On Fri, 16 Jul 2021 10:24:56 GMT, Nick Gasson <ngas...@openjdk.org> wrote:
> The clhsdb jstack command crashes when the debugged program is run with
> `-Xcomp -XX:+StressGCM -XX:StressSeed=2` on AArch64:
>
>
> sun.jvm.hotspot.utilities.AssertionFailure: sanity check
> at jdk.hotspot.agent/sun.jvm.hotspot.utilities.Assert.that(Assert.java:32)
> at
> jdk.hotspot.agent/sun.jvm.hotspot.runtime.RegisterMap.setLocation(RegisterMap.java:160)
> at
> jdk.hotspot.agent/sun.jvm.hotspot.compiler.ImmutableOopMapSet.updateRegisterMap(ImmutableOopMapSet.java:303)
> at
> jdk.hotspot.agent/sun.jvm.hotspot.runtime.aarch64.AARCH64Frame.senderForCompiledFrame(AARCH64Frame.java:407)
>
>
> The assertion failure here is:
>
>
> Assert.that(0 <= i && i < regCount, "sanity check");
>
>
> I.e. there's an invalid register in the oop map.
>
> The problem seems to be caused by the changes in JDK-8231586 which changed
> `OopMapValue::oop_types` from a bit mask to normal integer enum. However the
> changes in the C++ code weren't mirrored in SA's OopMapStream which still
> treats OopTypes as a bit mask.
>
> The particular oop map this is crashing on looks like this:
>
>
> ImmutableOopMap {[24]=Oop [32]=Oop [40]=Derived_oop_[24] } pc offsets: 324
>
>
> The code is looking for callee saved values (type=2) by AND-ing with each oop
> value type in the set, so it wrongly interprets the derived oop [40] (type=3)
> as a callee saved register.
>
> This patch just mirrors the changes to the C++ code into the corresponding SA
> classes. The C++ OopMapStream constructor no longer takes a type filter
> argument and callers are expected filter themselves, so I've made the same
> change to the Java code.
>
> This bug can also be seen using the clhsdb "disassemble" command. For
> example the above oop map is currently printed incorrectly as:
>
>
> OopMap:
> NarrowOops:[40]
> Callee saved:[40] = [24]
> Derived oops:[40] = [24]
>
>
> With this patch it becomes:
>
>
> OopMap:
> Oops:[24] [32]
> Derived oops:[40] = [24]
>
>
> This bug was reported on AArch64 but it seems to be just luck that we don't
> see it on other platforms.
>
> Tested tier1 and hotspot_serviceability on AArch64 and x86.
Good.
-------------
Marked as reviewed by kvn (Reviewer).
PR: https://git.openjdk.java.net/jdk/pull/4807
