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Message-ID: <555F98B4.4090201@zytor.com>
Date: Fri, 22 May 2015 21:00:00 -0000
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Andy Lutomirski <luto@amacapital.net>, Ingo Molnar <mingo@kernel.org>
CC: Andy Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>,        "H.J. Lu" <hjl.tools@gmail.com>, Borislav Petkov <bp@alien8.de>,        Jan Beulich <JBeulich@suse.com>, Binutils <binutils@sourceware.org>,        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] x86: Stop relying on magic jmp behavior for early_idt_handlers
References: <9b741597a52258e829bae247216da656d452395a.1432257964.git.luto@kernel.org> <20150522062224.GA4736@gmail.com> <CALCETrXja3FHMT9WSZQ86ozyi8KsFKmFeR_JDDrt6GtRSLa8OA@mail.gmail.com>
In-Reply-To: <CALCETrXja3FHMT9WSZQ86ozyi8KsFKmFeR_JDDrt6GtRSLa8OA@mail.gmail.com>
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On 05/21/2015 11:51 PM, Andy Lutomirski wrote:
>>>
>>>  #ifdef __KERNEL__
>>> +
>>> +/*
>>> + * early_idt_handlers is an array of entry points.  For simplicity, it's
>>> + * a real array.  We allocate nine bytes for each entry: two one-byte
>>> + * push instructions and a five-byte jump in the worst case.
>>> + */
>>> +#define EARLY_IDT_HANDLER_STRIDE 9
>>
>> So how come that two plus five equals nine? ;-)
> 
> A "one-byte push" would be pretty impressive :)
> 

Well, non-REX register pushes are just one byte.  However, these take an
immediate constant.

>>
>> Ditto for the 64-bit side.
> 
> Sounds good.  I'll do all this tomorrow and resend.
> 

Thank you!  Since I trust you, I'll send you this in advance:

Acked-by: H. Peter Anvin <hpa@linux.intel.com>