1 files changed, 20 insertions, 3 deletions

diff --git a/src/lj_obj.h b/src/lj_obj.h
index 9101f053..cebeda9b 100644
--- a/src/lj_obj.h
+++ b/src/lj_obj.h
@@ -315,7 +315,7 @@ typedef struct GCstr {
 /* Userdata object. Payload follows. */
 typedef struct GCudata {
   GCHeader;
-  uint8_t unused1;
+  uint8_t udtype;       /* Userdata type. */
   uint8_t unused2;
   GCRef env;            /* Should be at same offset in GCfunc. */
   MSize len;            /* Size of payload. */
@@ -323,6 +323,13 @@ typedef struct GCudata {
   uint32_t align1;      /* To force 8 byte alignment of the payload. */
 } GCudata;
 
+/* Userdata types. */
+enum {
+  UDTYPE_USERDATA,      /* Regular userdata. */
+  UDTYPE_IO_FILE,       /* I/O library FILE. */
+  UDTYPE__MAX
+};
+
 #define uddata(u)       ((void *)((u)+1))
 #define sizeudata(u)    (sizeof(struct GCudata)+(u)->len)
 
@@ -496,7 +503,17 @@ MMDEF(MMENUM)
   MM_FAST = MM_eq
 } MMS;
 
-#define BASEMT_MAX      ((~LJ_TNUMX)+1)
+/* GC root IDs. */
+typedef enum {
+  GCROOT_BASEMT,        /* Metatables for base types. */
+  GCROOT_BASEMT_NUM = ~LJ_TNUMX,  /* Last base metatable. */
+  GCROOT_IO_INPUT,      /* Userdata for default I/O input file. */
+  GCROOT_IO_OUTPUT,     /* Userdata for default I/O output file. */
+  GCROOT__MAX
+} GCRootID;
+
+#define basemt_it(g, it)        ((g)->gcroot[GCROOT_BASEMT+~(it)])
+#define basemt_obj(g, o)        ((g)->gcroot[GCROOT_BASEMT+itypemap(o)])
 
 typedef struct GCState {
   MSize total;          /* Memory currently allocated. */
@@ -544,7 +561,7 @@ typedef struct global_State {
   volatile int32_t vmstate;  /* VM state or current JIT code trace number. */
   GCRef jit_L;          /* Current JIT code lua_State or NULL. */
   MRef jit_base;        /* Current JIT code L->base. */
-  GCRef basemt[BASEMT_MAX];  /* Metatables for base types. */
+  GCRef gcroot[GCROOT__MAX];  /* GC roots. */
   GCRef mmname[MM_MAX]; /* Array holding metamethod names. */
 } global_State;