Emscripten SDL Compilation faliure - c

Question

I'm new to emscripten; several days ago I've downloaded it just to try to make a port of a game to JS.
Anyway, after some steps, I'm having this issue now (on Ubuntu 16.04 STL).
By following build steps here, first of all, I've set environment variables with
source ./emsdk_env.sh and then I've tried to configure the project with emconfigure ./configure in the project directory. When checking for tools emscripten needs, I've got this error:
checking for SDL... no
configure: error: Package requirements (sdl2 >= 2.0.1) were not met:
No package 'sdl2' found
Consider adjusting the PKG_CONFIG_PATH environment variable if you
installed software in a non-standard prefix.
Alternatively, you may set the environment variables SDL_CFLAGS
and SDL_LIBS to avoid the need to call pkg-config.
See the pkg-config man page for more details.
ERROR:root:Configure step failed with non-zero return code 1! Command line: ['./configure'] at ...
So I've tried to set that variable with the following command:
export PKG_CONFIG_PATH=/usr/lib/x86_64-linux-gnu/pkgconfig/
This is where actually sdl2.pc is located on my machine, but it didn't help.
So then I've set the following variables that emconfigure needed:
export SDL_PATH=/home/ustym/Documents/Projects/emsdk/emscripten/1.37.38/system/include/SDL/SDL.h
export SDL_LIBS=/home/ustym/Documents/Projects/emsdk/emscripten/1.37.38/system/include/SDL/SDL.h
export SDL_CFLAGS=/home/ustym/Documents/Projects/emsdk/emscripten/1.37.38/system/include/SDL/SDL.h
export SDLNET_LIBS=/home/ustym/Documents/Projects/emsdk/emscripten/1.37.38/system/include/SDL/SDL.h
export SDLNET_CFLAGS=/home/ustym/Documents/Projects/emsdk/emscripten/1.37.38/system/include/SDL/SDL.h
export SDLMIXER_LIBS=/home/ustym/Documents/Projects/emsdk/emscripten/1.37.38/system/include/SDL/SDL.h
export SDLMIXER_CFLAGS=/home/ustym/Documents/Projects/emsdk/emscripten/1.37.38/system/include/SDL/SDL.h
and relaunched emconfigure ./configure which has completed well.
So the next step is emmake make that gives me the following error:
make all-recursive
make[1]: Entering directory '/home/ustym/Documents/Projects/chocolate-doom-3.0.0'
Making all in textscreen
make[2]: Entering directory '/home/ustym/Documents/Projects/chocolate-doom-3.0.0/textscreen'
Making all in fonts
make[3]: Entering directory '/home/ustym/Documents/Projects/chocolate-doom-3.0.0/textscreen/fonts'
make[3]: Nothing to be done for 'all'.
make[3]: Leaving directory '/home/ustym/Documents/Projects/chocolate-doom-3.0.0/textscreen/fonts'
Making all in .
make[3]: Entering directory '/home/ustym/Documents/Projects/chocolate-doom-3.0.0/textscreen'
CC txt_conditional.o
Traceback (most recent call last):
File "/home/ustym/Documents/Projects/emsdk/emscripten/1.37.38/emcc", line 11, in <module>
python_selector.run(__file__)
File "/home/ustym/Documents/Projects/emsdk/emscripten/1.37.38/tools/python_selector.py", line 38, in run
sys.exit(run_by_import(filename, main) if on_allowed_version() else run_by_subprocess(filename))
File "/home/ustym/Documents/Projects/emsdk/emscripten/1.37.38/tools/python_selector.py", line 13, in run_by_import
return getattr(importlib.import_module(os.path.basename(filename)), main)()
File "/home/ustym/Documents/Projects/emsdk/emscripten/1.37.38/emcc.py", line 1345, in run
assert header.endswith(HEADER_ENDINGS), 'if you have one header input, we assume you want to precompile headers, and cannot have source files or other inputs as well: ' + str(headers) + ' : ' + header
AssertionError: if you have one header input, we assume you want to precompile headers, and cannot have source files or other inputs as well: ['/home/ustym/Documents/Projects/emsdk/emscripten/1.37.38/system/include/SDL/SDL.h', 'txt_conditional.c'] : txt_conditional.c
Makefile:447: recipe for target 'txt_conditional.o' failed
make[3]: *** [txt_conditional.o] Error 1
make[3]: Leaving directory '/home/ustym/Documents/Projects/chocolate-doom-3.0.0/textscreen'
Makefile:467: recipe for target 'all-recursive' failed
make[2]: *** [all-recursive] Error 1
make[2]: Leaving directory '/home/ustym/Documents/Projects/chocolate-doom-3.0.0/textscreen'
Makefile:585: recipe for target 'all-recursive' failed
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory '/home/ustym/Documents/Projects/chocolate-doom-3.0.0'
Makefile:438: recipe for target 'all' failed
make: *** [all] Error 2
that means, I assume, that SDL_PATH, SDL_LIBS, SDL_CFLAGS... variables weren't set correctly. Or maybe I just need to precompile that headers in the SDL directory.
One last thing: if I skip setting SDL variables and the configuration step and just launch emmake make, the compilation goes well, but then, emcc command gives me
WARNING:root: .o is not valid LLVM bitcode
for all generated .o files. And that actually makes sense.
So I'm pretty stuck here. Somebody can tell me how to set correctly PKG_CONFIG_PATH for emscripten or if i really need to precompile those headers in the SDL directory? Thanks!

Answer 1

First of all, setting PKG_CONFIG_PATH, include or, even worse, library directories (-I and -L) to host libraries' ones looks like awful idea to me: Emscripten object files contain LLVM bitcode (and not host machine code), its .so files AFAIK contain bitcode as well. It is that bitcode that gets translated to JS, not host machine code. So you need to build your program's dependencies with Emscripten by yourself (and should most probably not install them to the host system). Fortunately, there are some official Emscripten ports (see here) for details.
Emscripten has its own implementation of SDL v1 (that you probably tried to use manually), but your program seems to require SDL2. Good news: you probably just need to pass -s USE_SDL=2 to CFLAGS and LDFLAGS when configureing (see later on the link above for information on SDL2 port). Bad news: something may not be fully ported. But I successfully used it to some extent.
When you have configured on host and make with emmake you probably had compiler paths among other parameters adjusted by emconfigure and emmake already baked into generated Makefile by ./configure not controlled by emconfigure, so host gcc/clang just generated machine code.