On Fri, May 08, 2020 at 12:38:30PM +0200, Peter Zijlstra wrote: > Subject: objtool: Allow no-op CFI ops in alternatives > From: Peter Zijlstra <[email protected]> > Date: Fri May 8 12:34:33 CEST 2020 > > Randy reported a false-positive: "alternative modifies stack". > > What happens is that: > > alternative_io("movl %0, %P1", "xchgl %0, %P1", X86_BUG_11AP, > 13d: 89 9d 00 d0 7f ff mov %ebx,-0x803000(%rbp) > > decodes to an instruction with CFI-ops because it modifies RBP. > However, due to this being a !frame-pointer build, that should not in > fact change the CFI state. > > So instead of dis-allowing any CFI-op, verify the op would've actually > changed the CFI state. > > Fixes: 7117f16bf460 ("objtool: Fix ORC vs alternatives") > Reported-by: Randy Dunlap <[email protected]> > Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
It helps to put an example of the fixed warning in the commit log, like: This fixes the following warning: arch/x86/hyperv/hv_apic.o: warning: objtool: hv_apic_write()+0x25: alternative modifies stack Otherwise it looks good. Acked-by: Josh Poimboeuf <[email protected]> -- Josh
