Aarch64 port for ZGC, so far

[Stuart Monteith]

Thanks for pointing that out Ma Chunhui,

What you suggest can't be done as ZGC isn't just a compile time
option, it is also a run-time option. You are quite right though - the
array prologue needs to take the src and dest and decide what it needs
to do.

I'll incorporate this into the aarch64 specific code by adding the
source too the method signature and the other dependencies in a manner
that will be correct for with/without ZGC.

This will explain some of the rarer problems I 'm seeing.

On Thu, 29 Nov 2018 at 06:13, machunhui (C) <machunhui2 at huawei.com> wrote:
>
> Hi, Stuart
>
>   With your latest patch, It seems that Interpreter and C1 works fine on my machine and my case. But there is a crash when using C2.
>
>
>
> My Option is:  -XX:+UseZGC -XX:-TieredCompilation -XX:ParallelGCThreads=1 -XX:ConcGCThreads=1 -XX:+Use64BitLiteralOops
>
> And the crash happens only when java main thread is exited, after DestroyJavaVM.
>
>
>
> The crash stack:
>
> 30 V  [libjvm.so+0x121b968]  ZPage::is_active() const+0xc
>
>   31 V  [libjvm.so+0x123b180]  ZMark::try_mark_object(ZMarkCache*, unsigned long, bool)+0x48
>
>   32 V  [libjvm.so+0x123b28c]  ZMark::mark_and_follow(ZMarkCache*, ZMarkStackEntry)+0x6c
>
>   33 V  [libjvm.so+0x123e6d4]  bool ZMark::drain<ZMarkNoTimeout>(ZMarkStripe*, ZMarkThreadLocalStacks*, ZMarkCache*, ZMarkNoTimeout*)+0x7c
>
>
>
> The crash is because when trying to mark object, it failed to find page for the given object address, which is 0xbaadbabe. And the reason is because in StubGenerator:: generate_disjoint_copy, when trying to add load-barrier in aarch64, the barrier is wrongly added to dest, not src.
>
> So the fix is quite simple, when using ZGC, add load-barrier to src instead of dest.
>
>
>
> diff --git a/src/hotspot/cpu/aarch64/stubGenerator_aarch64.cpp b/src/hotspot/cpu/aarch64/stubGenerator_aarch64.cpp
>
> index a1fd069c7b..fc7f209d62 100644
>
> --- a/src/hotspot/cpu/aarch64/stubGenerator_aarch64.cpp
>
> +++ b/src/hotspot/cpu/aarch64/stubGenerator_aarch64.cpp
>
> @@ -1377,7 +1377,11 @@ class StubGenerator: public StubCodeGenerator {
>
>      }
>
>
>
>      BarrierSetAssembler *bs = BarrierSet::barrier_set()->barrier_set_assembler();
>
> +#if INCLUDE_ZGC
>
> +    bs->arraycopy_prologue(_masm, decorators, is_oop, s, count, saved_reg);
>
> +#else
>
>      bs->arraycopy_prologue(_masm, decorators, is_oop, d, count, saved_reg);
>
> +#endif
>
>
>
>      if (is_oop) {
>
>        // save regs before copy_memory
>
> @@ -1451,7 +1455,11 @@ class StubGenerator: public StubCodeGenerator {
>
>      }
>
>
>
>      BarrierSetAssembler *bs = BarrierSet::barrier_set()->barrier_set_assembler();
>
> +#if INCLUDE_ZGC
>
> +    bs->arraycopy_prologue(_masm, decorators, is_oop, s, count, saved_regs);
>
> +#else
>
>     bs->arraycopy_prologue(_masm, decorators, is_oop, d, count, saved_regs);
>
> +#endif
>
>
>
>      if (is_oop) {
>
>        // save regs before copy_memory
>
>
>
> Thanks.
>
>
>
> --------------------------------------------------
> 马春辉 Ma Chunhui
> Mail: machunhui2 at huawei.com
> 2012实验室-语言虚拟机实验室
> 2012 Laboratories-Language VM Lab,2012Labs
>
>