[LLVMdev] [AArch64] Question about far call

[weimingz at codeaurora.org]

Hi Tim,

Thanks for answering.
I also tried armlink 6 for aarch64. It inserts veneer too. So gnu ld is
not doing the job very well.
My current workaround is declaring those functions as function pointers
and compile with -mcmodel=large to force compiler to generate 4 movs and
"blr".

Thanks,
Weiming

> Hi Weiming,
>
> On 20 June 2014 02:01, Weiming Zhao <weimingz at codeaurora.org> wrote:
>> PS. The above test works fine with arm v7 targart. (clang emits “bl
>> foo” and
>> ld generates veneer)
>
> This is what I'd expect ld to do in the AArch64 case too. Most of the
> time the destination (or its stub) is in range, so general codegen
> shouldn't be penalised by having to emit movz/movk sequences &
> indirect branches for each call.
>
> Unfortunately, the AArch64 (& ARM) ELF ABI appears to make it a QoI
> issue by using vague wording in section 4.6.7 ("a linker *may* use a
> veneer..."). I'm still surprised they haven't done that yet though; I
> wonder if there's a bug lying around.
>
> Cheers.
>
> Tim.
>