On Thu, 22 Feb 2024 13:28:43 GMT, Magnus Ihse Bursie <i...@openjdk.org> wrote:
>> Your comment had me go and elfdump the entire libjvm.so and compare the >> entire output... :-) Now at least I understand why there were so many >> spurious changes in the linux binary -- the old symbols were named e.g. >> `JVM_MonitorWait@@SUNWprivate_1.1` while the new one are just named >> `JVM_MonitorWait`. This caused the segment to be shorter, and this in turned >> offsetted all following position, so the change cascaded down. > > Ok, I see now that there is indeed a slight difference. The debug.cpp symbols > are present as local symbols in the .symtab, both before and after this > patch. However, before this patch they had visibility DEFAULT and now they > have visibility HIDDEN. I don't think this matters for anything except the > linker, but I should probably verify that they are still correctly usable > from gcc. > > I would appreciate it if someone could provide a step-by-step instruction on > how to verify these functions on gdb (I haven't used it for 10-15 years so I > apologize if I'm a bit rusty), or provide a pointer to where I can find such > instructions. Is this supposed to work on core dumps, live attached processes > or both? On a latest JDK build today, in Linux I can attach to a live process (not a core dump): gdb --pid PID ..and type: call universe() (I think you need to switch to a JavaThread first) and see on the JVM's output: "Executing universe" Heap garbage-first heap total reserved 30932992K, ...etc... Removing JNIEXPORT here on Linux and rebuilding: still works. readelf shows: existing build (using JNIEXPORT): 32252: 0000000000698160 249 FUNC LOCAL DEFAULT 11 universe without JNIEXPORT: 32252: 0000000000698160 249 FUNC LOCAL HIDDEN 11 universe So gdb on Linux can call a HIDDEN function, i.e. without the JNIEXPORT. It seems happy either way, not affected by visibility. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/17955#discussion_r1499294627
