Messages in this thread | | | Date | Wed, 28 Aug 2019 11:34:33 -0500 | From | Josh Poimboeuf <> | Subject | Re: linux-next: Tree for Aug 27 (objtool) |
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On Wed, Aug 28, 2019 at 11:13:31AM -0500, Josh Poimboeuf wrote: > Turns out this patch does break something: > > arch/x86/xen/enlighten_pv.o: warning: objtool: xen_cpuid()+0x25: can't find jump dest instruction at .text+0x9c > > I'll need to figure out a better way to whitelist that > XEN_EMULATE_PREFIX fake instruction thing. I'll probably just teach > the objtool decoder about it.
Hi Masami,
Is it possible for the kernel x86 decoder to recognize the XEN_EMULATE_PREFIX prefix?
asm(XEN_EMULATE_PREFIX "cpuid" : "=a" (*ax), "=b" (*bx), "=c" (*cx), "=d" (*dx) : "0" (*ax), "2" (*cx));
is disassembled to:
33: 0f 0b ud2 35: 78 65 js 9c <xen_store_tr+0xc> 37: 6e outsb %ds:(%rsi),(%dx) 38: 0f a2 cpuid
which confuses objtool. Presumably that would confuse other users of the decoder as well.
That's a highly unlikely sequence of instructions, maybe the kernel decoder should recognize it as a single instruction.
-- Josh
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