symblib: expose API for single point lookups

[florianl]

Implement a trait with the API for Go executables that got introduced with #346 and expose this trait as C API.

Go programm that uses this Rust API via the C FFI

	executablePath := C.CString("/.../...")
	defer C.free(unsafe.Pointer(executablePath))
	addr := uint64(0xc0ffee)

	var goRuntime *C.SymblibPointResolver

	status := C.symblib_goruntime_new(executablePath, &goRuntime)
	if status != C.SYMBLIB_OK {
		fmt.Fprintf(os.Stderr, "Failed to create SymblibGoRuntime: %d\n", status)
		return
	}
	defer C.symblib_goruntime_free(goRuntime)

	var symbols *C.SymblibSlice_SymblibResolvedSymbol
	defer C.symblib_slice_symblibresolved_symbol_free(symbols)

	status = C.symblib_point_resolver_symbols_for_pc(goRuntime, C.uint64_t(addr), &symbols)
	if status != C.SYMBLIB_OK {
		fmt.Fprintf(os.Stderr, "Failed to get information for 0x%x: %d\n",
			addr, status)
		return
	}

	// Access resolved symbols
	symbolsSlice := unsafe.Slice((*C.SymblibResolvedSymbol)(unsafe.Pointer(symbols.data)), symbols.len)
	for _, sym := range symbolsSlice {
		fmt.Printf("%s\n\t%s@%d\n",
			C.GoString(sym.function_name),
			C.GoString(sym.file_name),
			uint32(sym.line_number),
		)

	}

[athre0z]

I think you can break here after finding the first one, and turn source_files into Option<String> instead. I don't think that a symbol can have more than one filename?

[florianl]

Don't remember exactly why I went with Vec<_> instead of Option<_> for files and line numbers. Dropped this approach and followed the suggestion with a73f6f8.

[athre0z]

LGTM, thank you for tackling this! :)

[christos68k]

No need to mention Go here as there's nothing specific to Go, it can be called from any language that can interface with C APIs.

Suggested change

	// Create a new SymblibPointResolver handler from a Go executable.
	// Creates a new SymblibPointResolver handler.

[florianl]

Resolved with 9025013

[athre0z]

I think this was a misunderstanding? The function's doc comment referred to the sort of executable that the point resolver can symbolize, not the language that this function can be called from?