Hi,
Is there a method for importing functions from the Web Assembly runtime when writing C? I know Emscripten has support for calling JS functions from C code, but I was wondering if there’s an easy way to do this without Emscripten (pure Clang)?
Best,
Ved
Hi Ved,
Yes, the trick is to declare the functions you want to import in your C source, then pass the --allow-undefined flag to wasm-ld when linking your wasm module. Here’s a complete example:
hello.c:
int print_int(int x);
int do_work(int x) {
print_int(x);
return x;
}
clang -target wasm32 -c hello.c -o hello.o
wasm-ld hello.o -o hello.wasm --no-entry --allow-undefined --export=do_work
This will give you a wasm module that imports function “env” “print_int” and exports function “do_work”. Note that Wasm uses a two-level namespace for imports, but the first level will always be “env” unless you annotate the function declaration with __attribute__((import_module("my_other_namespace"))).
Best,
Thomas