support _initialize export as well as __wasm_call_ctors

Per WebAssembly/tool-conventions#203 and recent LLVM and
wasi-libc changes, libraries may export an `_initialize` function instead of
`__wasm_call_ctors`, and we should call whichever one we find.  Note that we
expect to find at most one of the two, and will return an error if both are
found.

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

crates/wit-component/src/linking.rs

@@ -604,6 +604,14 @@ fn make_init_module(
             )));
         }
 
+        if metadata.has_ctors && metadata.has_initialize {
+            bail!(
+                "library {} exports both `__wasm_call_ctors` and `_initialize`; \
+                 expected at most one of the two",
+                metadata.name
+            );
+        }
+
         if metadata.has_ctors {
             ctor_calls.push(Ins::Call(add_function_import(
                 &mut imports,
@@ -613,6 +621,15 @@ fn make_init_module(
             )));
         }
 
+        if metadata.has_initialize {
+            ctor_calls.push(Ins::Call(add_function_import(
+                &mut imports,
+                metadata.name,
+                "_initialize",
+                thunk_ty,
+            )));
+        }
+
         if metadata.has_set_libraries {
             ctor_calls.push(Ins::I32Const(
                 i32::try_from(dl_openables.libraries_address).unwrap(),

crates/wit-component/src/linking/metadata.rs

@@ -199,6 +199,9 @@ pub struct Metadata<'a> {
     /// Whether this module exports `__wasm_call_ctors`
     pub has_ctors: bool,
 
+    /// Whether this module exports `_initialize`
+    pub has_initialize: bool,
+
     /// Whether this module exports `__wasm_set_libraries`
     pub has_set_libraries: bool,
 
@@ -303,6 +306,7 @@ impl<'a> Metadata<'a> {
             needed_libs: Vec::new(),
             has_data_relocs: false,
             has_ctors: false,
+            has_initialize: false,
             has_set_libraries: false,
             has_component_exports,
             env_imports: BTreeSet::new(),
@@ -491,6 +495,7 @@ impl<'a> Metadata<'a> {
                         match export.name {
                             "__wasm_apply_data_relocs" => result.has_data_relocs = true,
                             "__wasm_call_ctors" => result.has_ctors = true,
+                            "_initialize" => result.has_initialize = true,
                             "__wasm_set_libraries" => result.has_set_libraries = true,
                             _ => {
                                 let ty = match export.kind {

crates/wit-component/tests/components/error-link-duplicate-initializers/error.txt

@@ -0,0 +1 @@
+library foo exports both `__wasm_call_ctors` and `_initialize`; expected at most one of the two

crates/wit-component/tests/components/error-link-duplicate-initializers/lib-bar.wat

@@ -0,0 +1,12 @@
+(module
+  (@dylink.0
+    (mem-info (memory 0 4))
+    (needed "foo")
+  )
+  (type (func (param i32) (result i32)))
+  (import "env" "foo" (func $import_foo (type 0)))
+  (func $bar (type 0) (param i32) (result i32)
+    unreachable
+  )
+  (export "bar" (func $bar))
+)

crates/wit-component/tests/components/error-link-duplicate-initializers/lib-bar.wit

@@ -0,0 +1,3 @@
+package test:test;
+
+world lib-bar { }

crates/wit-component/tests/components/error-link-duplicate-initializers/lib-foo.wat

@@ -0,0 +1,21 @@
+(module
+  (@dylink.0
+    (mem-info (memory 0 4))
+    (needed "bar")
+  )
+  (type (func (param i32) (result i32)))
+  (type (func))
+  (import "test:test/test" "foo" (func $import_foo (type 0)))
+  (import "env" "foo" (func $import_foo2 (type 0)))
+  (import "env" "bar" (func $import_bar (type 0)))
+  (func $foo (type 0) (param i32) (result i32)
+    unreachable
+  )
+  (func $_initialize (type 1)
+    unreachable
+  )
+  (export "test:test/test#foo" (func $foo))
+  (export "foo" (func $foo))
+  (export "_initialize" (func $_initialize))
+  (export "__wasm_call_ctors" (func $_initialize))  
+)

crates/wit-component/tests/components/error-link-duplicate-initializers/lib-foo.wit

@@ -0,0 +1,10 @@
+package test:test;
+
+interface test {
+   foo: func(v: s32) -> s32;
+}
+
+world lib-foo {
+    import test;
+    export test;
+}