On Fri, Apr 24, 2020 at 02:30:28PM -0500, Josh Poimboeuf wrote: > On Thu, Apr 23, 2020 at 02:47:25PM +0200, Peter Zijlstra wrote: > > .macro CALL_NOSPEC reg:req > > #ifdef CONFIG_RETPOLINE > > - ANNOTATE_NOSPEC_ALTERNATIVE > > - ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; call *%\reg),\ > > - __stringify(RETPOLINE_CALL %\reg), X86_FEATURE_RETPOLINE,\ > > - __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; call *%\reg), > > X86_FEATURE_RETPOLINE_AMD > > + /* > > + * This cannot be ALTERNATIVE_2 like with JMP_NOSPEC, because ORC > > + * unwind data is alternative invariant and needs stack modifying > > + * instructions to be in the same place for all alternatives. > > + * > > + * IOW the CALL instruction must be at the same offset for all cases. > > + */ > > + ALTERNATIVE "", "lfence", X86_FEATURE_RETPOLINE_AMD > > + ALTERNATIVE __stringify(ANNOTATE_RETPOLINE_SAFE; call *%\reg), \ > > + __stringify(call __x86_retpoline_\reg), > > X86_FEATURE_RETPOLINE > > I'm missing why ALTERNATIVE_2 wouldn't work here. How is the call a > "stack modifying instruction"? It's not an intra-function call so it > shouldn't affect ORC at all, right?
My bad. I find it hard not to consider CALL a stack modification. Let me fix that.
