Reactor support. (#74)

* Add support for the Reactor model.

* Mark _activate and _start as wasm exports.

* Rename _activate to _initialize.

* Don't define `_fini`.

* Rename reactor-crt1.c to crt1-reactor.c.

basics/crt/crt1.c

@@ -3,6 +3,7 @@ extern int __original_main(void);
 extern void __prepare_for_exit(void);
 void _Exit(int) __attribute__((noreturn));
 
+__attribute__((export_name("_start")))
 void _start(void) {
     // The linker synthesizes this to call constructors.
     __wasm_call_ctors();

expected/wasm32-wasi/defined-symbols.txt

@@ -273,8 +273,8 @@ __xpg_strerror_r
 __year_to_secs
 _environ
 _exit
-_fini
 _flushlbf
+_initialize
 _start
 a64l
 abort

libc-bottom-half/crt/crt1-reactor.c

@@ -0,0 +1,7 @@
+extern void __wasm_call_ctors(void);
+
+__attribute__((export_name("_initialize")))
+void _initialize(void) {
+    // The linker synthesizes this to call constructors.
+    __wasm_call_ctors();
+}

libc-bottom-half/crt/crt1.c

@@ -3,6 +3,7 @@ extern void __wasm_call_ctors(void);
 extern int __original_main(void);
 extern void __prepare_for_exit(void);
 
+__attribute__((export_name("_start")))
 void _start(void) {
     // The linker synthesizes this to call constructors.
     __wasm_call_ctors();

libc-top-half/musl/src/exit/exit.c

@@ -10,9 +10,9 @@ static void dummy()
  * as a consequence of linking either __toread.c or __towrite.c. */
 weak_alias(dummy, __funcs_on_exit);
 weak_alias(dummy, __stdio_exit);
+#ifdef __wasilibc_unmodified_upstream // fini
 weak_alias(dummy, _fini);
 
-#ifdef __wasilibc_unmodified_upstream // fini
 extern weak hidden void (*const __fini_array_start)(void), (*const __fini_array_end)(void);
 
 static void libc_exit_fini(void)