symbolize_test: Add an indirection for getting the PC from function ptr.

Don't assume that function ptr == PC. Adds a redirection mechanism, GetPCFromFnPtr, and enables more test cases for Emscripten/Wasm.

On many (most?) platforms, the address of a function ptr is the same as its
Program Counter (PC) for the purpose of most things, including symbolization.

In Emscripten WebAssembly, the function ptr is just an index into a table of
functions. However, the name section maps function names to their literal
offsets into a Wasm binary. The WasmOffsetConverter is actually capable of both
indirections, so we can effectively go from function ptr to offset into the
binary (which is typically the "PC" for other Stack dumping things in Wasm,
including `emscripten_pc_get_function`).

More info: https://www.w3.org/TR/wasm-js-api-2/#exported-function-exotic-objects

Also fix Emscripten symbolize handling for `nullptr` now that we have tests for
that.

PiperOrigin-RevId: 546006678
Change-Id: I0d4015ca9035b004158451b36c933cad009184ba

1 files changed, 3 insertions, 0 deletions

diff --git a/absl/debugging/symbolize_emscripten.inc b/absl/debugging/symbolize_emscripten.inc
index c226c456..a0f344dd 100644
--- a/absl/debugging/symbolize_emscripten.inc
+++ b/absl/debugging/symbolize_emscripten.inc
@@ -50,6 +50,9 @@ bool Symbolize(const void* pc, char* out, int out_size) {
   if (!HaveOffsetConverter()) {
     return false;
   }
+  if (pc == nullptr || out_size <= 0) {
+    return false;
+  }
   const char* func_name = emscripten_pc_get_function(pc);
   if (func_name == nullptr) {
     return false;