jit_stream_mmap: toggle W^X around the mmap size-header write

CHANGELOG.md

@@ -70,6 +70,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fixed several underallocation issues that could trigger data corruption on `binary:replace`, `zlib:compress` and bsd socket recv code.
 - Fixed a bug where `catch` would raise on regular atom results
 - Fixed ESP32 socket driver holding the global socket-list lock across blocking TCP connects, leaking the port on connect failure, losing concurrent `accept` waiters, leaking `netbuf` on receive error paths, and a recycled-`netconn` race between socket close and the event handler
+- Fixed a JIT crash (`EXC_BAD_ACCESS`/SIGBUS) on Apple Silicon
 
 ## [0.7.0-alpha.1] - 2026-04-06
 

src/platforms/generic_unix/lib/jit_stream_mmap.c

@@ -89,7 +89,13 @@ static term nif_jit_stream_mmap_new(Context *ctx, int argc, term argv[])
 
     // Write the total mmap size into the header so sys_release_native_code
     // can recover it (it reads *(size_t *)(entry_point - sizeof(size_t))).
+#if HAVE_PTHREAD_JIT_WRITE_PROTECT_NP
+    pthread_jit_write_protect_np(0);
+#endif
     *((size_t *) addr) = total;
+#if HAVE_PTHREAD_JIT_WRITE_PROTECT_NP
+    pthread_jit_write_protect_np(1);
+#endif
 
     // Return a resource object
     struct JITStreamMMap *js = enif_alloc_resource(jit_stream_mmap_resource_type, sizeof(struct JITStreamMMap));