> On Jun 10, 2019, at 11:33 AM, Josh Poimboeuf <jpoim...@redhat.com> wrote: > > 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.
I must be missing some context - but what guarantees that this indirect branch would be exactly 5 bytes long? Isn’t there an assumption that this would be the case? Shouldn’t there be some handling of the padding?
