MIPS atomic memory operations

Leslie Zhai zhaixiang at loongson.cn
Thu Jan 17 09:38:34 UTC 2019

在 2019/1/16 下午5:44, Robert O'Callahan 写道:
> On Wed, Jan 16, 2019 at 10:22 PM Leslie Zhai <zhaixiang at loongson.cn 
> <mailto:zhaixiang at loongson.cn>> wrote:
>     I simply read your technical report and noticed that porting RR to
>     ARM
>     failed due to ARM atomic memory operations use such as LL/SC
>     "load-linked/store-conditional" instructions, perhaps it is the same
>     issue for OpenJDK MIPS porting.  For example, emit_compare_and_swap
>     http://hg.loongnix.org/jdk8-mips64-public/hotspot/file/dca904de5de5/src/cpu/mips/vm/c1_LIRAssembler_mips.cpp#l3912
>     The same LL/SC "story"...
>     http://hg.loongnix.org/jdk8-mips64-public/hotspot/file/dca904de5de5/src/cpu/mips/vm/macroAssembler_mips.cpp#l2692
> Yes, it is very likely MIPS has the same problem.
> Maybe you could convince the hardware designers to add a feature to 
> optionally generate a synchronous trap when a SC instruction fails. 
> That would be enough to make rr work.

The hardware designers are *upstairs* on us.

>     Hi Robert,
>     Please teach me how to modify rr's design philosophy?  It is sure
>     a lot
>     of work but balanced cost/benefit for hunting the self-modifying
>     code's
>     bug when porting OpenJDK HotSpot JIT compilers to MIPS backend.
> I'm sure porting the Hotspot JIT to MIPS creates some very hard bugs, 
> but I think even if you found a way around the LL/SC problem, porting 
> rr to MIPS would be a lot of work. I guess it would take at least six 
> months. It's unlikely it would be worth it just to fix Hotspot JIT bugs.
> Rob
> -- 
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