wasm2c: serialize types at wasm2c-time (#2120)

This makes wasm2c serialize each function type, rather than registering
function types at module-initialization time. The serialized function
type is the SHA-256 of the mangled param and result types (with a space
between params and results).

At runtime in call_indirect, a known (immediate) function type is
compared against the function type stored in a funcref structure. For
call_indirects to functions local to the module, or for any
call_indirect when the toolchain merges string constants across
compilation units (generally, GCC and clang), this can be done by
comparing the pointers to each function type. Otherwise, the actual
32-byte values are compared.

The function type IDs can be looked up at runtime with
`Z_[modname]_get_func_type`, which matches the API from
`wasm_rt_register_func_type`. A new `callback` example demos this.

wasm2c does the SHA-256 either by linking against libcrypto or, if not
available or if requested via `cmake -DUSE_INTERNAL_SHA256=ON`, by using
a vendored (header-only) PicoSHA2. There is no runtime dependency on
SHA-256 in the wasm2c runtime or generated modules.

This eliminates the last of the per-module state, so this commit also removes
the [modname]_init_module() function and the s_module_initialized bool.

1 files changed, 0 insertions, 4 deletions

diff --git a/wasm2c/examples/fac/main.c b/wasm2c/examples/fac/main.c
index 30bf5d0a..37593f6e 100644
--- a/wasm2c/examples/fac/main.c
+++ b/wasm2c/examples/fac/main.c
@@ -17,10 +17,6 @@ int main(int argc, char** argv) {
   /* Initialize the Wasm runtime. */
   wasm_rt_init();
 
-  /* Initialize the `fac` module (this registers the module's function types in
-   * a global data structure) */
-  Z_fac_init_module();
-
   /* Declare an instance of the `fac` module. */
   Z_fac_instance_t instance;