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

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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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17

arch/x86/kernel/static_call.c

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12

include/linux/static_call.h

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5

kernel/static_call.c

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