[Lldb-commits] [lldb] [lldb] Implement WebAssembly debugging (PR #77949)

[Paolo Severini via lldb-commits]

paolosevMSFT wrote:

> > But currently a simple gdb-remote [:] does not enable the "wasm' plugin. Is there a way to detect that we are debugging WebAssembly at connect time?
> 
> Tracing down from `platform connect <no plugin option>`, I get to `Process::FindPlugin`, which creates a process of all the registered types then asks that process if it can debug that target.
> 
> Though, a lot of them just return true and you already have:
> 
> ```
> bool ProcessWasm::CanDebug(lldb::TargetSP target_sp,
>                            bool plugin_specified_by_name) {
> ```
> 
> So I wonder if some other plugin is saying "yes I can debug this" before the wasm plugin has been asked. We must register the plugins in some order but not sure where that is done.

What happens now is that there is a `ProcessGDBRemote` that registers for `gdb-remote` and it is returned by `Process::FindPlugin`. Then there is the new `ProcessWasm` which might also register for the same `gdb-remote` maybe.
But the problem is that at the moment when we start the connection we do not know that we are connecting to a Wasm target.

Here, with the following call stack, `target_sp->m_arch` is still not initialized:
```
>	liblldb.dll!lldb_private::process_gdb_remote::ProcessGDBRemote::CreateInstance(std::shared_ptr<lldb_private::Target> target_sp, std::shared_ptr<lldb_private::Listener> listener_sp, const lldb_private::FileSpec * crash_file_path, bool can_connect) Line 201	C++
 	liblldb.dll!lldb_private::Process::FindPlugin(std::shared_ptr<lldb_private::Target> target_sp, llvm::StringRef plugin_name, std::shared_ptr<lldb_private::Listener> listener_sp, const lldb_private::FileSpec * crash_file_path, bool can_connect) Line 382	C++
 	liblldb.dll!lldb_private::Target::CreateProcess(std::shared_ptr<lldb_private::Listener> listener_sp, llvm::StringRef plugin_name, const lldb_private::FileSpec * crash_file, bool can_connect) Line 215	C++
 	liblldb.dll!lldb_private::Platform::DoConnectProcess(llvm::StringRef connect_url, llvm::StringRef plugin_name, lldb_private::Debugger & debugger, lldb_private::Stream * stream, lldb_private::Target * target, lldb_private::Status & error) Line 1948	C++
```

This is why I introduced a new command `wasm`.

https://github.com/llvm/llvm-project/pull/77949