Messages in this thread | | | Date | Wed, 20 May 2015 13:59:35 -0700 | From | "H. Peter Anvin" <> | Subject | Re: Avoiding unnecessary jump relocations in gas? |
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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
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