-gz argument seems to enable debugging information

[jmcclellan-figma]

Please include the following in your bug report:

Version of emscripten/emsdk:
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 4.0.3 (a9651ff)
clang version 21.0.0git (https:/github.com/llvm/llvm-project 6dc41a639334b913e762f65410fcd14a722b137f)
Target: wasm32-unknown-emscripten
Thread model: posix
InstalledDir: ~/emsdk/upstream/bin

Failing command line in full:

emcc hello.cc -o hello.html -g0 -gz

Full link command and output with -v appended:

/wasm-ld -o hello.wasm /var/folders/fn/j37bx8dd6qx5_dcnlqgq110m0000gp/T/emscripten_temp_q01d0kcp/hello_0.o -L/Users/jmcclellan/emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten -L/Users/jmcclellan/emsdk/upstream/emscripten/src/lib -lGL-getprocaddr -lal -lhtml5 -lstubs-debug -lnoexit -lc-debug -ldlmalloc-debug -lcompiler_rt -lc++-noexcept -lc++abi-debug-noexcept -lsockets -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr /var/folders/fn/j37bx8dd6qx5_dcnlqgq110m0000gp/T/tmp9r7nvx20libemscripten_js_symbols.so --export=emscripten_stack_get_end --export=emscripten_stack_get_free --export=emscripten_stack_get_base --export=emscripten_stack_get_current --export=emscripten_stack_init --export=_emscripten_stack_alloc --export=__wasm_call_ctors --export=_emscripten_stack_restore --export-if-defined=__start_em_asm --export-if-defined=__stop_em_asm --export-if-defined=__start_em_lib_deps --export-if-defined=__stop_em_lib_deps --export-if-defined=__start_em_js --export-if-defined=__stop_em_js --export-if-defined=main --export-if-defined=__main_argc_argv --export-if-defined=fflush --export-table -z stack-size=65536 --no-growable-memory --initial-heap=16777216 --no-entry --stack-first --table-base=1

#include <iostream>

int main() { std::cout << "Hello world\n"; }

Based on experience from clang, I would have expected -gz to enable debug compression but not necessarily enable any debugging information. Instead, it seems to enable extra debug sections.

emcc hello.cc -o hello.html -g0 -gz

creates a wasm file that is 2.2mb

while

emcc hello.cc -o hello.html -g0

creates one that is 189kb.

[sbc100]

Emscripten doesn't support -gz but it looks like -g<anything> will enable debugging and superseed the previous -g flags. We should probably explicitly ignore -gz.