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Re: [PATCH] x86: slightly simplify MB2/EFI "magic" check
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 13 Aug 2024 09:02:19 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 13 Aug 2024 07:02:29 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 12.08.2024 23:40, Andrew Cooper wrote:
> On 08/08/2024 9:49 am, Jan Beulich wrote:
>> --- a/xen/arch/x86/boot/head.S
>> +++ b/xen/arch/x86/boot/head.S
>> @@ -233,13 +233,11 @@ __efi64_mb2_start:
>>
>> /* Check for Multiboot2 bootloader. */
>> cmp $MULTIBOOT2_BOOTLOADER_MAGIC,%eax
>> - je .Lefi_multiboot2_proto
>>
>> /* Jump to .Lnot_multiboot after switching CPU to x86_32 mode. */
>> lea .Lnot_multiboot(%rip), %r15
>> - jmp x86_32_switch
>> + jne x86_32_switch
>>
>> -.Lefi_multiboot2_proto:
>> /* Zero EFI SystemTable, EFI ImageHandle addresses and cmdline. */
>> xor %esi,%esi
>> xor %edi,%edi
>
>
> You've split the logical in two, and now the comment is in the wrong
> position.
>
> If you're going to make this change, it wants to end up reading:
>
> /* Jump to .Lnot_multiboot after switching CPU to x86_32 mode. */
> lea .Lnot_multiboot(%rip), %r15
>
> /* Check for Multiboot2 bootloader. */
> cmp $MULTIBOOT2_BOOTLOADER_MAGIC,%eax
> jne x86_32_switch
>
>
> Not that it's really relevant, but this form also macrofuses nicely.
All true, yet I'm sure you also read my response to Alejandro: Then we
ought to also change the other similar instances. The goal of this simple
change, after all, is to get all similar pieces of code into consistent
shape.
Jan
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