[aarch64-port-dev ] Very large code caches

Leslie Zhai lesliezhai at llvm.org.cn
Wed May 16 07:41:16 UTC 2018

Hi Andrew,

Thanks for your quick response!

在 2018年05月16日 15:35, Andrew Haley 写道:
> Hi,
> On 05/16/2018 08:27 AM, Leslie Zhai wrote:
>>> 在 2018年05月16日 15:23, Andrew Haley 写道:
>>> On 05/16/2018 03:53 AM, Leslie Zhai wrote:
>>>> Hi HotSpot developers,
>>>> I am trying to implement `patch_verified_entry` for other targets, such
>>>> as riscv, but I found that:
>>>>> but the real problem is that the resulting call
>>>>> site is not MT-safe: it can't be patched atomically.  To make that
>>>>> work we'd have to move the destination address into the constant pool.
>>> Where is that comment?  I can't find it.
>> http://mail.openjdk.java.net/pipermail/aarch64-port-dev/2014-January/000642.html
> I changed my mind after that, and we implemented trampolines.
I will learn it, thanks for your teaching!

>>>> So aarch64 hasn't implemented patched *atomically* yet?
>>> We atomically patch everything correctly.  If you look at the AArch64
>>> implementation of patch_verified_entry you'll see that we replace a
>>> direct call instruction if it can reach, and if it can't we jump to a
>>> trampoline.  The trampoline is a load from a single word followed by
>>> an indirect call.  In both cases it is atomic.
>> Cool!
>> And could you share your experience to use PRINT_REG alike or something
>> else to catch the bugs for logical issue?
> I don't really understand that message.  There are problems with the lines
> being broken, and the output is combined with PrintCompilation messages.
> I don't think I've used PRINT_REG.  If I've had problems with code
> generation I've usually stepped through in the debugger.
hhh, it often costs me several days to debug a stupid bug to find the 
*WHERE*, but only several seconds to modify the code :P

Leslie Zhai

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