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, 7 insertions, 2 deletions

diff --git a/test/spec-wasm2c-prefix.c b/test/spec-wasm2c-prefix.c
index b9ba0934..c3c6e500 100644
--- a/test/spec-wasm2c-prefix.c
+++ b/test/spec-wasm2c-prefix.c
@@ -194,10 +194,15 @@ static bool is_equal_wasm_rt_externref_t(wasm_rt_externref_t x,
   return x == y;
 }
 
+static inline bool is_equal_wasm_rt_func_type_t(const wasm_rt_func_type_t a,
+                                                const wasm_rt_func_type_t b) {
+  return (a == b) || (a && b && !memcmp(a, b, 32));
+}
+
 static bool is_equal_wasm_rt_funcref_t(wasm_rt_funcref_t x,
                                        wasm_rt_funcref_t y) {
-  return (x.func_type == y.func_type) && (x.func == y.func) &&
-         (x.module_instance == y.module_instance);
+  return is_equal_wasm_rt_func_type_t(x.func_type, y.func_type) &&
+         (x.func == y.func) && (x.module_instance == y.module_instance);
 }
 
 wasm_rt_externref_t spectest_make_externref(uintptr_t x) {