How to compile longjmp using emcc? - c

Question

I'm trying to diagnose a linker issue with emcc. I've got it down to the following file:
#include <setjmp.h>
jmp_buf error;
int main(int argc, char *argv[]) {
int n = setjmp(error);
if (n)
return n;
longjmp(error, 33);
return 0;
}
When compiled with gcc, this file produces an a.out that exits with code 33 as expected. But when compiled with emcc, it fails at the linking step, with this error:
nr#homedog ~/s/c [1]> emcc -s LLD_REPORT_UNDEFINED longjmp.c
error: undefined symbol: __invoke_void_$struct___jmp_buf_tag*_i32 (referenced by top-level compiled C/C++ code)
warning: To disable errors for undefined symbols use `-s ERROR_ON_UNDEFINED_SYMBOLS=0`
warning: ___invoke_void_$struct___jmp_buf_tag*_i32 may need to be added to EXPORTED_FUNCTIONS if it arrives from a system library
error: undefined symbol: emscripten_longjmp_jmpbuf (referenced by top-level compiled C/C++ code)
warning: _emscripten_longjmp_jmpbuf may need to be added to EXPORTED_FUNCTIONS if it arrives from a system library
Adding it to EXPORTED_FUNCTIONS results instead in this error:
wasm-ld: error: symbol exported via --export not found: emscripten_longjmp_jmpbuf
What do I need to do to compile this file?
I am running Debian stable (bullseye) with Emscripten version 2.0.12.
ETA: emcc reports versions as follows:
nr#homedog ~/s/c [1]> emcc -v
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 2.0.12
Debian clang version 11.0.1-2
Target: wasm32-unknown-emscripten
Thread model: posix
InstalledDir: /usr/bin

Answer 1

It looks like you have a mismatched llvm (clang) and emscripten versions. We recommend using emsdk to install all correct dependencies (how are you install them?). If you don't want use emsdk you will need to build llvm from source at the correct revision.
Your example works find with the latest version of emscripten:
$ emcc -v
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 2.0.29-git (6e9e10d3f78eb249bf09922a23e19c3f81a86d0f)
...
$ emcc -s LLD_REPORT_UNDEFINED setjmp.c