ORC JIT Weekly #44 -- MachO debugging support enabled

Hi All,

OrcRTBridge cleanup has been set aside briefly. Instead of working on that I’m going to take a shot at getting MachO debugging support working in time for the dev meeting.

Success! MachO debugging support has landed in [1] (with an obligatory round of revert/reapply for bot failures). This support ended up being easier to implement than I had hoped, largely thanks to all the infrastructure put in place by Stefan Granitz’s earlier work on ELF debugging, as well as some help from Fred Riss and Jim Ingham. Thanks everyone!

The new support has been enabled in the llvm-jitlink tool (we should be able to add it to lli soon too). If you want to test it out on Darwin you can run:

% clang -O0 -g -c -o my-program.o my-program.c

% lldb llvm-jitlink
(lldb) settings set plugin.jit-loader.gdb.enable on
(lldb) b
(lldb) run my-program.o

If you set a breakpoint on main beware that you’ll hit it twice: First llvm-jitlink’s own main, and then then my-program.o’s. Either way, once you hit your breakpoint you should then be able to step through JIT’d code.

This is brand new, so please let me know if you run into any issues with it. Bug reports are very welcome.

Enabling the support in your own JIT should be relatively straightforward. You just need to include llvm/ExecutionEngine/Orc/DebuggerSupportPlugin.h, then install the GDBJITDebugInfoRegistrationPlugin in your object linking layer. You can see llvm-jitlink’s code for this at [2]:

GDBJITDebugInfoRegistrationPlugin::Create(this->ES, *MainJD, TT)));

In the future we’ll try to merge the ELF DebugObjectManagerPlugin and the new GDBJITDebugInfoRegistrationPlugin so that you only have to enable the one plugin regardless of platform.

– Lang.

[1] https://github.com/llvm/llvm-project/commit/e1933a0488a50eb939210808fc895d374570d891
[2] https://github.com/llvm/llvm-project/blob/0d1d058544446b5fc74e70827a021a017facc56a/llvm/tools/llvm-jitlink/llvm-jitlink.cpp#L1000