Messages in this thread | | | Date | Wed, 11 Nov 2020 13:59:00 -0600 | From | Josh Poimboeuf <> | Subject | Re: WARNING: can't access registers at asm_common_interrupt |
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On Wed, Nov 11, 2020 at 08:42:06PM +0100, Peter Zijlstra wrote: > > Would objtool have an easier time coping if this were implemented in > > terms of a static call? > > I doubt it, the big problem is that there is no visibility into the > actual alternative text. Runtime patching fragments into static call > would have the exact same problem. > > Something that _might_ maybe work is trying to morph the immediate > fragments into an alternative. That is, instead of this: > > static inline notrace unsigned long arch_local_save_flags(void) > { > return PVOP_CALLEE0(unsigned long, irq.save_fl); > } > > Write it something like: > > static inline notrace unsigned long arch_local_save_flags(void) > { > PVOP_CALL_ARGS; > PVOP_TEST_NULL(irq.save_fl); > asm_inline volatile(ALTERNATIVE(paravirt_alt(PARAVIRT_CALL), > "PUSHF; POP _ASM_AX", > X86_FEATURE_NATIVE) > : CLBR_RET_REG, ASM_CALL_CONSTRAINT > : paravirt_type(irq.save_fl.func), > paravirt_clobber(PVOP_CALLEE_CLOBBERS) > : "memory", "cc"); > return __eax; > } > > And then we have to teach objtool how to deal with conflicting > alternatives... > > That would remove most (all, if we can figure out a form that deals with > the spinlock fragments) of paravirt_patch.c > > Hmm?
I was going to suggest something similar. Though I would try to take it further and replace paravirt_patch_default() with static calls.
Either way it doesn't make objtool's job much easier. But it would be nice to consolidate runtime patching mechanisms and get rid of .parainstructions.
-- Josh
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