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Re: [PATCH] x86: Stop relying on magic jmp behavior for early_idt_handlers
- From: Andy Lutomirski <luto at amacapital dot net>
- To: "H. Peter Anvin" <hpa at zytor dot com>
- 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 17:38:02 -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>
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.
>
>> +/* Build the early_idt_handlers array */
>> __INIT
>> .globl early_idt_handlers
>
> Let's use ENTRY(early_idt_handlers) for consistency.
Will do.
--Andy
>
> Otherwise it looks good. I like the use of .fill better than moving .,
> it seems more robust to me.
>
> Conditionally-Acked-by: H. Peter Anvin <hpa@linux.intel.com>
>
--
Andy Lutomirski
AMA Capital Management, LLC