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Re: [PATCH] x86: Stop relying on magic jmp behavior for early_idt_handlers
- From: "H. Peter Anvin" <hpa at zytor dot com>
- To: Andy Lutomirski <luto at amacapital dot net>
- Cc: Andy Lutomirski <luto at kernel dot org>, X86 ML <x86 at kernel dot org>, "H.J. Lu" <hjl dot tools at gmail dot com>, Borislav Petkov <bp at alien8 dot de>, Jan Beulich <JBeulich at suse dot com>, Binutils <binutils at sourceware dot org>, "linux-kernel at vger dot kernel dot org" <linux-kernel at vger dot kernel dot org>
- Date: Thu, 21 May 2015 17:50:03 -0700
- Subject: Re: [PATCH] x86: Stop relying on magic jmp behavior for early_idt_handlers
- Authentication-results: sourceware.org; auth=none
- References: <5bf75d3abce25ec615048075705f120b331aaf0b dot 1432253793 dot git dot luto at kernel dot org> <555E791D dot 1000700 at zytor dot com> <CALCETrVTqTA+Xem3dUkWo46zmk5taG0U=2BmDJLj-S80QNjP7g at mail dot gmail dot com>
On 05/21/2015 05:38 PM, Andy Lutomirski wrote:
> On Thu, May 21, 2015 at 5:32 PM, H. Peter Anvin <hpa@zytor.com> wrote:
>> On 05/21/2015 05:17 PM, Andy Lutomirski wrote:
>>>
>>> diff --git a/arch/x86/include/asm/segment.h b/arch/x86/include/asm/segment.h
>>> index 5a9856eb12ba..4bbe0eb24d7e 100644
>>> --- a/arch/x86/include/asm/segment.h
>>> +++ b/arch/x86/include/asm/segment.h
>>> @@ -231,12 +231,21 @@
>>> #define TLS_SIZE (GDT_ENTRY_TLS_ENTRIES* 8)
>>>
>>> #ifdef __KERNEL__
>>> -#ifndef __ASSEMBLY__
>>>
>>> -extern const char early_idt_handlers[NUM_EXCEPTION_VECTORS][2+2+5];
>>> +/*
>>> + * 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
>>> +#ifndef __ASSEMBLY__
>>> +extern const char early_idt_handlers[NUM_EXCEPTION_VECTORS][EARLY_IDT_HANDLER_STRIDE];
>>> #ifdef CONFIG_TRACING
>>> # define trace_early_idt_handlers early_idt_handlers
>>> #endif
>>> +#endif
>>> +
>>> +#ifndef __ASSEMBLY__
>>>
>>
>> Please get rid of the unnecessary #ifndef/#endif pair.
>
> I did it to preserve logical nesting. I didn't want the pile of
> early_idt_handlers declarations and comments to have the side affect
> of starting an #ifdef block.
>
> If you still think I should change it, I'll change it.
>
Please change it. We generally don't do that kind of logical nesting,
it is just clutter.
-hpa