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static_call/x86: Add __static_call_return0()

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Provide a stub function that return 0 and wire up the static call site
patching to replace the CALL with a single 5 byte instruction that
clears %RAX, the return value register.

The function can be cast to any function pointer type that has a
single %RAX return (including pointers). Also provide a version that
returns an int for convenience. We are clearing the entire %RAX register
in any case, whether the return value is 32 or 64 bits, since %RAX is
always a scratch register anyway.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20210118141223.123667-2-frederic@kernel.org
This commit is contained in:
Peter Zijlstra
2021-01-18 15:12:16 +01:00
committed by Ingo Molnar
parent 880cfed3a0
commit 3f2a8fc4b1
3 changed files with 32 additions and 2 deletions
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12
include/linux/static_call.h
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@@ -142,6 +142,8 @@ extern void __static_call_update(struct static_call_key *key, void *tramp, void
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) = { \
@@ -206,6 +208,11 @@ static inline int static_call_text_reserved(void *start, void *end)
return 0;
}
static inline long __static_call_return0(void)
{
return 0;
}
#define EXPORT_STATIC_CALL(name) \
EXPORT_SYMBOL(STATIC_CALL_KEY(name)); \
EXPORT_SYMBOL(STATIC_CALL_TRAMP(name))
@@ -222,6 +229,11 @@ struct static_call_key {
void *func;
};
static inline long __static_call_return0(void)
{
return 0;
}
#define DEFINE_STATIC_CALL(name, _func) \
DECLARE_STATIC_CALL(name, _func); \
struct static_call_key STATIC_CALL_KEY(name) = { \