lkml.org 
[lkml]   [2015]   [May]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Avoiding unnecessary jump relocations in gas?
On 05/20/2015 01:53 PM, Andy Lutomirski wrote:
> 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.

Actually it does... we align to the beginning of each slot. If .balign
could be something other than a power of 2 that would work, too.

I was mostly looking to minimize the amount of gas magic we rely on.

> 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.

If that works too with all the versions of gas we care about, that would
be fine (and I do appreciate the explicitness.) However, .[b]align is
something that will have been well exercised in every version of gas, so
I do feel slightly safer with it.

-hpa



\
 
 \ /
  Last update: 2015-05-20 23:21    [W:0.079 / U:0.844 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site