Re: Avoiding unnecessary jump relocations in gas?

[Andy Lutomirski]

On Mon, May 18, 2015 at 1:34 PM, H. Peter Anvin <hpa@xxxxxxxxx> 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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