linux-kernel - Re: [PATCH v1 0/3] x86/boot: Supply boot_param in rdi instead of rsi from startup

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Message-ID: <DE5A95F1-CACB-4CF5-B459-3DFEC294DDD9@zytor.com>
Date: Mon, 23 Jun 2025 17:49:22 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Khalid Ali <khaliidcaliy@...il.com>, brgerst@...il.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        ubizjak@...il.com
CC: x86@...nel.org, linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 0/3] x86/boot: Supply boot_param in rdi instead of rsi from startup_64()

On June 23, 2025 11:39:09 AM PDT, Khalid Ali <khaliidcaliy@...il.com> wrote:
>> This is also invoked by some external bootloaders that boot the ELF 
>> image directly, even though this is strongly discouraged.
>>
>> Therefore this patchset is NAKed with extreme prejudice.
>
>Thanks both of you peter and brian,
>
>however, the boot protocol document saying "%rsi must hold the base address of the struct boot_params",
>it doesn't mention why. Maybe the document needs update to justify the reasons. I wouldn't have known it 
>if you didn't tell me, so this shouldn't confuse anyone else.
>
>Thanks 
>Khalid Ali

It is a *protocol*. An interface. "Because the interface specification says so" is really all the justification you need; otherwise you have to hunt down *every* user of the interface and verify your change.