fix JuliaLang#12444 (add magic and format version to beginning of .ji files)

Author: stevengj

src/dump.c

@@ -949,6 +949,15 @@ void jl_serialize_mod_list(ios_t *s)
     write_int32(s, 0);
 }
 
+// "magic" string and version header of .ji file
+const int JI_FORMAT_VERSION = 0;
+const char JI_MAGIC[] = "\373jli\r\n\032\n"; // based on PNG signature
+static void jl_serialize_header(ios_t *s)
+{
+    ios_write(s, JI_MAGIC, strlen(JI_MAGIC));
+    write_uint16(s, JI_FORMAT_VERSION);
+}
+
 // --- deserialize ---
 
 static jl_fptr_t jl_deserialize_fptr(ios_t *s)
@@ -1525,6 +1534,17 @@ int jl_deserialize_verify_mod_list(ios_t *s)
     }
 }
 
+static int jl_deserialize_header(ios_t *s)
+{
+    char magic[16];
+    size_t len = strlen(JI_MAGIC);
+    assert(len < 16);
+    ios_read(s, magic, len);
+    magic[len] = 0;
+    return (!strcmp(magic, JI_MAGIC) &&
+            read_uint16(s) == JI_FORMAT_VERSION);
+}
+
 jl_array_t *jl_module_init_order;
 
 static void jl_finalize_serializer(ios_t *f) {
@@ -1892,6 +1912,7 @@ DLLEXPORT int jl_save_incremental(const char *fname, jl_array_t *worklist)
         return 1;
     }
     serializer_worklist = worklist;
+    jl_serialize_header(&f);
     jl_serialize_mod_list(&f); // this can throw, keep it early (before any actual initialization)
 
     JL_SIGATOMIC_BEGIN();
@@ -1933,7 +1954,8 @@ static jl_array_t *_jl_restore_incremental(ios_t *f)
         ios_close(f);
         return NULL;
     }
-    if (!jl_deserialize_verify_mod_list(f)) {
+    if (!jl_deserialize_header(f) ||
+        !jl_deserialize_verify_mod_list(f)) {
         ios_close(f);
         return NULL;
     }