Attempting to build a small janet program for the web with emscripten

[xrd]

I'm trying to build a simple program for the web. Given that make emscripten seems to be removed, I'm trying to do this by hand.

I started with a simple janet.c

#include <janet.h>

int main(int argc, const char *argv[]) {
    // Initialize the virtual machine. Do this before any calls to Janet functions.
    janet_init();

    // Get the core janet environment. This contains all of the C functions in the core
    // as well as the code in src/boot/boot.janet.
    JanetTable *env = janet_core_env(NULL);

    // One of several ways to begin the Janet vm.
    janet_dostring(env, "(print `hello, world!`)", "main", NULL);

    // Use this to free all resources allocated by Janet.
    janet_deinit();
    return 0;
}

Running emcc -o test.html janet.c returns this:

$ emcc -o test.html janet.c 
janet.c:1:10: fatal error: 'janet.h' file not found
#include <janet.h>
         ^~~~~~~~~
1 error generated.
emcc: error: '/nix/store/nirxj3yfgqz4hjrbnfafqx6q7cv42pj9-emscripten-llvm-3.0.0/bin/clang -target wasm32-unknown-emscripten -DEMSCRIPTEN -fignore-exceptions -fvisibility=default -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr -D__EMSCRIPTEN_major__=3 -D__EMSCRIPTEN_minor__=0 -D__EMSCRIPTEN_tiny__=0 -D_LIBCPP_ABI_VERSION=2 -Werror=implicit-function-declaration -Xclang -iwithsysroot/include/SDL --sysroot=/nix/store/vvnjmasnk43318wcg7k8pzkx0ki6awh2-emscripten-3.0.0/share/emscripten/cache/sysroot -resource-dir=/nix/store/nirxj3yfgqz4hjrbnfafqx6q7cv42pj9-emscripten-llvm-3.0.0/lib/clang/13.0.1/ -idirafter/nix/store/vvnjmasnk43318wcg7k8pzkx0ki6awh2-emscripten-3.0.0/share/emscripten/cache/sysroot/include -iwithsysroot/include/c++/v1 -Xclang -iwithsysroot/include/compat janet.c -c -o /run/user/1000/emscripten_temp__d5wdz7q/janet_0.o' failed (returned 1)

Ok, so use the -I switch:

$ emcc -I/nix/store/d2d395908dfw2hl1lq7czf1ws8wky5p9-janet-1.21.2/include/janet  -o out.html janet.c error: undefined symbol: janet_core_env (referenced by top-level compiled C/C++ code)
warning: Link with `-s LLD_REPORT_UNDEFINED` to get more information on undefined symbols
warning: To disable errors for undefined symbols use `-s ERROR_ON_UNDEFINED_SYMBOLS=0`
warning: _janet_core_env may need to be added to EXPORTED_FUNCTIONS if it arrives from a system library
error: undefined symbol: janet_deinit (referenced by top-level compiled C/C++ code)
warning: _janet_deinit may need to be added to EXPORTED_FUNCTIONS if it arrives from a system library
error: undefined symbol: janet_dostring (referenced by top-level compiled C/C++ code)
warning: _janet_dostring may need to be added to EXPORTED_FUNCTIONS if it arrives from a system library
error: undefined symbol: janet_init (referenced by top-level compiled C/C++ code)
warning: _janet_init may need to be added to EXPORTED_FUNCTIONS if it arrives from a system library
Error: Aborting compilation due to previous errors
emcc: error: '/nix/store/knhxbwj2jaw2j3b3vj64j8jzxc0dwvja-nodejs-16.17.1/bin/node /nix/store/vvnjmasnk43318wcg7k8pzkx0ki6awh2-emscripten-3.0.0/share/emscripten/src/compiler.js /run/user/1000/tmpgssvd9pg.txt' failed (returned 1)

Looks like I need to link to a library so I can get those symbols? And, nm reports this symbol exists.

$ nm /nix/store/d2d395908dfw2hl1lq7czf1ws8wky5p9-janet-1.21.2/lib/libjanet.so | grep janet_core_env
000000000004fe90 T janet_core_env

So, add libjanet.so?

$ emcc -ljanet -L/nix/store/d2d395908dfw2hl1lq7czf1ws8wky5p9-janet-1.21.2/lib -I/nix/store/d2d395908dfw2hl1lq7czf1ws8wky5p9-janet-1.21.2/include/janet  -o out.html janet.c 
wasm-ld: error: unknown file type: meson-generated_.._janet.c.o
emcc: error: '/nix/store/nirxj3yfgqz4hjrbnfafqx6q7cv42pj9-emscripten-llvm-3.0.0/bin/wasm-ld -o out.wasm /nix/store/d2d395908dfw2hl1lq7czf1ws8wky5p9-janet-1.21.2/lib/libjanet.a -L/nix/store/d2d395908dfw2hl1lq7czf1ws8wky5p9-janet-1.21.2/lib /run/user/1000/emscripten_temp_2kcrm_kv/janet_0.o -L/nix/store/vvnjmasnk43318wcg7k8pzkx0ki6awh2-emscripten-3.0.0/share/emscripten/cache/sysroot/lib/wasm32-emscripten -lGL -lal -lhtml5 -lstubs-debug -lc -lcompiler_rt -lc++-noexcept -lc++abi-noexcept -ldlmalloc -lc_rt -lsockets -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr --import-undefined --strip-debug --export-if-defined=main --export-if-defined=emscripten_stack_get_end --export-if-defined=emscripten_stack_get_free --export-if-defined=emscripten_stack_init --export-if-defined=stackSave --export-if-defined=stackRestore --export-if-defined=stackAlloc --export-if-defined=__wasm_call_ctors --export-if-defined=fflush --export-if-defined=__errno_location --export-if-defined=__start_em_asm --export-if-defined=__stop_em_asm --export-table -z stack-size=5242880 --initial-memory=16777216 --no-entry --max-memory=16777216 --global-base=1024' failed (returned 1)

That looks weird, try to find that meson export...

$ nm /nix/store/d2d395908dfw2hl1lq7czf1ws8wky5p9-janet-1.21.2/lib/libjanet.so | grep meson

Nothing.

I don't know what to do now. Any suggestions?

By the way:

$ emcc -v
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 3.0.0-git
clang version 13.0.1
Target: wasm32-unknown-emscripten
Thread model: posix
InstalledDir: /nix/store/nirxj3yfgqz4hjrbnfafqx6q7cv42pj9-emscripten-llvm-3.0.0/bin

$ janet -v
1.21.2-release

[xrd]

On OSX:

% janet -v
1.27.0-3858b2e1

% emcc -v
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 3.1.35-git
clang version 17.0.0 (https://github.com/llvm/llvm-project.git 6865cff8ea8b07d9f2385fd92cecb422404f0f35)
Target: wasm32-unknown-emscripten
Thread model: posix
InstalledDir: /opt/homebrew/Cellar/emscripten/3.1.35/libexec/llvm/bin

% emcc -ljanet -L /usr/local/lib -I /usr/local/include/janet -o test.html janet.c 
emcc: warning: /usr/local/lib/libjanet.a: archive is missing an index; Use emar when creating libraries to ensure an index is created [-Wemcc]
emcc: warning: /usr/local/lib/libjanet.a: adding index [-Wemcc]
wasm-ld: error: /var/folders/bm/ygmxkgms1bq702315dsmcjbw0000gn/T/emscripten_temp_ujishdq6/janet_0.o: undefined symbol: janet_init
wasm-ld: error: /var/folders/bm/ygmxkgms1bq702315dsmcjbw0000gn/T/emscripten_temp_ujishdq6/janet_0.o: undefined symbol: janet_core_env
wasm-ld: error: /var/folders/bm/ygmxkgms1bq702315dsmcjbw0000gn/T/emscripten_temp_ujishdq6/janet_0.o: undefined symbol: janet_dostring
wasm-ld: error: /var/folders/bm/ygmxkgms1bq702315dsmcjbw0000gn/T/emscripten_temp_ujishdq6/janet_0.o: undefined symbol: janet_deinit
emcc: error: '/opt/homebrew/Cellar/emscripten/3.1.35/libexec/llvm/bin/wasm-ld -o test.wasm /usr/local/lib/libjanet.a -L/usr/local/lib /var/folders/bm/ygmxkgms1bq702315dsmcjbw0000gn/T/emscripten_temp_ujishdq6/janet_0.o -L/opt/homebrew/Cellar/emscripten/3.1.35/libexec/cache/sysroot/lib/wasm32-emscripten -lGL -lal -lhtml5 -lstubs-debug -lnoexit -lc-debug -ldlmalloc -lcompiler_rt -lc++-noexcept -lc++abi-debug-noexcept -lsockets -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr --allow-undefined-file=/var/folders/bm/ygmxkgms1bq702315dsmcjbw0000gn/T/tmp9w268o33.undefined --strip-debug --export-if-defined=main --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_argc_argv --export-if-defined=fflush --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=stackSave --export=stackRestore --export=stackAlloc --export=__errno_location --export=__get_temp_ret --export=__set_temp_ret --export=__wasm_call_ctors --export-table -z stack-size=65536 --initial-memory=16777216 --no-entry --max-memory=16777216 --stack-first' failed (returned 1)

[ianthehenry]

It seems like you're trying to get emscripten to link against your system libjanet, which was compiled for your native architecture and not for webassembly. I think you have to first recompile Janet itself with emcc and link against that artifact. Depending on how you installed Janet you might already have a copy of (Janet's) janet.c somewhere, or you might need to get it separately. (I've taken to vendoring these files in my repos, which is annoying -- I kinda wish janet.c was part of a standard Janet distribution for this reason.)

[xrd]

Ah, got it.

I'm loving your book by the way!

So, if I were to use your bauble studio project and build Janet with emcc using your scripts, I probably could build against that, right? I'm still a little overwhelmed by the scale of that project but perhaps I can pluck out artifacts if i can get it to all build.

[ianthehenry]

Yeah, that's... not a friendly place to start.

I think the only thing you need to do differently is to download the .c and .h files from here: https://github.com/janet-lang/janet/releases/tag/v1.27.0, and put them in a directory called janet. Then run:

emcc -I janet janet/janet.c your-actual-program.c

There's a little more to it afterwards because you need to then import and run the generated wasm from JavaScript, but that's not really Janet-specific.

This might actually be a better place to start:

• https://github.com/janet-lang/janet-lang.org/blob/master/Makefile
• https://github.com/janet-lang/janet-lang.org/blob/master/static/js/repl.js

That's how the repl on https://janet-lang.org is built. It's a bit simpler than Bauble/Toodle.studio.

[xrd]

Well, I tried the simple case (copying janet.[ch] into janet) and got this:

$ emcc  -I janet janet/janet.c mine.c  -o test.html
src/core/os.c:1498:13: error: implicit declaration of function 'timegm' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
        t = timegm(&t_info);
            ^
src/core/os.c:1498:13: note: did you mean 'time'?
/nix/store/vvnjmasnk43318wcg7k8pzkx0ki6awh2-emscripten-3.0.0/share/emscripten/cache/sysroot/include/time.h:53:8: note: 'time' declared here
time_t time (time_t *);
       ^
1 error generated.
emcc: error: '/nix/store/nirxj3yfgqz4hjrbnfafqx6q7cv42pj9-emscripten-llvm-3.0.0/bin/clang -target wasm32-unknown-emscripten -DEMSCRIPTEN -fignore-exceptions -fvisibility=default -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr -D__EMSCRIPTEN_major__=3 -D__EMSCRIPTEN_minor__=0 -D__EMSCRIPTEN_tiny__=0 -D_LIBCPP_ABI_VERSION=2 -Werror=implicit-function-declaration -Xclang -iwithsysroot/include/SDL --sysroot=/nix/store/vvnjmasnk43318wcg7k8pzkx0ki6awh2-emscripten-3.0.0/share/emscripten/cache/sysroot -resource-dir=/nix/store/nirxj3yfgqz4hjrbnfafqx6q7cv42pj9-emscripten-llvm-3.0.0/lib/clang/13.0.1/ -idirafter/nix/store/vvnjmasnk43318wcg7k8pzkx0ki6awh2-emscripten-3.0.0/share/emscripten/cache/sysroot/include -iwithsysroot/include/c++/v1 -Xclang -iwithsysroot/include/compat -Ijanet janet/janet.c -c -o /run/user/1000/emscripten_temp_p372z4ul/janet_0.o' failed (returned 1)

mine.c:

#include <janet.h>
#include <emscripten.h>

int main(int argc, const char *argv[]) {
    // Initialize the virtual machine. Do this before any calls to Janet functions.
    janet_init();

    // Get the core janet environment. This contains all of the C functions in the core
    // as well as the code in src/boot/boot.janet.
    JanetTable *env = janet_core_env(NULL);

    // One of several ways to begin the Janet vm.
    janet_dostring(env, "(print `hello, world!`)", "main", NULL);

    // Use this to free all resources allocated by Janet.
    janet_deinit();
    return 0;
}

[ianthehenry]

Hmm, that same example compiles fine for me on emscripten 3.1.24. Might need to update? Otherwise you could probably patch the source to get rid of it, if that's the only error -- looks like Janet only calls that in one place.

[xrd]

Yes! Upgrading emcc worked. Thanks so much for all your attention on this.