Zeke Medley (May 31 2021 at 19:30): Zeke Medley (May 31 2021 at 19:30):Hi there - I'm currently a little stuck working out how to generate / work with unwind information and the cranelift JIT. From this blog post by Nick Fitzgerald it seems like doing so is possible, when I call this function from Cranelift code though I don't see Cranelift frames in the backtrace. Is there documentation somewhere about how this is supposed to work or an example of getting unwind information working?
bjorn3 (May 31 2021 at 20:52):You need to create and register an unwind table with the stack unwinder.
bjorn3 (May 31 2021 at 20:54):https://github.com/bjorn3/rustc_codegen_cranelift/blob/40dd3e2b7089b5e96714e064b731f6dbf17c61a9/src/debuginfo/unwind.rs is a bare bone example. It also handles aot compilation, but never unregisters the unwind table.
bjorn3 (May 31 2021 at 20:56):https://github.com/bytecodealliance/wasmtime/blob/40d546c420c1e6c4909fc80e048dd1854fda1cd6/crates/jit/src/unwind/systemv.rs is the wasmtime implementation which does support unregistering.
bjorn3 (May 31 2021 at 20:56):@Zeke Medley
Zeke Medley (Jun 12 2021 at 19:03):Thanks a bunch for the info @bjorn3 . After moving your example code over from rustc_codegen_cranelift into my JIT and calling add_function/register_jit after function definition and jit.finalize_definitions respectively I'm still not seeing Cranelift stack frames in my backtrace. Is there anything specific about how I call Backtrace::new or configure the JIT that I should to be doing here?
Zeke Medley (Jun 12 2021 at 19:04):More generally here my goal is to be able to walk the call stack at runtime to find live roots for garbage collection. If there is a better way to do that I'd also be open to a different approach.
bjorn3 (Jun 12 2021 at 19:23):After __register_frame stack unwinding will work.
bjorn3 (Jun 12 2021 at 19:24):You will separately need to store the stackmap to use during root tracing.
Zeke Medley (Jun 12 2021 at 21:18):Interesting - I must be doing something wrong then :) do you know if there is somewhere I can find documentation on how __register_frame works? Googling around didn't yield much
Zeke Medley (Jun 12 2021 at 23:25):Phew - my issue was that I wasn't registering builtin function. Working as expected now. Thanks so much for the help @bjorn3 !
bjorn3 (Jun 13 2021 at 05:57):glad it works now
Last updated: Dec 23 2024 at 12:05 UTC