8185505: AArch64: Port AOT

[Vladimir Kozlov]

On 4/23/18 3:38 AM, Andrew Haley wrote:
> On 04/23/2018 08:14 AM, Yang Zhang wrote:
> 
>> I have tested the patches in my environment. AOT test cases in jtreg
>> are passed, and there aren't new failed cases in hotspot jtreg on no
>> matter aarch64 or x86 platform.
>> But when using jaotc to compile java.base with an option
>> "--compile-for-tiered", there is an overflow error on aarch64
>> platform. There isn't such an error on x86 platform.
> 
> Yep, I know that.  It's because there is a 30-bit limit in the range
> of a branch, and if we have a very large text section the offset to
> the PLT stub may be out of range.  There is some logic in the GNU
> linker to handle this, and I'll haver a look at how it works.
> 
> I don't want to hold up this patch for the overflow issue for two
> reasons.  Firstly, if you use such a huge AOT-compiled binary your
> performance will suffer greatly.  It makes much more sense to compile
> only what you need because otherwise your startup time will actually
> be slower than not using AOT compilation at all.  Secondly, I think it
> will require some reworking of the way that the AOT compiler works to
> fix this, and I'd rather do that in a later patch.

Yes, I agree with this.

Thanks,
Vladimir

> 
> Thank you.
>