Re: [Xen-devel] [PATCH v3 1/5] x86/boot: Only jump into low trampoline code for real-mode boot

[Jan Beulich <jbeulich@xxxxxxxx>]

On 21.08.2019 18:35, David Woodhouse wrote:
> --- a/xen/arch/x86/boot/head.S
> +++ b/xen/arch/x86/boot/head.S
> @@ -727,7 +727,17 @@ trampoline_setup:
>          /* Switch to low-memory stack which lives at the end of trampoline 
> region. */
>          mov     sym_fs(trampoline_phys),%edi
>          lea     TRAMPOLINE_SPACE+TRAMPOLINE_STACK_SPACE(%edi),%esp
> +        cmpb    $0, sym_fs(skip_realmode)
> +        jz      1f
> +        /* If no-real-mode, jump straight to trampoline_protmode_entry */
> +        lea     trampoline_protmode_entry-trampoline_start(%edi),%eax
> +        /* EBX == 0 indicates we are the BP (Boot Processor). */
> +        xor     %ebx,%ebx
> +        jmp     2f
> +1:
> +        /* Go via 16-bit code in trampoline_boot_cpu_entry */
>          lea     trampoline_boot_cpu_entry-trampoline_start(%edi),%eax
> +2:
>          pushl   $BOOT_CS32
>          push    %eax

Provided it goes in together with the subsequent change removing this
double jump again
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>

Of course it would have been nice if within you addition you'd been
consistent with adding (or not) blanks after commas separating insn
operands.

Jan

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