diff options
Diffstat (limited to 'include/linux/static_call.h')
| -rw-r--r-- | include/linux/static_call.h | 144 |
1 files changed, 99 insertions, 45 deletions
diff --git a/include/linux/static_call.h b/include/linux/static_call.h index 695da4c9b338..78a77a4ae0ea 100644 --- a/include/linux/static_call.h +++ b/include/linux/static_call.h @@ -17,9 +17,16 @@ * DECLARE_STATIC_CALL(name, func); * DEFINE_STATIC_CALL(name, func); * DEFINE_STATIC_CALL_NULL(name, typename); + * DEFINE_STATIC_CALL_RET0(name, typename); + * + * __static_call_return0; + * * static_call(name)(args...); * static_call_cond(name)(args...); * static_call_update(name, func); + * static_call_query(name); + * + * EXPORT_STATIC_CALL{,_TRAMP}{,_GPL}() * * Usage example: * @@ -91,6 +98,37 @@ * * which will include the required value tests to avoid NULL-pointer * dereferences. + * + * To query which function is currently set to be called, use: + * + * func = static_call_query(name); + * + * + * DEFINE_STATIC_CALL_RET0 / __static_call_return0: + * + * Just like how DEFINE_STATIC_CALL_NULL() / static_call_cond() optimize the + * conditional void function call, DEFINE_STATIC_CALL_RET0 / + * __static_call_return0 optimize the do nothing return 0 function. + * + * This feature is strictly UB per the C standard (since it casts a function + * pointer to a different signature) and relies on the architecture ABI to + * make things work. In particular it relies on Caller Stack-cleanup and the + * whole return register being clobbered for short return values. All normal + * CDECL style ABIs conform. + * + * In particular the x86_64 implementation replaces the 5 byte CALL + * instruction at the callsite with a 5 byte clear of the RAX register, + * completely eliding any function call overhead. + * + * Notably argument setup is unconditional. + * + * + * EXPORT_STATIC_CALL() vs EXPORT_STATIC_CALL_TRAMP(): + * + * The difference is that the _TRAMP variant tries to only export the + * trampoline with the result that a module can use static_call{,_cond}() but + * not static_call_update(). + * */ #include <linux/types.h> @@ -107,57 +145,45 @@ extern void arch_static_call_transform(void *site, void *tramp, void *func, bool #define STATIC_CALL_TRAMP_ADDR(name) &STATIC_CALL_TRAMP(name) -/* - * __ADDRESSABLE() is used to ensure the key symbol doesn't get stripped from - * the symbol table so that objtool can reference it when it generates the - * .static_call_sites section. - */ -#define __static_call(name) \ -({ \ - __ADDRESSABLE(STATIC_CALL_KEY(name)); \ - &STATIC_CALL_TRAMP(name); \ -}) - #else #define STATIC_CALL_TRAMP_ADDR(name) NULL #endif - -#define DECLARE_STATIC_CALL(name, func) \ - extern struct static_call_key STATIC_CALL_KEY(name); \ - extern typeof(func) STATIC_CALL_TRAMP(name); - #define static_call_update(name, func) \ ({ \ - BUILD_BUG_ON(!__same_type(*(func), STATIC_CALL_TRAMP(name))); \ + typeof(&STATIC_CALL_TRAMP(name)) __F = (func); \ __static_call_update(&STATIC_CALL_KEY(name), \ - STATIC_CALL_TRAMP_ADDR(name), func); \ + STATIC_CALL_TRAMP_ADDR(name), __F); \ }) +#define static_call_query(name) (READ_ONCE(STATIC_CALL_KEY(name).func)) + #ifdef CONFIG_HAVE_STATIC_CALL_INLINE +extern int static_call_initialized; + extern int __init static_call_init(void); +extern void static_call_force_reinit(void); + struct static_call_mod { struct static_call_mod *next; struct module *mod; /* for vmlinux, mod == NULL */ struct static_call_site *sites; }; -struct static_call_key { - void *func; - union { - /* bit 0: 0 = mods, 1 = sites */ - unsigned long type; - struct static_call_mod *mods; - struct static_call_site *sites; - }; +/* For finding the key associated with a trampoline */ +struct static_call_tramp_key { + s32 tramp; + s32 key; }; extern void __static_call_update(struct static_call_key *key, void *tramp, void *func); extern int static_call_mod_init(struct module *mod); extern int static_call_text_reserved(void *start, void *end); +extern long __static_call_return0(void); + #define DEFINE_STATIC_CALL(name, _func) \ DECLARE_STATIC_CALL(name, _func); \ struct static_call_key STATIC_CALL_KEY(name) = { \ @@ -174,24 +200,36 @@ extern int static_call_text_reserved(void *start, void *end); }; \ ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name) -#define static_call(name) __static_call(name) +#define DEFINE_STATIC_CALL_RET0(name, _func) \ + DECLARE_STATIC_CALL(name, _func); \ + struct static_call_key STATIC_CALL_KEY(name) = { \ + .func = __static_call_return0, \ + .type = 1, \ + }; \ + ARCH_DEFINE_STATIC_CALL_RET0_TRAMP(name) + #define static_call_cond(name) (void)__static_call(name) #define EXPORT_STATIC_CALL(name) \ EXPORT_SYMBOL(STATIC_CALL_KEY(name)); \ EXPORT_SYMBOL(STATIC_CALL_TRAMP(name)) - #define EXPORT_STATIC_CALL_GPL(name) \ EXPORT_SYMBOL_GPL(STATIC_CALL_KEY(name)); \ EXPORT_SYMBOL_GPL(STATIC_CALL_TRAMP(name)) +/* Leave the key unexported, so modules can't change static call targets: */ +#define EXPORT_STATIC_CALL_TRAMP(name) \ + EXPORT_SYMBOL(STATIC_CALL_TRAMP(name)); \ + ARCH_ADD_TRAMP_KEY(name) +#define EXPORT_STATIC_CALL_TRAMP_GPL(name) \ + EXPORT_SYMBOL_GPL(STATIC_CALL_TRAMP(name)); \ + ARCH_ADD_TRAMP_KEY(name) + #elif defined(CONFIG_HAVE_STATIC_CALL) -static inline int static_call_init(void) { return 0; } +#define static_call_initialized 0 -struct static_call_key { - void *func; -}; +static inline int static_call_init(void) { return 0; } #define DEFINE_STATIC_CALL(name, _func) \ DECLARE_STATIC_CALL(name, _func); \ @@ -207,7 +245,13 @@ struct static_call_key { }; \ ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name) -#define static_call(name) __static_call(name) +#define DEFINE_STATIC_CALL_RET0(name, _func) \ + DECLARE_STATIC_CALL(name, _func); \ + struct static_call_key STATIC_CALL_KEY(name) = { \ + .func = __static_call_return0, \ + }; \ + ARCH_DEFINE_STATIC_CALL_RET0_TRAMP(name) + #define static_call_cond(name) (void)__static_call(name) static inline @@ -224,36 +268,46 @@ static inline int static_call_text_reserved(void *start, void *end) return 0; } +extern long __static_call_return0(void); + #define EXPORT_STATIC_CALL(name) \ EXPORT_SYMBOL(STATIC_CALL_KEY(name)); \ EXPORT_SYMBOL(STATIC_CALL_TRAMP(name)) - #define EXPORT_STATIC_CALL_GPL(name) \ EXPORT_SYMBOL_GPL(STATIC_CALL_KEY(name)); \ EXPORT_SYMBOL_GPL(STATIC_CALL_TRAMP(name)) +/* Leave the key unexported, so modules can't change static call targets: */ +#define EXPORT_STATIC_CALL_TRAMP(name) \ + EXPORT_SYMBOL(STATIC_CALL_TRAMP(name)) +#define EXPORT_STATIC_CALL_TRAMP_GPL(name) \ + EXPORT_SYMBOL_GPL(STATIC_CALL_TRAMP(name)) + #else /* Generic implementation */ +#define static_call_initialized 0 + static inline int static_call_init(void) { return 0; } -struct static_call_key { - void *func; -}; +static inline long __static_call_return0(void) +{ + return 0; +} -#define DEFINE_STATIC_CALL(name, _func) \ +#define __DEFINE_STATIC_CALL(name, _func, _func_init) \ DECLARE_STATIC_CALL(name, _func); \ struct static_call_key STATIC_CALL_KEY(name) = { \ - .func = _func, \ + .func = _func_init, \ } +#define DEFINE_STATIC_CALL(name, _func) \ + __DEFINE_STATIC_CALL(name, _func, _func) + #define DEFINE_STATIC_CALL_NULL(name, _func) \ - DECLARE_STATIC_CALL(name, _func); \ - struct static_call_key STATIC_CALL_KEY(name) = { \ - .func = NULL, \ - } + __DEFINE_STATIC_CALL(name, _func, NULL) -#define static_call(name) \ - ((typeof(STATIC_CALL_TRAMP(name))*)(STATIC_CALL_KEY(name).func)) +#define DEFINE_STATIC_CALL_RET0(name, _func) \ + __DEFINE_STATIC_CALL(name, _func, __static_call_return0) static inline void __static_call_nop(void) { } |