static_call/x86: Add __static_call_return0()
mainline inclusion from mainline-5.12-rc1 commit 3f2a8fc4 category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I410UT CVE: NA Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3f2a8fc4b15de18644e8a80a09edda168676e22c --------------------------- 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: NPeter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: NFrederic Weisbecker <frederic@kernel.org> Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: NIngo Molnar <mingo@kernel.org> Link: https://lkml.kernel.org/r/20210118141223.123667-2-frederic@kernel.orgSigned-off-by: NMa Junhai <majunhai2@huawei.com> Reviewed-by: NChen Hui <judy.chenhui@huawei.com> Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
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