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Subject: Re: [PATCH] x86/acrn: Improve ACRN hypercalls
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To:     Uros Bizjak <ubizjak@gmail.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>
References: <20220804180358.32944-1-ubizjak@gmail.com>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <20220804180358.32944-1-ubizjak@gmail.com>
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On 8/4/22 11:03, Uros Bizjak wrote:
> As explained in section 6.47.5.2, "Specifying Registers for Local Variables"
> of the GCC info documentation, the correct way to specify register for
> input operands when calling Extended 'asm' is to define a local register
> variable and associate it with a specified register:
> 
> 	register unsigned long r8 asm ("r8") = hcall_id;

IIRC, that's what the ACRN folks proposed first.  But, it's more fragile
because you can't, for instance, put a printk() in that function between
the variable definition and assebly.