squirl (Mar 09 2023 at 05:14): squirl (Mar 09 2023 at 05:14):Hi, I've seen that wasmtime supports debugging wasm using regular debuggers but I can't seem to get it to work.
I've tried copying the rust code verbatim from this video, compiling with rustc --target=wasm32-wasi fizzbuzz.rs and running lldb -- wasmtime -g fizzbuzz.wasm, but setting a breakpoint with b fizzbuzz and running with r just runs the code as normal; no breakpoint is triggered.
squirl (Mar 09 2023 at 05:15):I've also tried with gdb, with similar results
squirl (Mar 09 2023 at 07:09):Seems like I was using an outdated version of wasmtime, working now! :)
Scott Waye (Sep 22 2023 at 20:07):Is -g still an option for wasmtime or is it now -D debug-info=y ?
Scott Waye (Sep 22 2023 at 20:08):i.e. when given a WASM file compiled from dwarf LLVM bitcode?
Alex Crichton (Sep 22 2023 at 21:14):it'd -D debug-info, which is equivalent to -D debug-info=y.
Alex Crichton (Sep 22 2023 at 21:14):I figure we can reintroduce -g if necessary though
Scott Waye (Sep 25 2023 at 12:59):A follow up if I may. Is there a way in LLDB to print class static fields from a c++ object?
I try
(lldb) p WKS::gc_heap::g_low_memory_status
error: Couldn't lookup symbols:
WKS::gc_heap::g_low_memory_status
But it can't find the symbol.
Alex Crichton (Sep 25 2023 at 14:42):I've never used lldb with wasmtime to that degree, so not sure myself (presuming you're debugging guest code?)
Scott Waye (Sep 25 2023 at 15:35):Yes, that's right. No problem, I can revert to printfs for these.
Scott Waye (Sep 25 2023 at 15:35):or copy to locals on the frame, those work fine
CryZe (Sep 26 2023 at 18:15):lldb / gdb seem to work well with the 13.0 release for me. However I've only been able to get them to work with wasm on Linux. Has anyone had any luck on Windows? (Our ecosystem is mostly comprised of Windows users, so a debugging workflow that works for them would be great)
Alex Crichton (Sep 26 2023 at 18:24):SingleAccretion on github may know more given PRs like this, but I've not done it myself
Scott Waye (Sep 26 2023 at 19:31):Thanks yes that env var is essential. LLDB works for me on Windows, modulo not being able to view c++ class statics. @CryZe I had to build wasmtime from source, the prebuilt binary didn't work for me.
Scott Waye (Sep 26 2023 at 19:33):lldb also works from VS Code for me with Rust on Windows, although I'm not sure I understand how to form all the command args properly for lldb with cargo
CryZe (Sep 26 2023 at 19:52):@Scott Waye I've tried the CodeLLDB extension on Windows and it does not pick up any wasm debug symbols, unlike the same extension on the same code on Linux. Are you using a different extension? Or none at all?
CryZe (Sep 26 2023 at 19:54):Wait, after trying it again right now. It totally does work... nvm then, thanks :D
Artem Kobzar (Oct 28 2024 at 09:35):Hi there. I'm Artem from the Kotlin/Wasm team. We started to play around with DWARF generating and the wasmtime debug described here: https://docs.wasmtime.dev/examples-debugging-native-debugger.html
I faced the problem of setting a breakpoint by file name and line number on a non-clang-generated DWARF.
I've minimized an example and just tried to use debug information generated by wasm-tools (https://github.com/bytecodealliance/wasm-tools) while parsing a WAT file and still, I have stopped by function name, but not by file name/line number.
Do you use the information provided by the .debug_line section, and (if yes), do you use some heuristics on it?
Alex Crichton (Oct 28 2024 at 15:10):I suspect this is a case where DWARF basically needs to look like what clang generates for gdb/lldb to understand it (similar to how in Rust we often have to look exactly like Clang to get optimizations to kick in). When I wrote the support for -g in wasm-tools I didn't test in Wasmtime other than doing things like addr2line operations. I'm certainly no dwarf expert myself so I suspect a section is missing or something like that.
Wasmtime should translate all the various DWARF sections as necessary, but my guess is that there's some missing link between function debug information and .debug_line (or something like that). I don't know enough about LLDB/GDB though to know which section is missing.
Alex Crichton (Oct 28 2024 at 15:11):If you find out though let me know and I can try to update the dwarf support in wasm-tools (which I realize may not be relevant for your exact use case but is probably useful to have anyway)
bjorn3 (Oct 29 2024 at 17:22):You need a DW_TAG_compile_unit which covers all functions in the line program (using DW_AT_ranges or DW_AT_low_pc + DW_AT_high_pc) and additionally a DW_AT_stmt_list pointing to the line program itself.
Ralph (Oct 29 2024 at 17:37):I like a person who knows their dwarf requirements
Last updated: Dec 23 2024 at 14:03 UTC