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SubjectRe: Avoiding unnecessary jump relocations in gas?
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


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