When implementing the WebAssembly Process Plugin, I initially added
WasmGDBRemoteRegisterContext as a placeholder in the UnwindWasm TU.
After implementing RegisterContextWasm (#151056), I forgot to switch
over to the new implementation. This meant we were using the wrong
register context for all frames, except frame 0. The register context
deals with the virtual registers, so this only becomes an issue when
trying to evaluate a `DW_OP_WASM_location`, which is why this went
unnoticed.
This PR removes the WasmGDBRemoteRegisterContext placeholder and updates
UnwindWasm to use RegisterContextWasm instead for all frames.
In terms of testing, I considered updating TestWasm but that would
require adding even more state to the already complicated GDB stub. This
doesn't scale and my focus over the next weeks/months will be coming up
with a comprehensive testing strategy that involves running (a subset of
the) API tests under a Wasm runtime, which will cover this and much
more.
rdar://159297244
Extend support in LLDB for WebAssembly. This PR adds a new Process
plugin (ProcessWasm) that extends ProcessGDBRemote for WebAssembly
targets. It adds support for WebAssembly's memory model with separate
address spaces, and the ability to fetch the call stack from the
WebAssembly runtime.
I have tested this change with the WebAssembly Micro Runtime (WAMR,
https://github.com/bytecodealliance/wasm-micro-runtime) which implements
a GDB debug stub and supports the qWasmCallStack packet.
```
(lldb) process connect --plugin wasm connect://localhost:4567
Process 1 stopped
* thread #1, name = 'nobody', stop reason = trace
frame #0: 0x40000000000001ad
wasm32_args.wasm`main:
-> 0x40000000000001ad <+3>: global.get 0
0x40000000000001b3 <+9>: i32.const 16
0x40000000000001b5 <+11>: i32.sub
0x40000000000001b6 <+12>: local.set 0
(lldb) b add
Breakpoint 1: where = wasm32_args.wasm`add + 28 at test.c:4:12, address = 0x400000000000019c
(lldb) c
Process 1 resuming
Process 1 stopped
* thread #1, name = 'nobody', stop reason = breakpoint 1.1
frame #0: 0x400000000000019c wasm32_args.wasm`add(a=<unavailable>, b=<unavailable>) at test.c:4:12
1 int
2 add(int a, int b)
3 {
-> 4 return a + b;
5 }
6
7 int
(lldb) bt
* thread #1, name = 'nobody', stop reason = breakpoint 1.1
* frame #0: 0x400000000000019c wasm32_args.wasm`add(a=<unavailable>, b=<unavailable>) at test.c:4:12
frame #1: 0x40000000000001e5 wasm32_args.wasm`main at test.c:12:12
frame #2: 0x40000000000001fe wasm32_args.wasm
```
This PR is based on an unmerged patch from Paolo Severini:
https://reviews.llvm.org/D78801. I intentionally stuck to the
foundations to keep this PR small. I have more PRs in the pipeline to
support the other features/packets.
My motivation for supporting Wasm is to support debugging Swift compiled
to WebAssembly:
https://www.swift.org/documentation/articles/wasm-getting-started.html
