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SubjectRe: [PATCH 13/15] x86/static_call: Add inline static call implementation for x86-64
On Wed, Jun 05, 2019 at 03:08:06PM +0200, Peter Zijlstra wrote:
> --- a/arch/x86/include/asm/static_call.h
> +++ b/arch/x86/include/asm/static_call.h
> @@ -2,6 +2,20 @@
> #ifndef _ASM_STATIC_CALL_H
> #define _ASM_STATIC_CALL_H
>
> +#include <asm/asm-offsets.h>
> +
> +#ifdef CONFIG_HAVE_STATIC_CALL_INLINE
> +
> +/*
> + * This trampoline is only used during boot / module init, so it's safe to use
> + * the indirect branch without a retpoline.
> + */
> +#define __ARCH_STATIC_CALL_TRAMP_JMP(key, func) \
> + ANNOTATE_RETPOLINE_SAFE \
> + "jmpq *" __stringify(key) "+" __stringify(SC_KEY_func) "(%rip) \n"
> +
> +#else /* !CONFIG_HAVE_STATIC_CALL_INLINE */

I wonder if we can simplify this (and drop the indirect branch) by
getting rid of the above cruft, and instead just use the out-of-line
trampoline as the default for inline as well.

Then the inline case could fall back to the out-of-line implementation
(by patching the trampoline's jmp dest) before static_call_initialized
is set.

--
Josh

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