diff --git a/src/Makefile b/src/Makefile
index c99d8577..84f9d42f 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -358,7 +358,7 @@ LJLIB_O= lib_base.o lib_math.o lib_bit.o lib_string.o lib_table.o \
 LJLIB_C= $(LJLIB_O:.o=.c)
 
 LJCORE_O= lj_gc.o lj_err.o lj_char.o lj_bc.o lj_obj.o \
-	  lj_str.o lj_tab.o lj_func.o lj_udata.o lj_meta.o \
+	  lj_str.o lj_tab.o lj_func.o lj_udata.o lj_meta.o lj_debug.o \
 	  lj_state.o lj_dispatch.o lj_vmevent.o lj_vmmath.o lj_api.o \
 	  lj_lex.o lj_parse.o \
 	  lj_ir.o lj_opt_mem.o lj_opt_fold.o lj_opt_narrow.o \
diff --git a/src/Makefile.dep b/src/Makefile.dep
index d3dec2be..5e7f11dc 100644
--- a/src/Makefile.dep
+++ b/src/Makefile.dep
@@ -13,9 +13,9 @@ buildvm_peobj.o: buildvm_peobj.c buildvm.h lj_def.h lua.h luaconf.h \
 lib_aux.o: lib_aux.c lua.h luaconf.h lauxlib.h lj_obj.h lj_def.h \
  lj_arch.h lj_err.h lj_errmsg.h lj_state.h lj_lib.h lj_alloc.h
 lib_base.o: lib_base.c lua.h luaconf.h lauxlib.h lualib.h lj_obj.h \
- lj_def.h lj_arch.h lj_gc.h lj_err.h lj_errmsg.h lj_str.h lj_tab.h \
- lj_meta.h lj_state.h lj_ctype.h lj_cconv.h lj_bc.h lj_ff.h lj_ffdef.h \
- lj_dispatch.h lj_jit.h lj_ir.h lj_char.h lj_lib.h lj_libdef.h
+ lj_def.h lj_arch.h lj_gc.h lj_err.h lj_errmsg.h lj_debug.h lj_str.h \
+ lj_tab.h lj_meta.h lj_state.h lj_ctype.h lj_cconv.h lj_bc.h lj_ff.h \
+ lj_ffdef.h lj_dispatch.h lj_jit.h lj_ir.h lj_char.h lj_lib.h lj_libdef.h
 lib_bit.o: lib_bit.c lua.h luaconf.h lauxlib.h lualib.h lj_obj.h lj_def.h \
  lj_arch.h lj_err.h lj_errmsg.h lj_str.h lj_lib.h lj_libdef.h
 lib_debug.o: lib_debug.c lua.h luaconf.h lauxlib.h lualib.h lj_obj.h \
@@ -30,9 +30,10 @@ lib_io.o: lib_io.c lua.h luaconf.h lauxlib.h lualib.h lj_obj.h lj_def.h \
  lj_trace.h lj_jit.h lj_ir.h lj_dispatch.h lj_bc.h lj_traceerr.h lj_lib.h \
  lj_libdef.h
 lib_jit.o: lib_jit.c lua.h luaconf.h lauxlib.h lualib.h lj_arch.h \
- lj_obj.h lj_def.h lj_err.h lj_errmsg.h lj_str.h lj_tab.h lj_bc.h lj_ir.h \
- lj_jit.h lj_ircall.h lj_iropt.h lj_target.h lj_target_*.h \
- lj_dispatch.h lj_vm.h lj_vmevent.h lj_lib.h luajit.h lj_libdef.h
+ lj_obj.h lj_def.h lj_err.h lj_errmsg.h lj_debug.h lj_str.h lj_tab.h \
+ lj_bc.h lj_ir.h lj_jit.h lj_ircall.h lj_iropt.h lj_target.h \
+ lj_target_*.h lj_dispatch.h lj_vm.h lj_vmevent.h lj_lib.h luajit.h \
+ lj_libdef.h
 lib_math.o: lib_math.c lua.h luaconf.h lauxlib.h lualib.h lj_obj.h \
  lj_def.h lj_arch.h lj_lib.h lj_vm.h lj_libdef.h
 lib_os.o: lib_os.c lua.h luaconf.h lauxlib.h lualib.h lj_obj.h lj_def.h \
@@ -47,9 +48,9 @@ lib_table.o: lib_table.c lua.h luaconf.h lauxlib.h lualib.h lj_obj.h \
  lj_libdef.h
 lj_alloc.o: lj_alloc.c lj_def.h lua.h luaconf.h lj_arch.h lj_alloc.h
 lj_api.o: lj_api.c lj_obj.h lua.h luaconf.h lj_def.h lj_arch.h lj_gc.h \
- lj_err.h lj_errmsg.h lj_str.h lj_tab.h lj_func.h lj_udata.h lj_meta.h \
- lj_state.h lj_bc.h lj_frame.h lj_trace.h lj_jit.h lj_ir.h lj_dispatch.h \
- lj_traceerr.h lj_vm.h lj_lex.h lj_parse.h
+ lj_err.h lj_errmsg.h lj_debug.h lj_str.h lj_tab.h lj_func.h lj_udata.h \
+ lj_meta.h lj_state.h lj_bc.h lj_frame.h lj_trace.h lj_jit.h lj_ir.h \
+ lj_dispatch.h lj_traceerr.h lj_vm.h lj_lex.h lj_parse.h
 lj_asm.o: lj_asm.c lj_obj.h lua.h luaconf.h lj_def.h lj_arch.h lj_gc.h \
  lj_str.h lj_tab.h lj_frame.h lj_bc.h lj_ctype.h lj_ir.h lj_jit.h \
  lj_ircall.h lj_iropt.h lj_mcode.h lj_trace.h lj_dispatch.h lj_traceerr.h \
@@ -83,11 +84,14 @@ lj_crecord.o: lj_crecord.c lj_obj.h lua.h luaconf.h lj_def.h lj_arch.h \
  lj_ffrecord.h lj_crecord.h
 lj_ctype.o: lj_ctype.c lj_obj.h lua.h luaconf.h lj_def.h lj_arch.h \
  lj_gc.h lj_err.h lj_errmsg.h lj_str.h lj_tab.h lj_ctype.h
+lj_debug.o: lj_debug.c lj_obj.h lua.h luaconf.h lj_def.h lj_arch.h \
+ lj_err.h lj_errmsg.h lj_str.h lj_tab.h lj_state.h lj_frame.h lj_bc.h
 lj_dispatch.o: lj_dispatch.c lj_obj.h lua.h luaconf.h lj_def.h lj_arch.h \
- lj_err.h lj_errmsg.h lj_state.h lj_frame.h lj_bc.h lj_ff.h lj_ffdef.h \
- lj_jit.h lj_ir.h lj_trace.h lj_dispatch.h lj_traceerr.h lj_vm.h luajit.h
+ lj_err.h lj_errmsg.h lj_debug.h lj_state.h lj_frame.h lj_bc.h lj_ff.h \
+ lj_ffdef.h lj_jit.h lj_ir.h lj_trace.h lj_dispatch.h lj_traceerr.h \
+ lj_vm.h luajit.h
 lj_err.o: lj_err.c lj_obj.h lua.h luaconf.h lj_def.h lj_arch.h lj_err.h \
- lj_errmsg.h lj_str.h lj_tab.h lj_func.h lj_state.h lj_frame.h lj_bc.h \
+ lj_errmsg.h lj_debug.h lj_str.h lj_func.h lj_state.h lj_frame.h lj_bc.h \
  lj_ff.h lj_ffdef.h lj_trace.h lj_jit.h lj_ir.h lj_dispatch.h \
  lj_traceerr.h lj_vm.h
 lj_ffrecord.o: lj_ffrecord.c lj_obj.h lua.h luaconf.h lj_def.h lj_arch.h \
@@ -103,8 +107,8 @@ lj_gc.o: lj_gc.c lj_obj.h lua.h luaconf.h lj_def.h lj_arch.h lj_gc.h \
  lj_state.h lj_frame.h lj_bc.h lj_ctype.h lj_cdata.h lj_trace.h lj_jit.h \
  lj_ir.h lj_dispatch.h lj_traceerr.h lj_vm.h
 lj_gdbjit.o: lj_gdbjit.c lj_obj.h lua.h luaconf.h lj_def.h lj_arch.h \
- lj_gc.h lj_err.h lj_errmsg.h lj_frame.h lj_bc.h lj_jit.h lj_ir.h \
- lj_dispatch.h
+ lj_gc.h lj_err.h lj_errmsg.h lj_debug.h lj_frame.h lj_bc.h lj_jit.h \
+ lj_ir.h lj_dispatch.h
 lj_ir.o: lj_ir.c lj_obj.h lua.h luaconf.h lj_def.h lj_arch.h lj_gc.h \
  lj_str.h lj_tab.h lj_ir.h lj_jit.h lj_ircall.h lj_iropt.h lj_trace.h \
  lj_dispatch.h lj_bc.h lj_traceerr.h lj_ctype.h lj_cdata.h lj_carith.h \
@@ -157,10 +161,10 @@ lj_str.o: lj_str.c lj_obj.h lua.h luaconf.h lj_def.h lj_arch.h lj_gc.h \
 lj_tab.o: lj_tab.c lj_obj.h lua.h luaconf.h lj_def.h lj_arch.h lj_gc.h \
  lj_err.h lj_errmsg.h lj_tab.h
 lj_trace.o: lj_trace.c lj_obj.h lua.h luaconf.h lj_def.h lj_arch.h \
- lj_gc.h lj_err.h lj_errmsg.h lj_str.h lj_frame.h lj_bc.h lj_state.h \
- lj_ir.h lj_jit.h lj_iropt.h lj_mcode.h lj_trace.h lj_dispatch.h \
- lj_traceerr.h lj_snap.h lj_gdbjit.h lj_record.h lj_asm.h lj_vm.h \
- lj_vmevent.h lj_target.h lj_target_*.h
+ lj_gc.h lj_err.h lj_errmsg.h lj_debug.h lj_str.h lj_frame.h lj_bc.h \
+ lj_state.h lj_ir.h lj_jit.h lj_iropt.h lj_mcode.h lj_trace.h \
+ lj_dispatch.h lj_traceerr.h lj_snap.h lj_gdbjit.h lj_record.h lj_asm.h \
+ lj_vm.h lj_vmevent.h lj_target.h lj_target_*.h
 lj_udata.o: lj_udata.c lj_obj.h lua.h luaconf.h lj_def.h lj_arch.h \
  lj_gc.h lj_udata.h
 lj_vmevent.o: lj_vmevent.c lj_obj.h lua.h luaconf.h lj_def.h lj_arch.h \
@@ -172,18 +176,19 @@ ljamalg.o: ljamalg.c lua.h luaconf.h lauxlib.h lj_gc.c lj_obj.h lj_def.h \
  lj_arch.h lj_gc.h lj_err.h lj_errmsg.h lj_str.h lj_tab.h lj_func.h \
  lj_udata.h lj_meta.h lj_state.h lj_frame.h lj_bc.h lj_ctype.h lj_cdata.h \
  lj_trace.h lj_jit.h lj_ir.h lj_dispatch.h lj_traceerr.h lj_vm.h lj_err.c \
- lj_ff.h lj_ffdef.h lj_char.c lj_char.h lj_bc.c lj_bcdef.h lj_obj.c \
- lj_str.c lj_tab.c lj_func.c lj_udata.c lj_meta.c lj_state.c lj_lex.h \
- lj_alloc.h lj_dispatch.c luajit.h lj_vmevent.c lj_vmevent.h lj_vmmath.c \
- lj_api.c lj_parse.h lj_lex.c lualib.h lj_parse.c lj_ctype.c lj_cdata.c \
- lj_cconv.h lj_cconv.c lj_ccall.c lj_ccall.h lj_carith.c lj_carith.h \
- lj_clib.c lj_clib.h lj_cparse.c lj_cparse.h lj_lib.c lj_lib.h lj_ir.c \
- lj_ircall.h lj_iropt.h lj_opt_mem.c lj_opt_fold.c lj_folddef.h \
- lj_opt_narrow.c lj_opt_dce.c lj_opt_loop.c lj_snap.h lj_opt_split.c \
- lj_mcode.c lj_mcode.h lj_snap.c lj_target.h lj_target_*.h lj_record.c \
- lj_record.h lj_ffrecord.h lj_crecord.c lj_crecord.h lj_ffrecord.c \
- lj_recdef.h lj_asm.c lj_asm.h lj_emit_*.h lj_asm_*.h lj_trace.c \
- lj_gdbjit.h lj_gdbjit.c lj_alloc.c lib_aux.c lib_base.c lj_libdef.h \
- lib_math.c lib_string.c lib_table.c lib_io.c lib_os.c lib_package.c \
- lib_debug.c lib_bit.c lib_jit.c lib_ffi.c lib_init.c
+ lj_debug.h lj_ff.h lj_ffdef.h lj_char.c lj_char.h lj_bc.c lj_bcdef.h \
+ lj_obj.c lj_str.c lj_tab.c lj_func.c lj_udata.c lj_meta.c lj_debug.c \
+ lj_state.c lj_lex.h lj_alloc.h lj_dispatch.c luajit.h lj_vmevent.c \
+ lj_vmevent.h lj_vmmath.c lj_api.c lj_parse.h lj_lex.c lualib.h \
+ lj_parse.c lj_ctype.c lj_cdata.c lj_cconv.h lj_cconv.c lj_ccall.c \
+ lj_ccall.h lj_carith.c lj_carith.h lj_clib.c lj_clib.h lj_cparse.c \
+ lj_cparse.h lj_lib.c lj_lib.h lj_ir.c lj_ircall.h lj_iropt.h \
+ lj_opt_mem.c lj_opt_fold.c lj_folddef.h lj_opt_narrow.c lj_opt_dce.c \
+ lj_opt_loop.c lj_snap.h lj_opt_split.c lj_mcode.c lj_mcode.h lj_snap.c \
+ lj_target.h lj_target_*.h lj_record.c lj_record.h lj_ffrecord.h \
+ lj_crecord.c lj_crecord.h lj_ffrecord.c lj_recdef.h lj_asm.c lj_asm.h \
+ lj_emit_*.h lj_asm_*.h lj_trace.c lj_gdbjit.h lj_gdbjit.c lj_alloc.c \
+ lib_aux.c lib_base.c lj_libdef.h lib_math.c lib_string.c lib_table.c \
+ lib_io.c lib_os.c lib_package.c lib_debug.c lib_bit.c lib_jit.c \
+ lib_ffi.c lib_init.c
 luajit.o: luajit.c lua.h luaconf.h lauxlib.h lualib.h luajit.h lj_arch.h
diff --git a/src/lib_base.c b/src/lib_base.c
index 8c71ae32..f8975986 100644
--- a/src/lib_base.c
+++ b/src/lib_base.c
@@ -18,6 +18,7 @@
 #include "lj_obj.h"
 #include "lj_gc.h"
 #include "lj_err.h"
+#include "lj_debug.h"
 #include "lj_str.h"
 #include "lj_tab.h"
 #include "lj_meta.h"
@@ -89,7 +90,7 @@ LJLIB_CF(getfenv)
   cTValue *o = L->base;
   if (!(o < L->top && tvisfunc(o))) {
     int level = lj_lib_optint(L, 1, 1);
-    o = lj_err_getframe(L, level, &level);
+    o = lj_debug_frame(L, level, &level);
     if (o == NULL)
       lj_err_arg(L, 1, LJ_ERR_INVLVL);
   }
@@ -110,7 +111,7 @@ LJLIB_CF(setfenv)
       setgcref(L->env, obj2gco(t));
       return 0;
     }
-    o = lj_err_getframe(L, level, &level);
+    o = lj_debug_frame(L, level, &level);
     if (o == NULL)
       lj_err_arg(L, 1, LJ_ERR_INVLVL);
   }
diff --git a/src/lib_jit.c b/src/lib_jit.c
index 6e16d45b..758835aa 100644
--- a/src/lib_jit.c
+++ b/src/lib_jit.c
@@ -13,6 +13,7 @@
 #include "lj_arch.h"
 #include "lj_obj.h"
 #include "lj_err.h"
+#include "lj_debug.h"
 #include "lj_str.h"
 #include "lj_tab.h"
 #include "lj_bc.h"
@@ -189,13 +190,12 @@ LJLIB_CF(jit_util_funcinfo)
     setintfield(L, t, "nconsts", (int32_t)pt->sizekn);
     setintfield(L, t, "upvalues", (int32_t)pt->sizeuv);
     if (pc < pt->sizebc)
-      setintfield(L, t, "currentline",
-		  proto_lineinfo(pt) ? proto_line(pt, pc) : 0);
+      setintfield(L, t, "currentline", lj_debug_line(pt, pc));
     lua_pushboolean(L, (pt->flags & PROTO_IS_VARARG));
     lua_setfield(L, -2, "isvararg");
     setstrV(L, L->top++, proto_chunkname(pt));
     lua_setfield(L, -2, "source");
-    lj_err_pushloc(L, pt, pc);
+    lj_debug_pushloc(L, pt, pc);
     lua_setfield(L, -2, "loc");
   } else {
     GCfunc *fn = funcV(L->base);
diff --git a/src/lj_api.c b/src/lj_api.c
index 3a8448b5..4e41ccc0 100644
--- a/src/lj_api.c
+++ b/src/lj_api.c
@@ -12,6 +12,7 @@
 #include "lj_obj.h"
 #include "lj_gc.h"
 #include "lj_err.h"
+#include "lj_debug.h"
 #include "lj_str.h"
 #include "lj_tab.h"
 #include "lj_func.h"
@@ -27,7 +28,7 @@
 
 /* -- Common helper functions --------------------------------------------- */
 
-#define api_checknelems(L, n)	api_check(L, (n) <= (L->top - L->base))
+#define api_checknelems(L, n)		api_check(L, (n) <= (L->top - L->base))
 #define api_checkvalidindex(L, i)	api_check(L, (i) != niltv(L))
 
 static TValue *index2adr(lua_State *L, int idx)
@@ -832,30 +833,10 @@ LUA_API int lua_next(lua_State *L, int idx)
   return more;
 }
 
-static const char *aux_upvalue(cTValue *f, uint32_t idx, TValue **val)
-{
-  GCfunc *fn;
-  if (!tvisfunc(f)) return NULL;
-  fn = funcV(f);
-  if (isluafunc(fn)) {
-    GCproto *pt = funcproto(fn);
-    if (idx < pt->sizeuv) {
-      *val = uvval(&gcref(fn->l.uvptr[idx])->uv);
-      return strdata(proto_uvname(pt, idx));
-    }
-  } else {
-    if (idx < fn->c.nupvalues) {
-      *val = &fn->c.upvalue[idx];
-      return "";
-    }
-  }
-  return NULL;
-}
-
 LUA_API const char *lua_getupvalue(lua_State *L, int idx, int n)
 {
   TValue *val;
-  const char *name = aux_upvalue(index2adr(L, idx), (uint32_t)(n-1), &val);
+  const char *name = lj_debug_uvname(index2adr(L, idx), (uint32_t)(n-1), &val);
   if (name) {
     copyTV(L, L->top, val);
     incr_top(L);
@@ -1010,7 +991,7 @@ LUA_API const char *lua_setupvalue(lua_State *L, int idx, int n)
   TValue *val;
   const char *name;
   api_checknelems(L, 1);
-  name = aux_upvalue(f, (uint32_t)(n-1), &val);
+  name = lj_debug_uvname(f, (uint32_t)(n-1), &val);
   if (name) {
     L->top--;
     copyTV(L, val, L->top);
diff --git a/src/lj_debug.c b/src/lj_debug.c
new file mode 100644
index 00000000..a5ffff74
--- /dev/null
+++ b/src/lj_debug.c
@@ -0,0 +1,429 @@
+/*
+** Debugging and introspection.
+** Copyright (C) 2005-2011 Mike Pall. See Copyright Notice in luajit.h
+*/
+
+#define lj_debug_c
+#define LUA_CORE
+
+#include "lj_obj.h"
+#include "lj_err.h"
+#include "lj_str.h"
+#include "lj_tab.h"
+#include "lj_state.h"
+#include "lj_frame.h"
+#include "lj_bc.h"
+
+/* -- Frames -------------------------------------------------------------- */
+
+/* Get frame corresponding to a level. */
+cTValue *lj_debug_frame(lua_State *L, int level, int *size)
+{
+  cTValue *frame, *nextframe, *bot = tvref(L->stack);
+  /* Traverse frames backwards. */
+  for (nextframe = frame = L->base-1; frame > bot; ) {
+    if (frame_gc(frame) == obj2gco(L))
+      level++;  /* Skip dummy frames. See lj_meta_call(). */
+    if (level-- == 0) {
+      *size = (int)(nextframe - frame);
+      return frame;  /* Level found. */
+    }
+    nextframe = frame;
+    if (frame_islua(frame)) {
+      frame = frame_prevl(frame);
+    } else {
+      if (frame_isvarg(frame))
+	level++;  /* Skip vararg pseudo-frame. */
+      frame = frame_prevd(frame);
+    }
+  }
+  *size = level;
+  return NULL;  /* Level not found. */
+}
+
+/* Invalid bytecode position. */
+#define NO_BCPOS	(~(BCPos)0)
+
+/* Return bytecode position for function/frame or NO_BCPOS. */
+static BCPos debug_framepc(lua_State *L, GCfunc *fn, cTValue *nextframe)
+{
+  const BCIns *ins;
+  lua_assert(fn->c.gct == ~LJ_TFUNC || fn->c.gct == ~LJ_TTHREAD);
+  if (!isluafunc(fn)) {  /* Cannot derive a PC for non-Lua functions. */
+    return NO_BCPOS;
+  } else if (nextframe == NULL) {  /* Lua function on top. */
+    void *cf = cframe_raw(L->cframe);
+    if (cf == NULL || (char *)cframe_pc(cf) == (char *)cframe_L(cf))
+      return NO_BCPOS;
+    ins = cframe_pc(cf);  /* Only happens during error/hook handling. */
+  } else {
+    if (frame_islua(nextframe)) {
+      ins = frame_pc(nextframe);
+    } else if (frame_iscont(nextframe)) {
+      ins = frame_contpc(nextframe);
+    } else {
+      /* Lua function below errfunc/gc/hook: find cframe to get the PC. */
+      void *cf = cframe_raw(L->cframe);
+      TValue *f = L->base-1;
+      if (cf == NULL)
+	return NO_BCPOS;
+      while (f > nextframe) {
+	if (frame_islua(f)) {
+	  f = frame_prevl(f);
+	} else {
+	  if (frame_isc(f))
+	    cf = cframe_raw(cframe_prev(cf));
+	  f = frame_prevd(f);
+	}
+      }
+      if (cframe_prev(cf))
+	cf = cframe_raw(cframe_prev(cf));
+      ins = cframe_pc(cf);
+    }
+  }
+  return proto_bcpos(funcproto(fn), ins) - 1;
+}
+
+/* -- Line numbers -------------------------------------------------------- */
+
+/* Get line number for a bytecode position. */
+BCLine LJ_FASTCALL lj_debug_line(GCproto *pt, BCPos pc)
+{
+  BCLine *lineinfo = proto_lineinfo(pt);
+  if (pc < pt->sizebc && lineinfo)
+    return lineinfo[pc];
+  return 0;
+}
+
+/* Get line number for function/frame. */
+static BCLine debug_frameline(lua_State *L, GCfunc *fn, cTValue *nextframe)
+{
+  BCPos pc = debug_framepc(L, fn, nextframe);
+  if (pc != NO_BCPOS) {
+    GCproto *pt = funcproto(fn);
+    lua_assert(pc < pt->sizebc);
+    return lj_debug_line(pt, pc);
+  }
+  return -1;
+}
+
+/* -- Variable names ------------------------------------------------------ */
+
+/* Get name of a local variable from slot number and PC. */
+static const char *debug_varname(const GCproto *pt, BCPos pc, BCReg slot)
+{
+  MSize i;
+  VarInfo *vi = proto_varinfo(pt);
+  for (i = 0; i < pt->sizevarinfo && vi[i].startpc <= pc; i++)
+    if (pc < vi[i].endpc && slot-- == 0)
+      return strdata(gco2str(gcref(vi[i].name)));
+  return NULL;
+}
+
+/* Get name of local variable from 1-based slot number and function/frame. */
+static TValue *debug_localname(lua_State *L, const lua_Debug *ar,
+			       const char **name, BCReg slot1)
+{
+  uint32_t offset = (uint32_t)ar->i_ci & 0xffff;
+  uint32_t size = (uint32_t)ar->i_ci >> 16;
+  TValue *frame = tvref(L->stack) + offset;
+  TValue *nextframe = size ? frame + size : NULL;
+  GCfunc *fn = frame_func(frame);
+  BCPos pc = debug_framepc(L, fn, nextframe);
+  if (pc != NO_BCPOS &&
+      (*name = debug_varname(funcproto(fn), pc, slot1-1)) != NULL)
+    ;
+  else if (slot1 > 0 && frame + slot1 < (nextframe ? nextframe : L->top))
+    *name = "(*temporary)";
+  else
+    *name = NULL;
+  return frame+slot1;
+}
+
+/* Get name of upvalue. */
+const char *lj_debug_uvname(cTValue *o, uint32_t idx, TValue **tvp)
+{
+  if (tvisfunc(o)) {
+    GCfunc *fn = funcV(o);
+    if (isluafunc(fn)) {
+      GCproto *pt = funcproto(fn);
+      if (idx < pt->sizeuv) {
+	*tvp = uvval(&gcref(fn->l.uvptr[idx])->uv);
+	return strdata(proto_uvname(pt, idx));
+      }
+    } else {
+      if (idx < fn->c.nupvalues) {
+	*tvp = &fn->c.upvalue[idx];
+	return "";
+      }
+    }
+  }
+  return NULL;
+}
+
+/* Deduce name of an object from slot number and PC. */
+const char *lj_debug_slotname(GCproto *pt, const BCIns *ip, BCReg slot,
+			      const char **name)
+{
+  const char *lname;
+restart:
+  lname = debug_varname(pt, proto_bcpos(pt, ip), slot);
+  if (lname != NULL) { *name = lname; return "local"; }
+  while (--ip > proto_bc(pt)) {
+    BCIns ins = *ip;
+    BCOp op = bc_op(ins);
+    BCReg ra = bc_a(ins);
+    if (bcmode_a(op) == BCMbase) {
+      if (slot >= ra && (op != BC_KNIL || slot <= bc_d(ins)))
+	return NULL;
+    } else if (bcmode_a(op) == BCMdst && ra == slot) {
+      switch (bc_op(ins)) {
+      case BC_MOV:
+	if (ra == slot) { slot = bc_d(ins); goto restart; }
+	break;
+      case BC_GGET:
+	*name = strdata(gco2str(proto_kgc(pt, ~(ptrdiff_t)bc_d(ins))));
+	return "global";
+      case BC_TGETS:
+	*name = strdata(gco2str(proto_kgc(pt, ~(ptrdiff_t)bc_c(ins))));
+	if (ip > proto_bc(pt)) {
+	  BCIns insp = ip[-1];
+	  if (bc_op(insp) == BC_MOV && bc_a(insp) == ra+1 &&
+	      bc_d(insp) == bc_b(ins))
+	    return "method";
+	}
+	return "field";
+      case BC_UGET:
+	*name = strdata(proto_uvname(pt, bc_d(ins)));
+	return "upvalue";
+      default:
+	return NULL;
+      }
+    }
+  }
+  return NULL;
+}
+
+/* Deduce function name from caller of a frame. */
+const char *lj_debug_funcname(lua_State *L, TValue *frame, const char **name)
+{
+  TValue *pframe;
+  GCfunc *fn;
+  BCPos pc;
+  if (frame_isvarg(frame))
+    frame = frame_prevd(frame);
+  pframe = frame_prev(frame);
+  fn = frame_func(pframe);
+  pc = debug_framepc(L, fn, frame);
+  if (pc != NO_BCPOS) {
+    GCproto *pt = funcproto(fn);
+    const BCIns *ip = &proto_bc(pt)[check_exp(pc < pt->sizebc, pc)];
+    MMS mm = bcmode_mm(bc_op(*ip));
+    if (mm == MM_call) {
+      BCReg slot = bc_a(*ip);
+      if (bc_op(*ip) == BC_ITERC) slot -= 3;
+      return lj_debug_slotname(pt, ip, slot, name);
+    } else if (mm != MM__MAX) {
+      *name = strdata(mmname_str(G(L), mm));
+      return "metamethod";
+    }
+  }
+  return NULL;
+}
+
+/* -- Source code locations ----------------------------------------------- */
+
+/* Generate shortened source name. */
+void lj_debug_shortname(char *out, const char *src)
+{
+  if (*src == '=') {
+    strncpy(out, src+1, LUA_IDSIZE);  /* remove first char */
+    out[LUA_IDSIZE-1] = '\0';  /* ensures null termination */
+  } else if (*src == '@') { /* out = "source", or "...source" */
+    size_t l = strlen(++src);  /* skip the `@' */
+    if (l >= LUA_IDSIZE) {
+      src += l-(LUA_IDSIZE-4);  /* get last part of file name */
+      strcpy(out, "...");
+      out += 3;
+    }
+    strcpy(out, src);
+  } else {  /* out = [string "string"] */
+    size_t len; /* Length, up to first control char. */
+    for (len = 0; len < LUA_IDSIZE-12; len++)
+      if (((const unsigned char *)src)[len] < ' ') break;
+    strcpy(out, "[string \""); out += 9;
+    if (src[len] != '\0') {  /* must truncate? */
+      if (len > LUA_IDSIZE-15) len = LUA_IDSIZE-15;
+      strncpy(out, src, len); out += len;
+      strcpy(out, "..."); out += 3;
+    } else {
+      strcpy(out, src); out += len;
+    }
+    strcpy(out, "\"]");
+  }
+}
+
+/* Add current location of a frame to error message. */
+void lj_debug_addloc(lua_State *L, const char *msg,
+		     cTValue *frame, cTValue *nextframe)
+{
+  if (frame) {
+    GCfunc *fn = frame_func(frame);
+    if (isluafunc(fn)) {
+      BCLine line = debug_frameline(L, fn, nextframe);
+      if (line >= 0) {
+	char buf[LUA_IDSIZE];
+	lj_debug_shortname(buf, strdata(proto_chunkname(funcproto(fn))));
+	lj_str_pushf(L, "%s:%d: %s", buf, line, msg);
+	return;
+      }
+    }
+  }
+  lj_str_pushf(L, "%s", msg);
+}
+
+/* Push location string for a bytecode position to Lua stack. */
+void lj_debug_pushloc(lua_State *L, GCproto *pt, BCPos pc)
+{
+  GCstr *name = proto_chunkname(pt);
+  if (name) {
+    const char *s = strdata(name);
+    MSize i, len = name->len;
+    BCLine line = lj_debug_line(pt, pc);
+    if (*s == '@') {
+      s++; len--;
+      for (i = len; i > 0; i--)
+	if (s[i] == '/' || s[i] == '\\') {
+	  s += i+1;
+	  break;
+	}
+      lj_str_pushf(L, "%s:%d", s, line);
+    } else if (len > 40) {
+      lj_str_pushf(L, "%p:%d", pt, line);
+    } else if (*s == '=') {
+      lj_str_pushf(L, "%s:%d", s+1, line);
+    } else {
+      lj_str_pushf(L, "\"%s\":%d", s, line);
+    }
+  } else {
+    lj_str_pushf(L, "%p:%u", pt, pc);
+  }
+}
+
+/* -- Public debug API ---------------------------------------------------- */
+
+/* lua_getupvalue() and lua_setupvalue() are in lj_api.c. */
+
+LUA_API const char *lua_getlocal(lua_State *L, const lua_Debug *ar, int n)
+{
+  const char *name;
+  TValue *o = debug_localname(L, ar, &name, (BCReg)n);
+  if (name) {
+    copyTV(L, L->top, o);
+    incr_top(L);
+  }
+  return name;
+}
+
+LUA_API const char *lua_setlocal(lua_State *L, const lua_Debug *ar, int n)
+{
+  const char *name;
+  TValue *o = debug_localname(L, ar, &name, (BCReg)n);
+  if (name)
+    copyTV(L, o, L->top-1);
+  L->top--;
+  return name;
+}
+
+LUA_API int lua_getinfo(lua_State *L, const char *what, lua_Debug *ar)
+{
+  int status = 1;
+  TValue *frame = NULL;
+  TValue *nextframe = NULL;
+  GCfunc *fn;
+  if (*what == '>') {
+    TValue *func = L->top - 1;
+    api_check(L, tvisfunc(func));
+    fn = funcV(func);
+    L->top--;
+    what++;
+  } else {
+    uint32_t offset = (uint32_t)ar->i_ci & 0xffff;
+    uint32_t size = (uint32_t)ar->i_ci >> 16;
+    lua_assert(offset != 0);
+    frame = tvref(L->stack) + offset;
+    if (size) nextframe = frame + size;
+    lua_assert(frame <= tvref(L->maxstack) &&
+	       (!nextframe || nextframe <= tvref(L->maxstack)));
+    fn = frame_func(frame);
+    lua_assert(fn->c.gct == ~LJ_TFUNC);
+  }
+  for (; *what; what++) {
+    switch (*what) {
+    case 'S':
+      if (isluafunc(fn)) {
+	GCproto *pt = funcproto(fn);
+	ar->source = strdata(proto_chunkname(pt));
+	ar->linedefined = (int)proto_line(pt, 0);
+	ar->lastlinedefined = (int)pt->lastlinedefined;
+	ar->what = ar->linedefined ? "Lua" : "main";
+      } else {
+	ar->source = "=[C]";
+	ar->linedefined = -1;
+	ar->lastlinedefined = -1;
+	ar->what = "C";
+      }
+      lj_debug_shortname(ar->short_src, ar->source);
+      break;
+    case 'l':
+      ar->currentline = frame ? debug_frameline(L, fn, nextframe) : -1;
+      break;
+    case 'u':
+      ar->nups = fn->c.nupvalues;
+      break;
+    case 'n':
+      ar->namewhat = frame ? lj_debug_funcname(L, frame, &ar->name) : NULL;
+      if (ar->namewhat == NULL) {
+	ar->namewhat = "";
+	ar->name = NULL;
+      }
+      break;
+    case 'f':
+      setfuncV(L, L->top, fn);
+      incr_top(L);
+      break;
+    case 'L':
+      if (isluafunc(fn)) {
+	GCtab *t = lj_tab_new(L, 0, 0);
+	GCproto *pt = funcproto(fn);
+	BCLine *lineinfo = proto_lineinfo(pt);
+	MSize i, szl = pt->sizebc;
+	for (i = 1; i < szl; i++)
+	  setboolV(lj_tab_setint(L, t, lineinfo[i]), 1);
+	settabV(L, L->top, t);
+      } else {
+	setnilV(L->top);
+      }
+      incr_top(L);
+      break;
+    default:
+      status = 0;  /* Bad option. */
+      break;
+    }
+  }
+  return status;
+}
+
+LUA_API int lua_getstack(lua_State *L, int level, lua_Debug *ar)
+{
+  int size;
+  cTValue *frame = lj_debug_frame(L, level, &size);
+  if (frame) {
+    ar->i_ci = (size << 16) + (int)(frame - tvref(L->stack));
+    return 1;
+  } else {
+    ar->i_ci = level - size;
+    return 0;
+  }
+}
+
diff --git a/src/lj_debug.h b/src/lj_debug.h
new file mode 100644
index 00000000..5a1ddbec
--- /dev/null
+++ b/src/lj_debug.h
@@ -0,0 +1,23 @@
+/*
+** Debugging and introspection.
+** Copyright (C) 2005-2011 Mike Pall. See Copyright Notice in luajit.h
+*/
+
+#ifndef _LJ_DEBUG_H
+#define _LJ_DEBUG_H
+
+#include "lj_obj.h"
+
+LJ_FUNC cTValue *lj_debug_frame(lua_State *L, int level, int *size);
+LJ_FUNC BCLine LJ_FASTCALL lj_debug_line(GCproto *pt, BCPos pc);
+LJ_FUNC const char *lj_debug_uvname(cTValue *o, uint32_t idx, TValue **tvp);
+LJ_FUNC const char *lj_debug_slotname(GCproto *pt, const BCIns *pc,
+				      BCReg slot, const char **name);
+LJ_FUNC const char *lj_debug_funcname(lua_State *L, TValue *frame,
+				      const char **name);
+LJ_FUNC void lj_debug_shortname(char *out, const char *src);
+LJ_FUNC void lj_debug_addloc(lua_State *L, const char *msg,
+			     cTValue *frame, cTValue *nextframe);
+LJ_FUNC void lj_debug_pushloc(lua_State *L, GCproto *pt, BCPos pc);
+
+#endif
diff --git a/src/lj_dispatch.c b/src/lj_dispatch.c
index 425eeaa2..5fbc112c 100644
--- a/src/lj_dispatch.c
+++ b/src/lj_dispatch.c
@@ -8,6 +8,7 @@
 
 #include "lj_obj.h"
 #include "lj_err.h"
+#include "lj_debug.h"
 #include "lj_state.h"
 #include "lj_frame.h"
 #include "lj_bc.h"
@@ -380,8 +381,8 @@ void LJ_FASTCALL lj_dispatch_ins(lua_State *L, const BCIns *pc)
   if ((g->hookmask & LUA_MASKLINE)) {
     BCPos npc = proto_bcpos(pt, pc) - 1;
     BCPos opc = proto_bcpos(pt, oldpc) - 1;
-    BCLine line = proto_line(pt, npc);
-    if (pc <= oldpc || opc >= pt->sizebc || line != proto_line(pt, opc)) {
+    BCLine line = lj_debug_line(pt, npc);
+    if (pc <= oldpc || opc >= pt->sizebc || line != lj_debug_line(pt, opc)) {
       callhook(L, LUA_HOOKLINE, line);
       L->top = L->base + slots;  /* Fix top again. */
     }
diff --git a/src/lj_err.c b/src/lj_err.c
index 61178805..8d37af6a 100644
--- a/src/lj_err.c
+++ b/src/lj_err.c
@@ -1,9 +1,6 @@
 /*
-** Error handling and debugging API.
+** Error handling.
 ** Copyright (C) 2005-2011 Mike Pall. See Copyright Notice in luajit.h
-**
-** Portions taken verbatim or adapted from the Lua interpreter.
-** Copyright (C) 1994-2008 Lua.org, PUC-Rio. See Copyright Notice in lua.h
 */
 
 #define lj_err_c
@@ -11,12 +8,11 @@
 
 #include "lj_obj.h"
 #include "lj_err.h"
+#include "lj_debug.h"
 #include "lj_str.h"
-#include "lj_tab.h"
 #include "lj_func.h"
 #include "lj_state.h"
 #include "lj_frame.h"
-#include "lj_bc.h"
 #include "lj_ff.h"
 #include "lj_trace.h"
 #include "lj_vm.h"
@@ -78,355 +74,6 @@ LJ_DATADEF const char *lj_err_allmsg =
 #include "lj_errmsg.h"
 ;
 
-/* -- Frame and function introspection ------------------------------------ */
-
-static BCPos currentpc(lua_State *L, GCfunc *fn, cTValue *nextframe)
-{
-  const BCIns *ins;
-  lua_assert(fn->c.gct == ~LJ_TFUNC || fn->c.gct == ~LJ_TTHREAD);
-  if (!isluafunc(fn)) {  /* Cannot derive a PC for non-Lua functions. */
-    return ~(BCPos)0;
-  } else if (nextframe == NULL) {  /* Lua function on top. */
-    void *cf = cframe_raw(L->cframe);
-    if (cf == NULL || (char *)cframe_pc(cf) == (char *)cframe_L(cf))
-      return ~(BCPos)0;
-    ins = cframe_pc(cf);  /* Only happens during error/hook handling. */
-  } else {
-    if (frame_islua(nextframe)) {
-      ins = frame_pc(nextframe);
-    } else if (frame_iscont(nextframe)) {
-      ins = frame_contpc(nextframe);
-    } else {
-      /* Lua function below errfunc/gc/hook: find cframe to get the PC. */
-      void *cf = cframe_raw(L->cframe);
-      TValue *f = L->base-1;
-      if (cf == NULL)
-	return ~(BCPos)0;
-      while (f > nextframe) {
-	if (frame_islua(f)) {
-	  f = frame_prevl(f);
-	} else {
-	  if (frame_isc(f))
-	    cf = cframe_raw(cframe_prev(cf));
-	  f = frame_prevd(f);
-	}
-      }
-      if (cframe_prev(cf))
-	cf = cframe_raw(cframe_prev(cf));
-      ins = cframe_pc(cf);
-    }
-  }
-  return proto_bcpos(funcproto(fn), ins) - 1;
-}
-
-static BCLine currentline(lua_State *L, GCfunc *fn, cTValue *nextframe)
-{
-  BCPos pc = currentpc(L, fn, nextframe);
-  if (pc != ~(BCPos)0) {
-    GCproto *pt = funcproto(fn);
-    lua_assert(pc < pt->sizebc);
-    return proto_line(pt, pc);
-  } else {
-    return -1;
-  }
-}
-
-static const char *getvarname(const GCproto *pt, BCPos pc, BCReg slot)
-{
-  MSize i;
-  VarInfo *vi = proto_varinfo(pt);
-  for (i = 0; i < pt->sizevarinfo && vi[i].startpc <= pc; i++)
-    if (pc < vi[i].endpc && slot-- == 0)
-      return strdata(gco2str(gcref(vi[i].name)));
-  return NULL;
-}
-
-static const char *getobjname(GCproto *pt, const BCIns *ip, BCReg slot,
-			      const char **name)
-{
-  const char *lname;
-restart:
-  lname = getvarname(pt, proto_bcpos(pt, ip), slot);
-  if (lname != NULL) { *name = lname; return "local"; }
-  while (--ip > proto_bc(pt)) {
-    BCIns ins = *ip;
-    BCOp op = bc_op(ins);
-    BCReg ra = bc_a(ins);
-    if (bcmode_a(op) == BCMbase) {
-      if (slot >= ra && (op != BC_KNIL || slot <= bc_d(ins)))
-	return NULL;
-    } else if (bcmode_a(op) == BCMdst && ra == slot) {
-      switch (bc_op(ins)) {
-      case BC_MOV:
-	if (ra == slot) { slot = bc_d(ins); goto restart; }
-	break;
-      case BC_GGET:
-	*name = strdata(gco2str(proto_kgc(pt, ~(ptrdiff_t)bc_d(ins))));
-	return "global";
-      case BC_TGETS:
-	*name = strdata(gco2str(proto_kgc(pt, ~(ptrdiff_t)bc_c(ins))));
-	if (ip > proto_bc(pt)) {
-	  BCIns insp = ip[-1];
-	  if (bc_op(insp) == BC_MOV && bc_a(insp) == ra+1 &&
-	      bc_d(insp) == bc_b(ins))
-	    return "method";
-	}
-	return "field";
-      case BC_UGET:
-	*name = strdata(proto_uvname(pt, bc_d(ins)));
-	return "upvalue";
-      default:
-	return NULL;
-      }
-    }
-  }
-  return NULL;
-}
-
-static const char *getfuncname(lua_State *L, TValue *frame, const char **name)
-{
-  MMS mm;
-  const BCIns *ip;
-  TValue *pframe;
-  GCfunc *fn;
-  BCPos pc;
-  if (frame_isvarg(frame))
-    frame = frame_prevd(frame);
-  pframe = frame_prev(frame);
-  fn = frame_func(pframe);
-  pc = currentpc(L, fn, frame);
-  if (pc == ~(BCPos)0)
-    return NULL;
-  lua_assert(pc < funcproto(fn)->sizebc);
-  ip = &proto_bc(funcproto(fn))[pc];
-  mm = bcmode_mm(bc_op(*ip));
-  if (mm == MM_call) {
-    BCReg slot = bc_a(*ip);
-    if (bc_op(*ip) == BC_ITERC) slot -= 3;
-    return getobjname(funcproto(fn), ip, slot, name);
-  } else if (mm != MM__MAX) {
-    *name = strdata(mmname_str(G(L), mm));
-    return "metamethod";
-  } else {
-    return NULL;
-  }
-}
-
-void lj_err_pushloc(lua_State *L, GCproto *pt, BCPos pc)
-{
-  GCstr *name = proto_chunkname(pt);
-  if (name) {
-    const char *s = strdata(name);
-    MSize i, len = name->len;
-    BCLine line = pc < pt->sizebc ? proto_line(pt, pc) : 0;
-    if (*s == '@') {
-      s++; len--;
-      for (i = len; i > 0; i--)
-	if (s[i] == '/' || s[i] == '\\') {
-	  s += i+1;
-	  break;
-	}
-      lj_str_pushf(L, "%s:%d", s, line);
-    } else if (len > 40) {
-      lj_str_pushf(L, "%p:%d", pt, line);
-    } else if (*s == '=') {
-      lj_str_pushf(L, "%s:%d", s+1, line);
-    } else {
-      lj_str_pushf(L, "\"%s\":%d", s, line);
-    }
-  } else {
-    lj_str_pushf(L, "%p:%u", pt, pc);
-  }
-}
-
-static void err_chunkid(char *out, const char *src)
-{
-  if (*src == '=') {
-    strncpy(out, src+1, LUA_IDSIZE);  /* remove first char */
-    out[LUA_IDSIZE-1] = '\0';  /* ensures null termination */
-  } else if (*src == '@') { /* out = "source", or "...source" */
-    size_t l = strlen(++src);  /* skip the `@' */
-    if (l >= LUA_IDSIZE) {
-      src += l-(LUA_IDSIZE-4);  /* get last part of file name */
-      strcpy(out, "...");
-      out += 3;
-    }
-    strcpy(out, src);
-  } else {  /* out = [string "string"] */
-    size_t len; /* Length, up to first control char. */
-    for (len = 0; len < LUA_IDSIZE-12; len++)
-      if (((const unsigned char *)src)[len] < ' ') break;
-    strcpy(out, "[string \""); out += 9;
-    if (src[len] != '\0') {  /* must truncate? */
-      if (len > LUA_IDSIZE-15) len = LUA_IDSIZE-15;
-      strncpy(out, src, len); out += len;
-      strcpy(out, "..."); out += 3;
-    } else {
-      strcpy(out, src); out += len;
-    }
-    strcpy(out, "\"]");
-  }
-}
-
-/* -- Public debug API ---------------------------------------------------- */
-
-static TValue *findlocal(lua_State *L, const lua_Debug *ar,
-			 const char **name, BCReg slot)
-{
-  uint32_t offset = (uint32_t)ar->i_ci & 0xffff;
-  uint32_t size = (uint32_t)ar->i_ci >> 16;
-  TValue *frame = tvref(L->stack) + offset;
-  TValue *nextframe = size ? frame + size : NULL;
-  GCfunc *fn = frame_func(frame);
-  BCPos pc = currentpc(L, fn, nextframe);
-  if (pc != ~(BCPos)0 &&
-      (*name = getvarname(funcproto(fn), pc, slot-1)) != NULL)
-    ;
-  else if (slot > 0 && frame + slot < (nextframe ? nextframe : L->top))
-    *name = "(*temporary)";
-  else
-    *name = NULL;
-  return frame+slot;
-}
-
-LUA_API const char *lua_getlocal(lua_State *L, const lua_Debug *ar, int n)
-{
-  const char *name;
-  TValue *o = findlocal(L, ar, &name, (BCReg)n);
-  if (name) {
-    copyTV(L, L->top, o);
-    incr_top(L);
-  }
-  return name;
-}
-
-
-LUA_API const char *lua_setlocal(lua_State *L, const lua_Debug *ar, int n)
-{
-  const char *name;
-  TValue *o = findlocal(L, ar, &name, (BCReg)n);
-  if (name)
-    copyTV(L, o, L->top-1);
-  L->top--;
-  return name;
-}
-
-LUA_API int lua_getinfo(lua_State *L, const char *what, lua_Debug *ar)
-{
-  int status = 1;
-  TValue *frame = NULL;
-  TValue *nextframe = NULL;
-  GCfunc *fn;
-  if (*what == '>') {
-    TValue *func = L->top - 1;
-    api_check(L, tvisfunc(func));
-    fn = funcV(func);
-    L->top--;
-    what++;
-  } else {
-    uint32_t offset = (uint32_t)ar->i_ci & 0xffff;
-    uint32_t size = (uint32_t)ar->i_ci >> 16;
-    lua_assert(offset != 0);
-    frame = tvref(L->stack) + offset;
-    if (size) nextframe = frame + size;
-    lua_assert(frame <= tvref(L->maxstack) &&
-	       (!nextframe || nextframe <= tvref(L->maxstack)));
-    fn = frame_func(frame);
-    lua_assert(fn->c.gct == ~LJ_TFUNC);
-  }
-  for (; *what; what++) {
-    switch (*what) {
-    case 'S':
-      if (isluafunc(fn)) {
-	GCproto *pt = funcproto(fn);
-	ar->source = strdata(proto_chunkname(pt));
-	ar->linedefined = (int)proto_line(pt, 0);
-	ar->lastlinedefined = (int)pt->lastlinedefined;
-	ar->what = (ar->linedefined == 0) ? "main" : "Lua";
-      } else {
-	ar->source = "=[C]";
-	ar->linedefined = -1;
-	ar->lastlinedefined = -1;
-	ar->what = "C";
-      }
-      err_chunkid(ar->short_src, ar->source);
-      break;
-    case 'l':
-      ar->currentline = frame ? currentline(L, fn, nextframe) : -1;
-      break;
-    case 'u':
-      ar->nups = fn->c.nupvalues;
-      break;
-    case 'n':
-      ar->namewhat = frame ? getfuncname(L, frame, &ar->name) : NULL;
-      if (ar->namewhat == NULL) {
-	ar->namewhat = "";
-	ar->name = NULL;
-      }
-      break;
-    case 'f':
-      setfuncV(L, L->top, fn);
-      incr_top(L);
-      break;
-    case 'L':
-      if (isluafunc(fn)) {
-	GCtab *t = lj_tab_new(L, 0, 0);
-	GCproto *pt = funcproto(fn);
-	BCLine *lineinfo = proto_lineinfo(pt);
-	MSize i, szl = pt->sizebc;
-	for (i = 1; i < szl; i++)
-	  setboolV(lj_tab_setint(L, t, lineinfo[i]), 1);
-	settabV(L, L->top, t);
-      } else {
-	setnilV(L->top);
-      }
-      incr_top(L);
-      break;
-    default:
-      status = 0;  /* Bad option. */
-      break;
-    }
-  }
-  return status;
-}
-
-cTValue *lj_err_getframe(lua_State *L, int level, int *size)
-{
-  cTValue *frame, *nextframe, *bot = tvref(L->stack);
-  /* Traverse frames backwards. */
-  for (nextframe = frame = L->base-1; frame > bot; ) {
-    if (frame_gc(frame) == obj2gco(L))
-      level++;  /* Skip dummy frames. See lj_meta_call(). */
-    if (level-- == 0) {
-      *size = (int)(nextframe - frame);
-      return frame;  /* Level found. */
-    }
-    nextframe = frame;
-    if (frame_islua(frame)) {
-      frame = frame_prevl(frame);
-    } else {
-      if (frame_isvarg(frame))
-	level++;  /* Skip vararg pseudo-frame. */
-      frame = frame_prevd(frame);
-    }
-  }
-  *size = level;
-  return NULL;  /* Level not found. */
-}
-
-LUA_API int lua_getstack(lua_State *L, int level, lua_Debug *ar)
-{
-  int size;
-  cTValue *frame = lj_err_getframe(L, level, &size);
-  if (frame) {
-    ar->i_ci = (size << 16) + (int)(frame - tvref(L->stack));
-    return 1;
-  } else {
-    ar->i_ci = level - size;
-    return 0;
-  }
-}
-
 /* -- Internal frame unwinding -------------------------------------------- */
 
 /* Unwind Lua stack and move error message to new top. */
@@ -854,25 +501,6 @@ LJ_NOINLINE void lj_err_run(lua_State *L)
   lj_err_throw(L, LUA_ERRRUN);
 }
 
-/* Add location to error message. */
-LJ_NOINLINE static void err_loc(lua_State *L, const char *msg,
-				cTValue *frame, cTValue *nextframe)
-{
-  if (frame) {
-    GCfunc *fn = frame_func(frame);
-    if (isluafunc(fn)) {
-      char buff[LUA_IDSIZE];
-      BCLine line = currentline(L, fn, nextframe);
-      if (line >= 0) {
-	err_chunkid(buff, strdata(proto_chunkname(funcproto(fn))));
-	lj_str_pushf(L, "%s:%d: %s", buff, line, msg);
-	return;
-      }
-    }
-  }
-  lj_str_pushf(L, "%s", msg);
-}
-
 /* Formatted runtime error message. */
 LJ_NORET LJ_NOINLINE static void err_msgv(lua_State *L, ErrMsg em, ...)
 {
@@ -882,7 +510,7 @@ LJ_NORET LJ_NOINLINE static void err_msgv(lua_State *L, ErrMsg em, ...)
   if (curr_funcisL(L)) L->top = curr_topL(L);
   msg = lj_str_pushvf(L, err2msg(em), argp);
   va_end(argp);
-  err_loc(L, msg, L->base-1, NULL);
+  lj_debug_addloc(L, msg, L->base-1, NULL);
   lj_err_run(L);
 }
 
@@ -898,7 +526,7 @@ LJ_NOINLINE void lj_err_lex(lua_State *L, const char *src, const char *tok,
 {
   char buff[LUA_IDSIZE];
   const char *msg;
-  err_chunkid(buff, src);
+  lj_debug_shortname(buff, src);
   msg = lj_str_pushvf(L, err2msg(em), argp);
   msg = lj_str_pushf(L, "%s:%d: %s", buff, line, msg);
   if (tok)
@@ -910,12 +538,12 @@ LJ_NOINLINE void lj_err_lex(lua_State *L, const char *src, const char *tok,
 LJ_NOINLINE void lj_err_optype(lua_State *L, cTValue *o, ErrMsg opm)
 {
   const char *tname = typename(o);
-  const char *oname = NULL;
   const char *opname = err2msg(opm);
   if (curr_funcisL(L)) {
     GCproto *pt = curr_proto(L);
     const BCIns *pc = cframe_Lpc(L) - 1;
-    const char *kind = getobjname(pt, pc, (BCReg)(o - L->base), &oname);
+    const char *oname = NULL;
+    const char *kind = lj_debug_slotname(pt, pc, (BCReg)(o-L->base), &oname);
     if (kind)
       err_msgv(L, LJ_ERR_BADOPRT, opname, kind, oname, tname);
   }
@@ -967,7 +595,7 @@ LJ_NOINLINE void lj_err_callermsg(lua_State *L, const char *msg)
     }
 #endif
   }
-  err_loc(L, msg, pframe, frame);
+  lj_debug_addloc(L, msg, pframe, frame);
   lj_err_run(L);
 }
 
@@ -993,7 +621,7 @@ LJ_NORET LJ_NOINLINE static void err_argmsg(lua_State *L, int narg,
 					    const char *msg)
 {
   const char *fname = "?";
-  const char *ftype = getfuncname(L, L->base - 1, &fname);
+  const char *ftype = lj_debug_funcname(L, L->base - 1, &fname);
   if (narg < 0 && narg > LUA_REGISTRYINDEX)
     narg = (int)(L->top - L->base) + narg + 1;
   if (ftype && ftype[3] == 'h' && --narg == 0)  /* Check for "method". */
@@ -1066,8 +694,8 @@ LUALIB_API int luaL_typerror(lua_State *L, int narg, const char *xname)
 LUALIB_API void luaL_where(lua_State *L, int level)
 {
   int size;
-  cTValue *frame = lj_err_getframe(L, level, &size);
-  err_loc(L, "", frame, size ? frame+size : NULL);
+  cTValue *frame = lj_debug_frame(L, level, &size);
+  lj_debug_addloc(L, "", frame, size ? frame+size : NULL);
 }
 
 LUALIB_API int luaL_error(lua_State *L, const char *fmt, ...)
diff --git a/src/lj_err.h b/src/lj_err.h
index aabbf490..69ede6d6 100644
--- a/src/lj_err.h
+++ b/src/lj_err.h
@@ -1,5 +1,5 @@
 /*
-** Error handling and debugging support.
+** Error handling.
 ** Copyright (C) 2005-2011 Mike Pall. See Copyright Notice in luajit.h
 */
 
@@ -38,7 +38,4 @@ LJ_FUNC_NORET void lj_err_argv(lua_State *L, int narg, ErrMsg em, ...);
 LJ_FUNC_NORET void lj_err_argtype(lua_State *L, int narg, const char *xname);
 LJ_FUNC_NORET void lj_err_argt(lua_State *L, int narg, int tt);
 
-LJ_FUNC void lj_err_pushloc(lua_State *L, GCproto *pt, BCPos pc);
-LJ_FUNC cTValue *lj_err_getframe(lua_State *L, int level, int *size);
-
 #endif
diff --git a/src/lj_gdbjit.c b/src/lj_gdbjit.c
index 41ee1b33..28e063fb 100644
--- a/src/lj_gdbjit.c
+++ b/src/lj_gdbjit.c
@@ -12,6 +12,7 @@
 
 #include "lj_gc.h"
 #include "lj_err.h"
+#include "lj_debug.h"
 #include "lj_frame.h"
 #include "lj_jit.h"
 #include "lj_dispatch.h"
@@ -728,10 +729,8 @@ void lj_gdbjit_addtrace(jit_State *J, GCtrace *T)
   ctx.spadjp = CFRAME_SIZE_JIT +
 	       (MSize)(parent ? traceref(J, parent)->spadjust : 0);
   ctx.spadj = CFRAME_SIZE_JIT + T->spadjust;
-  if (startpc >= proto_bc(pt) && startpc < proto_bc(pt) + pt->sizebc)
-    ctx.lineno = proto_line(pt, proto_bcpos(pt, startpc));
-  else
-    ctx.lineno = proto_line(pt, 0);  /* Wrong, but better than nothing. */
+  lua_assert(startpc >= proto_bc(pt) && startpc < proto_bc(pt) + pt->sizebc);
+  ctx.lineno = lj_debug_line(pt, proto_bcpos(pt, startpc));
   ctx.filename = strdata(proto_chunkname(pt));
   if (*ctx.filename == '@' || *ctx.filename == '=')
     ctx.filename++;
diff --git a/src/lj_trace.c b/src/lj_trace.c
index bef4558b..6b1dd2f6 100644
--- a/src/lj_trace.c
+++ b/src/lj_trace.c
@@ -12,6 +12,7 @@
 
 #include "lj_gc.h"
 #include "lj_err.h"
+#include "lj_debug.h"
 #include "lj_str.h"
 #include "lj_frame.h"
 #include "lj_state.h"
@@ -103,10 +104,8 @@ static void perftools_addtrace(GCtrace *T)
     name++;
   else
     name = "(string)";
-  if (startpc >= proto_bc(pt) && startpc < proto_bc(pt) + pt->sizebc)
-    lineno = proto_line(pt, proto_bcpos(pt, startpc));
-  else
-    lineno = proto_line(pt, 0);  /* Wrong, but better than nothing. */
+  lua_assert(startpc >= proto_bc(pt) && startpc < proto_bc(pt) + pt->sizebc);
+  lineno = lj_debug_line(pt, proto_bcpos(pt, startpc));
   if (!fp) {
     char fname[40];
     sprintf(fname, "/tmp/perf-%d.map", getpid());
diff --git a/src/ljamalg.c b/src/ljamalg.c
index 3d1f3938..fcfb77ff 100644
--- a/src/ljamalg.c
+++ b/src/ljamalg.c
@@ -38,6 +38,7 @@
 #include "lj_func.c"
 #include "lj_udata.c"
 #include "lj_meta.c"
+#include "lj_debug.c"
 #include "lj_state.c"
 #include "lj_dispatch.c"
 #include "lj_vmevent.c"