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, 1 insertions, 1 deletions

diff --git a/wasm2c/examples/fac/fac.h b/wasm2c/examples/fac/fac.h
index 6e36ada2..7700bc42 100644
--- a/wasm2c/examples/fac/fac.h
+++ b/wasm2c/examples/fac/fac.h
@@ -29,9 +29,9 @@ typedef struct Z_fac_instance_t {
   char dummy_member;
 } Z_fac_instance_t;
 
-void Z_fac_init_module(void);
 void Z_fac_instantiate(Z_fac_instance_t*);
 void Z_fac_free(Z_fac_instance_t*);
+wasm_rt_func_type_t Z_fac_get_func_type(uint32_t param_count, uint32_t result_count, ...);
 
 /* export: 'fac' */
 u32 Z_facZ_fac(Z_fac_instance_t*, u32);