Great, thanks! I’ve already commented on the pr (https://github.com/openjdk/jdk/pull/11442).
Thanks, Richard. From: Boris Ulasevich <boris.ulasev...@bell-sw.com> Date: Thursday, 1. December 2022 at 09:00 To: Reingruber, Richard <richard.reingru...@sap.com>, Sergey Nazarkin <snazar...@azul.com> Cc: porters-dev@openjdk.org <porters-dev@openjdk.org> Subject: Re: Missing nmethod entry barriers on ARM32 Hi, As I know, the change for JDK-8291302 "ARM32: nmethod entry barriers support" is ready and going to be published in a few days. thanks, Boris On 11/30/2022 12:07 AM, Reingruber, Richard wrote: Hi Sergey, > Is this blocking you? As workaround I can prepare simple barriers > implementation enough to run SerialGC. The entry barriers are required for G1. Without you can get a corrupted java heap. Here's a reproducer: https://bugs.openjdk.org/browse/JDK-8288970?focusedCommentId=14520842&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-14520842 It should fail on ARM32. I'd like to do https://github.com/openjdk/jdk/pull/11314 which will make that type of issue more likely. SerialGC and ParallelGC are not affected. > Unfortunately we have no plan for this activity. I’m not familiar with the > problem so can’t estimate the time required to implement the functionality. A nmethod barrier is nothing too complicated. Without support for ZGC/Shenandoah it is basically a conditional runtime call with BarrierSetNMethod::nmethod_stub_entry_barrier() as target. Without ZGC/Shenandoah you can implement BarrierSetNMethod::deoptimize() as ShouldNotReachHere() because BarrierSetNMethod::nmethod_entry_barrier() always returns true (nmethod can be entered). The actual AARCH64 implementation is optimized and a little bit complex. It is sufficient to implement the NMethodPatchingType::stw_instruction_and_data_patch part without the extra C2 stub, i.e. slow_path==NULL in BarrierSetAssembler::nmethod_entry_barrier(..., slow_path, ...) I hardly know ARM but I really don't think it would be a lot of effort to implement it. Best regards, Richard. ________________________________ From: Sergey Nazarkin <snazar...@azul.com><mailto:snazar...@azul.com> Sent: Tuesday, November 29, 2022 15:29 To: Reingruber, Richard <richard.reingru...@sap.com><mailto:richard.reingru...@sap.com> Cc: porters-dev@openjdk.org<mailto:porters-dev@openjdk.org> <porters-dev@openjdk.org><mailto:porters-dev@openjdk.org>; boris.ulasev...@bell-sw.com<mailto:boris.ulasev...@bell-sw.com> <boris.ulasev...@bell-sw.com><mailto:boris.ulasev...@bell-sw.com> Subject: Re: Missing nmethod entry barriers on ARM32 Hi Richard, Unfortunately we have no plan for this activity. I’m not familiar with the problem so can’t estimate the time required to implement the functionality. Is this blocking you? As workaround I can prepare simple barriers implementation enough to run SerialGC. With best regards, Sergey > On 28 Nov 2022, at 13:03, Reingruber, Richard > <richard.reingru...@sap.com><mailto:richard.reingru...@sap.com> wrote: > > Dear ARM32 Maintainers, Boris, Sergey, [1] > > ARM32 does not implement nmethod entry barriers (see > https://bugs.openjdk.org/browse/JDK-8291302). > > This is actually a defect because nmethod entry barriers are a G1 requirement > where they are needed during concurrent marking to keep alive nmethod oop > constants as they are all weak oops[2]. > > I'd like to do a clean-up which removes redundant stackwalks from the G1 > remark pause[3]. With nmethod entry barriers they are not necessary as they > do the same keep alive for oop constants of nmethods found on stack. Without > nmethod barriers (ARM32) these stackwalks are not sufficient though as every > nmethod that is called during concurrent marking needs to do the keep alive > for SATB. > > Could you share your plans regarding the implementation of nmethod entry > barriers? How would you like me to handle ARM32 in the intended clean-up? > > Thanks, > Richard. > > [1] found you on https://wiki.openjdk.org/display/HotSpot/Ports > [2] https://bugs.openjdk.org/browse/JDK-8288970 > [3] https://github.com/openjdk/jdk/pull/11314