+#ifdef _REENTRANT
+#include <stdatomic.h>
+#endif
#include <wasi/api.h>
extern void __wasm_call_ctors(void);
extern int __main_void(void);
extern void __wasm_call_dtors(void);
-// Commands should only be called once per instance. This simple check ensures
-// that the `_start` function isn't started more than once.
-static volatile int started = 0;
-
__attribute__((export_name("_start")))
void _start(void) {
- // Don't allow the program to be called multiple times.
+ // 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();
+ }
+#else
+ static volatile int started = 0;
if (started != 0) {
__builtin_trap();
}
started = 1;
+#endif
// The linker synthesizes this to call constructors.
__wasm_call_ctors();