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/* 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); \
})
#ifdef CONFIG_HAVE_STATIC_CALL_INLINE
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;
struct static_call_mod *mods;
};
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);
#define DEFINE_STATIC_CALL(name, _func) \
DECLARE_STATIC_CALL(name, _func); \
struct static_call_key STATIC_CALL_KEY(name) = { \
.func = _func, \
.mods = NULL, \
}; \
ARCH_DEFINE_STATIC_CALL_TRAMP(name, _func)
#define static_call(name) __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))
#elif 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();
}
static inline int static_call_text_reserved(void *start, void *end)
{
return 0;
}
#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);
}
static inline int static_call_text_reserved(void *start, void *end)
{
return 0;
}
#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 */
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