Re: [PATCH v3 16/16] objtool,x86: Rewrite retpoline thunk calls

[Nathan Chancellor]

On 6/8/2021 11:17 AM, Peter Zijlstra wrote:
> On Tue, Jun 08, 2021 at 10:29:56AM -0700, Nathan Chancellor wrote:
> > Unfortunately, this is the VM provided by the Windows Subsystem for Linux so
> > examining it is nigh-impossible :/ I am considering bisecting the transforms
> > that objtool does to try and figure out the one that causes the machine to
> > fail to boot or try to reproduce in a different hypervisor, unless you have
> > any other ideas.
>
> Does breaking Windows earn points similar to breaking the binary
> drivers? :-) :-)

:)

> The below should kill this latest transform and would quickly confirm if
> the that is causing your problem. If that's not it, what was your last
> known working version?

Yes, that diff gets me back to booting. I will see if I can figure out 
the exact rewrite that blows everything up.

> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> index e5947fbb9e7a..d0f231b9c5a1 100644
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -1857,10 +1857,10 @@ static int decode_sections(struct objtool_file *file)
>   	 * Must be after add_special_section_alts(), since this will emit
>   	 * alternatives. Must be after add_{jump,call}_destination(), since
>   	 * those create the call insn lists.
> -	 */
>   	ret = arch_rewrite_retpolines(file);
>   	if (ret)
>   		return ret;
> +	 */
>   
>   	return 0;
>   }

Cheers,
Nathan