diff options
| -rw-r--r-- | arch/Kconfig | 3 | ||||
| -rw-r--r-- | include/linux/static_call.h | 156 | ||||
| -rw-r--r-- | include/linux/static_call_types.h | 15 |
3 files changed, 174 insertions, 0 deletions
diff --git a/arch/Kconfig b/arch/Kconfig index af14a567b493..806e6df7b47c 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -975,6 +975,9 @@ config HAVE_SPARSE_SYSCALL_NR config ARCH_HAS_VDSO_DATA bool +config HAVE_STATIC_CALL + bool + source "kernel/gcov/Kconfig" source "scripts/gcc-plugins/Kconfig" diff --git a/include/linux/static_call.h b/include/linux/static_call.h new file mode 100644 index 000000000000..d8892dff2e91 --- /dev/null +++ b/include/linux/static_call.h @@ -0,0 +1,156 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _LINUX_STATIC_CALL_H +#define _LINUX_STATIC_CALL_H + +/* + * Static call support + * + * Static calls use code patching to hard-code function pointers into direct + * branch instructions. They give the flexibility of function pointers, but + * with improved performance. This is especially important for cases where + * retpolines would otherwise be used, as retpolines can significantly impact + * performance. + * + * + * API overview: + * + * DECLARE_STATIC_CALL(name, func); + * DEFINE_STATIC_CALL(name, func); + * static_call(name)(args...); + * static_call_update(name, func); + * + * Usage example: + * + * # Start with the following functions (with identical prototypes): + * int func_a(int arg1, int arg2); + * int func_b(int arg1, int arg2); + * + * # Define a 'my_name' reference, associated with func_a() by default + * DEFINE_STATIC_CALL(my_name, func_a); + * + * # Call func_a() + * static_call(my_name)(arg1, arg2); + * + * # Update 'my_name' to point to func_b() + * static_call_update(my_name, &func_b); + * + * # Call func_b() + * static_call(my_name)(arg1, arg2); + * + * + * Implementation details: + * + * This requires some arch-specific code (CONFIG_HAVE_STATIC_CALL). + * Otherwise basic indirect calls are used (with function pointers). + * + * Each static_call() site calls into a trampoline associated with the name. + * The trampoline has a direct branch to the default function. Updates to a + * name will modify the trampoline's branch destination. + * + * If the arch has CONFIG_HAVE_STATIC_CALL_INLINE, then the call sites + * themselves will be patched at runtime to call the functions directly, + * rather than calling through the trampoline. This requires objtool or a + * compiler plugin to detect all the static_call() sites and annotate them + * in the .static_call_sites section. + */ + +#include <linux/types.h> +#include <linux/cpu.h> +#include <linux/static_call_types.h> + +#ifdef CONFIG_HAVE_STATIC_CALL +#include <asm/static_call.h> + +/* + * Either @site or @tramp can be NULL. + */ +extern void arch_static_call_transform(void *site, void *tramp, void *func); + +#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))); \ + __static_call_update(&STATIC_CALL_KEY(name), \ + STATIC_CALL_TRAMP_ADDR(name), func); \ +}) + +#if defined(CONFIG_HAVE_STATIC_CALL) + +struct static_call_key { + void *func; +}; + +#define DEFINE_STATIC_CALL(name, _func) \ + DECLARE_STATIC_CALL(name, _func); \ + struct static_call_key STATIC_CALL_KEY(name) = { \ + .func = _func, \ + }; \ + ARCH_DEFINE_STATIC_CALL_TRAMP(name, _func) + +#define static_call(name) __static_call(name) + +static inline +void __static_call_update(struct static_call_key *key, void *tramp, void *func) +{ + cpus_read_lock(); + WRITE_ONCE(key->func, func); + arch_static_call_transform(NULL, tramp, func); + cpus_read_unlock(); +} + +#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)) + +#else /* Generic implementation */ + +struct static_call_key { + void *func; +}; + +#define DEFINE_STATIC_CALL(name, _func) \ + DECLARE_STATIC_CALL(name, _func); \ + struct static_call_key STATIC_CALL_KEY(name) = { \ + .func = _func, \ + } + +#define static_call(name) \ + ((typeof(STATIC_CALL_TRAMP(name))*)(STATIC_CALL_KEY(name).func)) + +static inline +void __static_call_update(struct static_call_key *key, void *tramp, void *func) +{ + WRITE_ONCE(key->func, func); +} + +#define EXPORT_STATIC_CALL(name) EXPORT_SYMBOL(STATIC_CALL_KEY(name)) +#define EXPORT_STATIC_CALL_GPL(name) EXPORT_SYMBOL_GPL(STATIC_CALL_KEY(name)) + +#endif /* CONFIG_HAVE_STATIC_CALL */ + +#endif /* _LINUX_STATIC_CALL_H */ diff --git a/include/linux/static_call_types.h b/include/linux/static_call_types.h new file mode 100644 index 000000000000..5ed249dc47d3 --- /dev/null +++ b/include/linux/static_call_types.h @@ -0,0 +1,15 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _STATIC_CALL_TYPES_H +#define _STATIC_CALL_TYPES_H + +#include <linux/stringify.h> + +#define STATIC_CALL_KEY_PREFIX __SCK__ +#define STATIC_CALL_KEY(name) __PASTE(STATIC_CALL_KEY_PREFIX, name) + +#define STATIC_CALL_TRAMP_PREFIX __SCT__ +#define STATIC_CALL_TRAMP_PREFIX_STR __stringify(STATIC_CALL_TRAMP_PREFIX) +#define STATIC_CALL_TRAMP(name) __PASTE(STATIC_CALL_TRAMP_PREFIX, name) +#define STATIC_CALL_TRAMP_STR(name) __stringify(STATIC_CALL_TRAMP(name)) + +#endif /* _STATIC_CALL_TYPES_H */ |