Draft: start to implement emscripten_return_address for UBSan support

[mrexodia]

This isn't really a pull request in the traditional sense, but I figure it will be easier to ask my question this way.

My goal is to compile a WASM executable with emscripten+UBSan (https://emscripten.org/docs/debugging/Sanitizers.html) and then run it in wasm3, showing a backtrace if anything is triggered.

I took the null-assign.c from the page:

int main(void) {
    int *a = 0;
    *a = 0;
}

Built it with the minimal UBSan runtime:

emcc null-assign.c -fsanitize=undefined -fsanitize-minimal-runtime -o null-assign.wasm -g

And I get null-assign.wasm.

I figured out that I need to set some preprocessor definitions to enable the call stack and trace output: -Dd_m3EnableStrace=2 -Dd_m3RecordBacktraces. Additionally I added my own -Dd_m3HasUBSan and implemented a stub emscripten_return_address (the function that the UBSan runtime needs).

Everything looks 'fine' from the trace (except obviously the 1234 value for the return address which triggers another check):

build\Debug>wasm3 null-assign.wasm
_start () {
  __wasm_call_ctors () {
    emscripten_stack_init () {
    }
  }
  __original_main () {
    __ubsan_handle_type_mismatch_minimal () {
      env!emscripten_return_address(0) { <native> } = 1234
      report_this_error(void*) (i32: 1234) {
      } = 1
      strlen (i32: 65560) {
      } = 21
      write (i32: 2, i32: 65560, i32: 21) {
ubsan: type-mismatch
        wasi_snapshot_preview1!fd_write(2, 65512, 1, 65508) { <native> } = 0
        __wasi_syscall_ret (i32: 0) {
        } = 0
      } = 21
    }
  } = 0
  exit (i32: 0) {
    dummy () {
    }
    libc_exit_fini () {
      dummy () {
      }
    }
    dummy () {
    }
    _Exit (i32: 0) {
      wasi_snapshot_preview1!proc_exit(0) { <native> } -> [trap] program called exit
Assertion failed at D:\CodeBlocks\wasm3\source\m3_core.c:556 : pcFound

The issue is at the end, it looks like it is not able to match the PC register back to an offset in the file. Any ideas why? I tried messing with the emscripten_return_address function signature but it doesn't appear to make a difference...