Re: [Xen-devel] [PATCH 03/18] x86/boot: use %ecx instead of %eax

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 30.01.15 at 18:54, <daniel.kiper@xxxxxxxxxx> wrote:
>          /* Save the Multiboot info struct (after relocation) for later use. 
> */
>          mov     $sym_phys(cpu0_stack)+1024,%esp
> -        push    %ebx
> -        call    reloc
> +        mov     %ecx,%eax
> +        push    %ebx                /* Multiboot information address */
> +        call    reloc               /* %eax contains trampoline address */

This last part looks completely unrelated to the change made here
(and contrary to the description, as here you clobber %eax while
the description says reloc() needs it unclobbered); afaict it belongs
in whatever patch add the consumption of this value in reloc().
That said - passing parameters to reloc() by two different means
looks very odd too. I'm clearly of the opinion that parameter
passing should follow an existing convention unless entirely
unfeasible. Which then raises the question whether this patch is
really needed: Rather than fiddling with a lot of code, can't you
just copy the incoming %eax into some other register, making this
a single line change that can again simply be done in the patch
where you actually consume the new information?

Jan


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