Add __wasix_init and __wasix_resume to support partial evaluation tools

expected/wasm32-wasi-threads/defined-symbols.txt

@@ -532,6 +532,8 @@ __wasilibc_tls_align
 __wasilibc_tls_size
 __wasilibc_unlinkat
 __wasilibc_utimens
+__wasix_init
+__wasix_resume
 __wasm_call_dtors
 __wasm_signal
 __wcscoll_l

expected/wasm32-wasi/defined-symbols.txt

@@ -538,6 +538,8 @@ __wasilibc_tls_align
 __wasilibc_tls_size
 __wasilibc_unlinkat
 __wasilibc_utimens
+__wasix_init
+__wasix_resume
 __wasm_call_dtors
 __wasm_signal
 __wcscoll_l

expected/wasm64-wasi/defined-symbols.txt

@@ -538,6 +538,8 @@ __wasilibc_tls_align
 __wasilibc_tls_size
 __wasilibc_unlinkat
 __wasilibc_utimens
+__wasix_init
+__wasix_resume
 __wasm_call_dtors
 __wasm_signal
 __wcscoll_l

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

@@ -7,27 +7,40 @@ extern void __wasm_call_ctors(void);
 extern int __main_void(void);
 extern void __wasm_call_dtors(void);
 
+// We use `volatile` here to prevent the store to `started` from being
+// sunk past any subsequent code, and to prevent any compiler from
+// optimizing based on the knowledge that `_start` is the program
+// entrypoint.
+#ifdef _REENTRANT
+static volatile _Atomic int __wasix_started = 0;
+static volatile _Atomic int __wasix_resumed = 0;
+#else
+static volatile int __wasix_started = 0;
+static volatile int __wasix_resumed = 0;
+#endif
+
 __attribute__((export_name("_start")))
 void _start(void) {
     // Commands should only be called once per instance. This simple check
     // ensures that the `_start` function isn't started more than once.
-    //
-    // We use `volatile` here to prevent the store to `started` from being
-    // sunk past any subsequent code, and to prevent any compiler from
-    // optimizing based on the knowledge that `_start` is the program
-    // entrypoint.
 #ifdef _REENTRANT
-    static volatile _Atomic int started = 0;
     int expected = 0;
-    if (!atomic_compare_exchange_strong(&started, &expected, 1)) {
-	__builtin_trap();
+    int resume_expected = 0;
+    if (!atomic_compare_exchange_strong(&__wasix_started, &expected, 1)) {
+        __builtin_trap();
+    }
+    if (!atomic_compare_exchange_strong(&__wasix_resumed, &resume_expected, 1)) {
+        __builtin_trap();
     }
 #else
-    static volatile int started = 0;
-    if (started != 0) {
-	__builtin_trap();
+    if (__wasix_started != 0) {
+        __builtin_trap();
+    }
+    __wasix_started = 1;
+    if (__wasix_resumed != 0) {
+        __builtin_trap();
     }
-    started = 1;
+    __wasix_resumed = 1;
 #endif
 
 #ifdef _REENTRANT
@@ -51,3 +64,61 @@ void _start(void) {
         __wasi_proc_exit(r);
     }
 }
+
+// This function acts as the top "half" of _start, up until the call to
+// __main_void. This is useful when a module needs to do initialization
+// separately, e.g. when using partial evaluation tools. When used with
+// __wasix_resume, they perform the same logic as calling _start once.
+__attribute__((export_name("__wasix_init")))
+void __wasix_init(void) {
+#ifdef _REENTRANT
+    int expected = 0;
+    if (!atomic_compare_exchange_strong(&__wasix_started, &expected, 1)) {
+	__builtin_trap();
+    }
+#else
+    if (__wasix_started != 0) {
+        __builtin_trap();
+    }
+    __wasix_started = 1;
+#endif
+
+#ifdef _REENTRANT
+	__wasi_init_tp();
+#endif
+
+    __wasm_call_ctors();
+}
+
+// This is the bottom "half" of _start, which can be called after
+// __wasix_init to continue executing the module normally. This
+// function also checks the value of __wasix_started to make sure
+// __wasix_init was called beforehand.
+__attribute__((export_name("__wasix_resume")))
+void __wasix_resume(void) {
+#ifdef _REENTRANT
+    if (atomic_load(&__wasix_started) != 1) {
+        __builtin_trap();
+    }
+    int expected = 0;
+    if (!atomic_compare_exchange_strong(&__wasix_resumed, &expected, 1)) {
+	__builtin_trap();
+    }
+#else
+    if (__wasix_started != 1) {
+        __builtin_trap();
+    }
+    if (__wasix_resumed != 0) {
+        __builtin_trap();
+    }
+    __wasix_resumed = 1;
+#endif
+
+    int r = __main_void();
+
+    __wasm_call_dtors();
+
+    if (r != 0) {
+        __wasi_proc_exit(r);
+    }
+}