Re: [tip: objtool/core] jump_label, x86: Allow short NOPs

[Josh Poimboeuf]

On Tue, May 18, 2021 at 10:24:43PM +0200, Peter Zijlstra wrote:
> OK, willy followed up on IRC, and it turns out there's a kbuild
> dependency missing; then objtool changes we don't rebuild:
> 
>   arch/x86/entry/vdso/vma.o
> 
> even though we should, this led to an unpatched 2 byte jump-label and
> things went sideways. I'm not sure I understand the whole build
> machinery well enough to know where to begin chasing this.
> 
> Now, this file is mighty magical, due to:
> 
> arch/x86/entry/vdso/Makefile:OBJECT_FILES_NON_STANDARD  := y
> arch/x86/entry/vdso/Makefile:OBJECT_FILES_NON_STANDARD_vma.o    := n
> 
> Maybe that's related.

I'm not exactly thrilled that objtool now has the power to easily brick
a system :-/  Is it really worth it?

Anyway, here's one way to fix it.  Maybe Masahiro has a better idea.