[clang] [CodeGen][ObjC] Initial WebAssembly Support for GNUstep (PR #169043)

[Derek Schuff via cfe-commits]

dschuff wrote:

@sbc100 I also re-read First Issue in OP, and it looks like (mangling aside) the underlying problem is that symbols are being exported that weren't intended to be in the first place. It looks like maybe OP is running into the issue of Emscripten's hack of EMSCRIPTEN_KEEPALIVE -> attribute("used") -> WASM_SYM_NO_STRIP which then implies WASM_SYM_EXPORTED. IIUC they want to keep these symbols from being stripped but don't want them exported. Normally these unused exports are not necessarily a problem, they are just extra binary size that can removed with metadce. But when they cause linker errors because they are invalid C then everything breaks. So landing https://github.com/emscripten-core/emscripten/issues/24825 will keep everything from breaking (we'd probably also want to suppress the warning), and it seems useful independently. But it might still be also useful to take another crack at the EMSCRIPTEN_KEEPALIVE problem. It seems sticky because there are likely users depending on the fact that attribute("used") causes exporting (although hopefully most are using EMSCRIPTEN_KEEPALIVE instead of directly). But there are probably other uses of attribute("used") that just want to prevent stripping, and we can't tell them apart. We could maybe just add 2 distinct attributes ("just-no-dead-strip" and "just-export-unless-dead") and deprecate "used" but keep it working ~forever. Not sure if there's a better way.

https://github.com/llvm/llvm-project/pull/169043