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Re: Avoiding unnecessary jump relocations in gas?
- From: Andy Lutomirski <luto at amacapital dot net>
- To: "H. Peter Anvin" <hpa at zytor dot com>
- Cc: "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: Wed, 20 May 2015 13:53:45 -0700
- Subject: Re: Avoiding unnecessary jump relocations in gas?
- Authentication-results: sourceware.org; auth=none
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On Mon, May 18, 2015 at 1:34 PM, H. Peter Anvin <hpa@zytor.com> wrote:
> On 05/18/2015 01:28 PM, H. Peter Anvin wrote:
>>
>> OK, that is probably too recent. The simplest answer I think is just to
>> .balign 16 each vector. This is init space... some extra padding really
>> doesn't matter.
>>
>> Patch attached (still in compile test).
>>
>
> Corrected.
Egads. Now I understand what that code is. I don't like the balign,
since this has nothing to do with alignment -- we're creating an array
of functions.
Can't we make it explicit?
#define EARLY_IDT_HANDLER_STRIDE 9
...
.rept NUM_EXCEPTION_VECTORS
. = early_idt_handlers + i * EARLY_IDT_HANDLER_STRIDE
.if (EXCEPTION_ERRCODE_MASK >> i) & 1
ASM_NOP2
.else
pushl $0 # Dummy error code, to make stack frame uniform
.endif
pushl $i # 20(%esp) Vector number
jmp early_idt_handler
i = i + 1
.endr
gas will error out if we try to move . backwards, so this should be safe.
--Andy