Re: [PATCHv11 05/19] x86/relocate_kernel: Use named labels for less confusion

["H. Peter Anvin" <hpa@xxxxxxxxx>]

On 5/29/24 03:47, Nikolay Borisov wrote:
> > diff --git a/arch/x86/kernel/relocate_kernel_64.S 
> > b/arch/x86/kernel/relocate_kernel_64.S
> > index 56cab1bb25f5..085eef5c3904 100644
> > --- a/arch/x86/kernel/relocate_kernel_64.S
> > +++ b/arch/x86/kernel/relocate_kernel_64.S
> > @@ -148,9 +148,10 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
> >        */
> >       movl    $X86_CR4_PAE, %eax
> >       testq    $X86_CR4_LA57, %r13
> > -    jz    1f
> > +    jz    .Lno_la57
> >       orl    $X86_CR4_LA57, %eax
> > -1:
> > +.Lno_la57:
> > +
> >       movq    %rax, %cr4
> >       jmp 1f
>
> That jmp 1f becomes redundant now as it simply jumps 1 line below.

Uh... am I the only person to notice that ALL that is needed here is:

	andl $(X86_CR4_PAE|X86_CR4_LA57), %r13d
	movq %r13, %rax

... since %r13 is dead afterwards, and PAE *will* have been set in %r13 
already?

I don't believe that this specific jmp is actually needed -- there are 
several more synchronizing jumps later -- but it doesn't hurt.

However, if the effort is for improving the readability, it might be 
worthwhile to encapsulate the "jmp 1f; 1:" as a macro, e.g. "SYNC_CODE".

	-hpa