Luc Van Oostenryck Signed-off-by: Miguel Ojeda --- include/linux/compiler.h | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 17ee9165ca51..b5fb034fa6fa 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -23,8 +23,8 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, #define __branch_check__(x, expect, is_constant) ({ \ long ______r; \ static struct ftrace_likely_data \ - __attribute__((__aligned__(4))) \ - __attribute__((__section__("_ftrace_annotated_branch"))) \ + __aligned(4) \ + __section("_ftrace_annotated_branch") \ ______f = { \ .data.func = __func__, \ .data.file = __FILE__, \ @@ -59,8 +59,8 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, ({ \ int ______r; \ static struct ftrace_branch_data \ - __attribute__((__aligned__(4))) \ - __attribute__((__section__("_ftrace_branch"))) \ + __aligned(4) \ + __section("_ftrace_branch") \ ______f = { \ .func = __func__, \ .file = __FILE__, \ @@ -146,7 +146,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, extern typeof(sym) sym; \ static const unsigned long __kentry_##sym \ __used \ - __attribute__((__section__("___kentry" "+" #sym ))) \ + __section("___kentry" "+" #sym ) \ = (unsigned long)&sym; #endif @@ -287,7 +287,7 @@ unsigned long read_word_at_a_time(const void *addr) * visible to the compiler. */ #define __ADDRESSABLE(sym) \ - static void * __attribute__((__section__(".discard.addressable"), used)) \ + static void * __section(".discard.addressable") __used \ __PASTE(__addressable_##sym, __LINE__) = (void *)&sym; /** From 303d22c5fc37cebe2bd0b3c15ac3db6950db60c6 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Mon, 3 Sep 2018 18:32:11 +0200 Subject: [PATCH 10/17] Compiler Attributes: add Doc/process/programming-language.rst Tested-by: Sedat Dilek # on top of v4.19-rc5, clang 7 Reviewed-by: Nick Desaulniers Reviewed-by: Luc Van Oostenryck Signed-off-by: Miguel Ojeda --- Documentation/process/index.rst | 1 + .../process/programming-language.rst | 45 +++++++++++++++++++ 2 files changed, 46 insertions(+) create mode 100644 Documentation/process/programming-language.rst diff --git a/Documentation/process/index.rst b/Documentation/process/index.rst index 9ae3e317bddf..00558b6d2649 100644 --- a/Documentation/process/index.rst +++ b/Documentation/process/index.rst @@ -23,6 +23,7 @@ Below are the essential guides that every developer should read. code-of-conduct development-process submitting-patches + programming-language coding-style maintainer-pgp-guide email-clients diff --git a/Documentation/process/programming-language.rst b/Documentation/process/programming-language.rst new file mode 100644 index 000000000000..e5f5f065dc24 --- /dev/null +++ b/Documentation/process/programming-language.rst @@ -0,0 +1,45 @@ +.. _programming_language: + +Programming Language +==================== + +The kernel is written in the C programming language [c-language]_. +More precisely, the kernel is typically compiled with ``gcc`` [gcc]_ +under ``-std=gnu89`` [gcc-c-dialect-options]_: the GNU dialect of ISO C90 +(including some C99 features). + +This dialect contains many extensions to the language [gnu-extensions]_, +and many of them are used within the kernel as a matter of course. + +There is some support for compiling the kernel with ``clang`` [clang]_ +and ``icc`` [icc]_ for several of the architectures, although at the time +of writing it is not completed, requiring third-party patches. + +Attributes +---------- + +One of the common extensions used throughout the kernel are attributes +[gcc-attribute-syntax]_. Attributes allow to introduce +implementation-defined semantics to language entities (like variables, +functions or types) without having to make significant syntactic changes +to the language (e.g. adding a new keyword) [n2049]_. + +In some cases, attributes are optional (i.e. a compiler not supporting them +should still produce proper code, even if it is slower or does not perform +as many compile-time checks/diagnostics). + +The kernel defines pseudo-keywords (e.g. ``__pure``) instead of using +directly the GNU attribute syntax (e.g. ``__attribute__((__pure__))``) +in order to feature detect which ones can be used and/or to shorten the code. + +Please refer to ``include/linux/compiler_attributes.h`` for more information. + +.. [c-language] http://www.open-std.org/jtc1/sc22/wg14/www/standards +.. [gcc] https://gcc.gnu.org +.. [clang] https://clang.llvm.org +.. [icc] https://software.intel.com/en-us/c-compilers +.. [gcc-c-dialect-options] https://gcc.gnu.org/onlinedocs/gcc/C-Dialect-Options.html +.. [gnu-extensions] https://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html +.. [gcc-attribute-syntax] https://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html +.. [n2049] http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2049.pdf + From 5fc4a13b66b4643b7a564cc79c2453889c8665d7 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Sat, 8 Sep 2018 22:53:57 +0200 Subject: [PATCH 11/17] Compiler Attributes: add MAINTAINERS entry Tested-by: Sedat Dilek # on top of v4.19-rc5, clang 7 Reviewed-by: Nick Desaulniers Reviewed-by: Luc Van Oostenryck Signed-off-by: Miguel Ojeda --- MAINTAINERS | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/MAINTAINERS b/MAINTAINERS index b22e7fdfd2ea..e4980d675584 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -3722,6 +3722,11 @@ L: platform-driver-x86@vger.kernel.org S: Maintained F: drivers/platform/x86/compal-laptop.c +COMPILER ATTRIBUTES +M: Miguel Ojeda +S: Maintained +F: include/linux/compiler_attributes.h + CONEXANT ACCESSRUNNER USB DRIVER L: accessrunner-general@lists.sourceforge.net W: http://accessrunner.sourceforge.net/ From 92676236917d8e2e0de1d8612686d3d04a6a245b Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Wed, 19 Sep 2018 01:06:24 +0200 Subject: [PATCH 12/17] Compiler Attributes: add support for __nonstring (gcc >= 8) From the GCC manual: nonstring The nonstring variable attribute specifies that an object or member declaration with type array of char, signed char, or unsigned char, or pointer to such a type is intended to store character arrays that do not necessarily contain a terminating NUL. This is useful in detecting uses of such arrays or pointers with functions that expect NUL-terminated strings, and to avoid warnings when such an array or pointer is used as an argument to a bounded string manipulation function such as strncpy. https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html This attribute can be used for documentation purposes (i.e. replacing comments), but it is most helpful when the following warnings are enabled: -Wstringop-overflow Warn for calls to string manipulation functions such as memcpy and strcpy that are determined to overflow the destination buffer. [...] -Wstringop-truncation Warn for calls to bounded string manipulation functions such as strncat, strncpy, and stpncpy that may either truncate the copied string or leave the destination unchanged. [...] In situations where a character array is intended to store a sequence of bytes with no terminating NUL such an array may be annotated with attribute nonstring to avoid this warning. Such arrays, however, are not suitable arguments to functions that expect NUL-terminated strings. To help detect accidental misuses of such arrays GCC issues warnings unless it can prove that the use is safe. https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html Tested-by: Sedat Dilek # on top of v4.19-rc5, clang 7 Reviewed-by: Kees Cook Reviewed-by: Nick Desaulniers Reviewed-by: Luc Van Oostenryck Signed-off-by: Miguel Ojeda --- include/linux/compiler_attributes.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h index f0f9fc398440..6b28c1b7310c 100644 --- a/include/linux/compiler_attributes.h +++ b/include/linux/compiler_attributes.h @@ -34,6 +34,7 @@ # define __GCC4_has_attribute___externally_visible__ 1 # define __GCC4_has_attribute___noclone__ 1 # define __GCC4_has_attribute___optimize__ 1 +# define __GCC4_has_attribute___nonstring__ 0 # define __GCC4_has_attribute___no_sanitize_address__ (__GNUC_MINOR__ >= 8) #endif @@ -181,6 +182,19 @@ */ #define noinline __attribute__((__noinline__)) +/* + * Optional: only supported since gcc >= 8 + * Optional: not supported by clang + * Optional: not supported by icc + * + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-nonstring-variable-attribute + */ +#if __has_attribute(__nonstring__) +# define __nonstring __attribute__((__nonstring__)) +#else +# define __nonstring +#endif + /* * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noreturn-function-attribute * clang: https://clang.llvm.org/docs/AttributeReference.html#noreturn From 23066c3f4e2146da8c7d1505729f4409f4d93d28 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Wed, 19 Sep 2018 02:31:58 +0200 Subject: [PATCH 13/17] Compiler Attributes: enable -Wstringop-truncation on W=1 (gcc >= 8) Commit 217c3e019675 ("disable stringop truncation warnings for now") disabled -Wstringop-truncation since it was too noisy. Having __nonstring available allows us to let GCC know that a string is not meant to be NUL-terminated, which helps suppressing some -Wstringop-truncation warnings. Note that using __nonstring actually triggers other warnings (-Wstringop-overflow, which is on by default) which may be real problems. Therefore, cleaning up -Wstringop-truncation warnings also buys us the ability to uncover further potential problems. To encourage the use of __nonstring, we put the warning back at W=1. In the future, if we end up with a fairly warning-free tree, we might want to enable it by default. Tested-by: Sedat Dilek # on top of v4.19-rc5, clang 7 Reviewed-by: Kees Cook Reviewed-by: Nick Desaulniers Reviewed-by: Luc Van Oostenryck Signed-off-by: Miguel Ojeda --- scripts/Makefile.extrawarn | 1 + 1 file changed, 1 insertion(+) diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn index 8d5357053f86..b8f36f5f43f2 100644 --- a/scripts/Makefile.extrawarn +++ b/scripts/Makefile.extrawarn @@ -29,6 +29,7 @@ warning-1 += $(call cc-option, -Wmissing-include-dirs) warning-1 += $(call cc-option, -Wunused-but-set-variable) warning-1 += $(call cc-option, -Wunused-const-variable) warning-1 += $(call cc-option, -Wpacked-not-aligned) +warning-1 += $(call cc-option, -Wstringop-truncation) warning-1 += $(call cc-disable-warning, missing-field-initializers) warning-1 += $(call cc-disable-warning, sign-compare) From 98cade0a08ba339cd11d6e89b0df5d1d2fa21202 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Tue, 14 Aug 2018 21:38:26 +0200 Subject: [PATCH 14/17] Compiler Attributes: auxdisplay: panel: use __nonstring Let gcc know these arrays are not meant to be NUL-terminated by annotating them with the new __nonstring variable attribute; and remove the comment since it conveys the same information. Tested-by: Sedat Dilek # on top of v4.19-rc5, clang 7 Reviewed-by: Nick Desaulniers Reviewed-by: Luc Van Oostenryck Signed-off-by: Miguel Ojeda --- drivers/auxdisplay/panel.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/drivers/auxdisplay/panel.c b/drivers/auxdisplay/panel.c index 3b25a643058c..21b9b2f2470a 100644 --- a/drivers/auxdisplay/panel.c +++ b/drivers/auxdisplay/panel.c @@ -155,10 +155,9 @@ struct logical_input { int release_data; } std; struct { /* valid when type == INPUT_TYPE_KBD */ - /* strings can be non null-terminated */ - char press_str[sizeof(void *) + sizeof(int)]; - char repeat_str[sizeof(void *) + sizeof(int)]; - char release_str[sizeof(void *) + sizeof(int)]; + char press_str[sizeof(void *) + sizeof(int)] __nonstring; + char repeat_str[sizeof(void *) + sizeof(int)] __nonstring; + char release_str[sizeof(void *) + sizeof(int)] __nonstring; } kbd; } u; }; From f0604f63033d4020f019d2aaee805c1075b1077b Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Wed, 19 Sep 2018 01:41:21 +0200 Subject: [PATCH 15/17] Compiler Attributes: ext4: remove local __nonstring definition Commit 072ebb3bffe6 ("ext4: add nonstring annotations to ext4.h") introduced a local definition of __nonstring to suppress some false positives in gcc 8's -Wstringop-truncation. Since now we support __nonstring for everyone, remove it. Tested-by: Sedat Dilek # on top of v4.19-rc5, clang 7 Reviewed-by: Nick Desaulniers Reviewed-by: Luc Van Oostenryck Signed-off-by: Miguel Ojeda --- fs/ext4/ext4.h | 9 --------- 1 file changed, 9 deletions(-) diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index caff935fbeb8..2acdfdad3d3f 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -45,15 +45,6 @@ #include -/* Until this gets included into linux/compiler-gcc.h */ -#ifndef __nonstring -#if defined(GCC_VERSION) && (GCC_VERSION >= 80000) -#define __nonstring __attribute__((nonstring)) -#else -#define __nonstring -#endif -#endif - /* * The fourth extended filesystem constants/structures */ From fe0640eb30b7da261ae84d252ed9ed3c7e68dfd8 Mon Sep 17 00:00:00 2001 From: "ndesaulniers@google.com" Date: Mon, 15 Oct 2018 10:22:21 -0700 Subject: [PATCH 16/17] compiler.h: update definition of unreachable() Fixes the objtool warning seen with Clang: arch/x86/mm/fault.o: warning: objtool: no_context()+0x220: unreachable instruction Fixes commit 815f0ddb346c ("include/linux/compiler*.h: make compiler-*.h mutually exclusive") Josh noted that the fallback definition was meant to work around a pre-gcc-4.6 bug. GCC still needs to work around https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82365, so compiler-gcc.h defines its own version of unreachable(). Clang and ICC can use this shared definition. Link: https://github.com/ClangBuiltLinux/linux/issues/204 Suggested-by: Andy Lutomirski Suggested-by: Josh Poimboeuf Tested-by: Nathan Chancellor Signed-off-by: Nick Desaulniers Signed-off-by: Miguel Ojeda --- include/linux/compiler.h | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/include/linux/compiler.h b/include/linux/compiler.h index b5fb034fa6fa..2e0b6322588b 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -124,7 +124,10 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, # define ASM_UNREACHABLE #endif #ifndef unreachable -# define unreachable() do { annotate_reachable(); do { } while (1); } while (0) +# define unreachable() do { \ + annotate_unreachable(); \ + __builtin_unreachable(); \ +} while (0) #endif /* From 1ff2fea5e30ca15752777441ecb64a169fe22e9e Mon Sep 17 00:00:00 2001 From: "ndesaulniers@google.com" Date: Mon, 15 Oct 2018 14:24:27 -0700 Subject: [PATCH 17/17] compiler-gcc: remove comment about gcc 4.5 from unreachable() Remove the comment about being unable to detect __builtin_unreachable. __builtin_unreachable was implemented in the GCC 4.5 timeframe. The kernel's minimum supported version of GCC is 4.6 since commit cafa0010cd51 ("Raise the minimum required gcc version to 4.6"). Commit cb984d101b30 ("compiler-gcc: integrate the various compiler-gcc[345].h files") shows that unreachable() had different guards based on GCC version. Suggested-by: Miguel Ojeda Signed-off-by: Nick Desaulniers Signed-off-by: Miguel Ojeda --- include/linux/compiler-gcc.h | 4 ---- 1 file changed, 4 deletions(-) diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h index cfac027e1625..2010493e1040 100644 --- a/include/linux/compiler-gcc.h +++ b/include/linux/compiler-gcc.h @@ -96,10 +96,6 @@ * 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() \ do { \