text: /*
  ** $Id: ldebug.c $
  ** Debug Interface
  ** See Copyright Notice in lua.h
  */
  
  #define ldebug_c
  #define LUA_CORE
  
  #include "lprefix.h"
  
  
  #include <stdarg.h>
  #include <stddef.h>
  #include <string.h>
  
  #include "lua.h"
  
  #include "lapi.h"
  #include "lcode.h"
  #include "ldebug.h"
  #include "ldo.h"
  #include "lfunc.h"
  #include "lobject.h"
  #include "lopcodes.h"
  #include "lstate.h"
  #include "lstring.h"
  #include "ltable.h"
  #include "ltm.h"
  #include "lvm.h"
  
  
  
  #define noLuaClosure(f)		((f) == NULL || (f)->c.tt == LUA_TCCL)
  
  
  /* Active Lua function (given call info) */
  #define ci_func(ci)		(clLvalue(s2v((ci)->func)))
  
  
  static const char *funcnamefromcode (lua_State *L, CallInfo *ci,
                                      const char **name);
  
  
  static int currentpc (CallInfo *ci) {
    lua_assert(isLua(ci));
    return pcRel(ci->u.l.savedpc, ci_func(ci)->p);
  }
  
  
  /*
  ** Get a "base line" to find the line corresponding to an instruction.
  ** For that, search the array of absolute line info for the largest saved
  ** instruction smaller or equal to the wanted instruction. A special
  ** case is when there is no absolute info or the instruction is before
  ** the first absolute one.
  */
  static int getbaseline (const Proto *f, int pc, int *basepc) {
    if (f->sizeabslineinfo == 0 || pc < f->abslineinfo[0].pc) {
      *basepc = -1;  /* start from the beginning */
      return f->linedefined;
    }
    else {
      unsigned int i;
      if (pc >= f->abslineinfo[f->sizeabslineinfo - 1].pc)
        i = f->sizeabslineinfo - 1;  /* instruction is after last saved one */
      else {  /* binary search */
        unsigned int j = f->sizeabslineinfo - 1;  /* pc < anchorlines[j] */
        i = 0;  /* abslineinfo[i] <= pc */
        while (i < j - 1) {
          unsigned int m = (j + i) / 2;
          if (pc >= f->abslineinfo[m].pc)
            i = m;
          else
            j = m;
        }
      }
      *basepc = f->abslineinfo[i].pc;
      return f->abslineinfo[i].line;
    }
  }
  
  
  /*
  ** Get the line corresponding to instruction 'pc' in function 'f';
  ** first gets a base line and from there does the increments until
  ** the desired instruction.
  */
  int luaG_getfuncline (const Proto *f, int pc) {
    if (f->lineinfo == NULL)  /* no debug information? */
      return -1;
    else {
      int basepc;
      int baseline = getbaseline(f, pc, &basepc);
      while (basepc++ < pc) {  /* walk until given instruction */
        lua_assert(f->lineinfo[basepc] != ABSLINEINFO);
        baseline += f->lineinfo[basepc];  /* correct line */
      }
      return baseline;
    }
  }
  
  
  static int currentline (CallInfo *ci) {
    return luaG_getfuncline(ci_func(ci)->p, currentpc(ci));
  }
  
  
  /*
  ** This function can be called asynchronously (e.g. during a signal),
  ** under "reasonable" assumptions. A new 'ci' is completely linked
  ** in the list before it becomes part of the "active" list, and
  ** we assume that pointers are atomic (see comment in next function).
  ** (If we traverse one more item, there is no problem. If we traverse
  ** one less item, the worst that can happen is that the signal will
  ** not interrupt the script.)
  */
  static void settraps (CallInfo *ci) {
    for (; ci != NULL; ci = ci->previous)
      if (isLua(ci))
        ci->u.l.trap = 1;
  }
  
  
  /*
  ** This function can be called asynchronously (e.g. during a signal),
  ** under "reasonable" assumptions.
  ** Fields 'oldpc', 'basehookcount', and 'hookcount' (set by
  ** 'resethookcount') are for debug only, and it is no problem if they
  ** get arbitrary values (causes at most one wrong hook call). 'hookmask'
  ** is an atomic value. We assume that pointers are atomic too (e.g., gcc
  ** ensures that for all platforms where it runs). Moreover, 'hook' is
  ** always checked before being called (see 'luaD_hook').
  */
  LUA_API void lua_sethook (lua_State *L, lua_Hook func, int mask, int count) {
    if (func == NULL || mask == 0) {  /* turn off hooks? */
      mask = 0;
      func = NULL;
    }
    if (isLua(L->ci))
      L->oldpc = L->ci->u.l.savedpc;
    L->hook = func;
    L->basehookcount = count;
    resethookcount(L);
    L->hookmask = cast_byte(mask);
    if (mask & (LUA_MASKCALL | LUA_MASKRET | LUA_MASKLINE | LUA_MASKCOUNT))
      settraps(L->ci);  /* to trace inside 'luaV_execute' */
  }
  
  
  LUA_API lua_Hook lua_gethook (lua_State *L) {
    return L->hook;
  }
  
  
  LUA_API int lua_gethookmask (lua_State *L) {
    return L->hookmask;
  }
  
  
  LUA_API int lua_gethookcount (lua_State *L) {
    return L->basehookcount;
  }
  
  
  LUA_API int lua_getstack (lua_State *L, int level, lua_Debug *ar) {
    int status;
    CallInfo *ci;
    if (level < 0) return 0;  /* invalid (negative) level */
    lua_lock(L);
    for (ci = L->ci; level > 0 && ci != &L->base_ci; ci = ci->previous)
      level--;
    if (level == 0 && ci != &L->base_ci) {  /* level found? */
      status = 1;
      ar->i_ci = ci;
    }
    else status = 0;  /* no such level */
    lua_unlock(L);
    return status;
  }
  
  
  static const char *upvalname (const Proto *p, int uv) {
    TString *s = check_exp(uv < p->sizeupvalues, p->upvalues[uv].name);
    if (s == NULL) return "?";
    else return getstr(s);
  }
  
  
  static const char *findvararg (CallInfo *ci, int n, StkId *pos) {
    if (clLvalue(s2v(ci->func))->p->is_vararg) {
      int nextra = ci->u.l.nextraargs;
      if (n <= nextra) {
        *pos = ci->func - nextra + (n - 1);
        return "(vararg)";  /* generic name for any vararg */
      }
    }
    return NULL;  /* no such vararg */
  }
  
  
  const char *luaG_findlocal (lua_State *L, CallInfo *ci, int n, StkId *pos) {
    StkId base = ci->func + 1;
    const char *name = NULL;
    if (isLua(ci)) {
      if (n < 0)  /* access to vararg values? */
        return findvararg(ci, -n, pos);
      else
        name = luaF_getlocalname(ci_func(ci)->p, n, currentpc(ci));
    }
    if (name == NULL) {  /* no 'standard' name? */
      StkId limit = (ci == L->ci) ? L->top : ci->next->func;
      if (limit - base >= n && n > 0) {  /* is 'n' inside 'ci' stack? */
        /* generic name for any valid slot */
        name = isLua(ci) ? "(temporary)" : "(C temporary)";
      }
      else
        return NULL;  /* no name */
    }
    if (pos)
    *pos = base + (n - 1);
    return name;
  }
  
  
  LUA_API const char *lua_getlocal (lua_State *L, const lua_Debug *ar, int n) {
    const char *name;
    lua_lock(L);
    if (ar == NULL) {  /* information about non-active function? */
      if (!isLfunction(s2v(L->top - 1)))  /* not a Lua function? */
        name = NULL;
      else  /* consider live variables at function start (parameters) */
        name = luaF_getlocalname(clLvalue(s2v(L->top - 1))->p, n, 0);
    }
    else {  /* active function; get information through 'ar' */
      StkId pos = NULL;  /* to avoid warnings */
      name = luaG_findlocal(L, ar->i_ci, n, &pos);
      if (name) {
        setobjs2s(L, L->top, pos);
        api_incr_top(L);
      }
    }
    lua_unlock(L);
    return name;
  }
  
  
  LUA_API const char *lua_setlocal (lua_State *L, const lua_Debug *ar, int n) {
    StkId pos = NULL;  /* to avoid warnings */
    const char *name;
    lua_lock(L);
    name = luaG_findlocal(L, ar->i_ci, n, &pos);
    if (name) {
      setobjs2s(L, pos, L->top - 1);
      L->top--;  /* pop value */
    }
    lua_unlock(L);
    return name;
  }
  
  
  static void funcinfo (lua_Debug *ar, Closure *cl) {
    if (noLuaClosure(cl)) {
      ar->source = "=[C]";
      ar->srclen = LL("=[C]");
      ar->linedefined = -1;
      ar->lastlinedefined = -1;
      ar->what = "C";
    }
    else {
      const Proto *p = cl->l.p;
      if (p->source) {
        ar->source = getstr(p->source);
        ar->srclen = tsslen(p->source);
      }
      else {
        ar->source = "=?";
        ar->srclen = LL("=?");
      }
      ar->linedefined = p->linedefined;
      ar->lastlinedefined = p->lastlinedefined;
      ar->what = (ar->linedefined == 0) ? "main" : "Lua";
    }
    luaO_chunkid(ar->short_src, ar->source, ar->srclen);
  }
  
  
  static int nextline (const Proto *p, int currentline, int pc) {
    if (p->lineinfo[pc] != ABSLINEINFO)
      return currentline + p->lineinfo[pc];
    else
      return luaG_getfuncline(p, pc);
  }
  
  
  static void collectvalidlines (lua_State *L, Closure *f) {
    if (noLuaClosure(f)) {
      setnilvalue(s2v(L->top));
      api_incr_top(L);
    }
    else {
      int i;
      TValue v;
      const Proto *p = f->l.p;
      int currentline = p->linedefined;
      Table *t = luaH_new(L);  /* new table to store active lines */
      sethvalue2s(L, L->top, t);  /* push it on stack */
      api_incr_top(L);
      setbvalue(&v, 1);  /* boolean 'true' to be the value of all indices */
      for (i = 0; i < p->sizelineinfo; i++) {  /* for all lines with code */
        currentline = nextline(p, currentline, i);
        luaH_setint(L, t, currentline, &v);  /* table[line] = true */
      }
    }
  }
  
  
  static const char *getfuncname (lua_State *L, CallInfo *ci, const char **name) {
    if (ci == NULL)  /* no 'ci'? */
      return NULL;  /* no info */
    else if (ci->callstatus & CIST_FIN) {  /* is this a finalizer? */
      *name = "__gc";
      return "metamethod";  /* report it as such */
    }
    /* calling function is a known Lua function? */
    else if (!(ci->callstatus & CIST_TAIL) && isLua(ci->previous))
      return funcnamefromcode(L, ci->previous, name);
    else return NULL;  /* no way to find a name */
  }
  
  
  static int auxgetinfo (lua_State *L, const char *what, lua_Debug *ar,
                         Closure *f, CallInfo *ci) {
    int status = 1;
    for (; *what; what++) {
      switch (*what) {
        case 'S': {
          funcinfo(ar, f);
          break;
        }
        case 'l': {
          ar->currentline = (ci && isLua(ci)) ? currentline(ci) : -1;
          break;
        }
        case 'u': {
          ar->nups = (f == NULL) ? 0 : f->c.nupvalues;
          if (noLuaClosure(f)) {
            ar->isvararg = 1;
            ar->nparams = 0;
          }
          else {
            ar->isvararg = f->l.p->is_vararg;
            ar->nparams = f->l.p->numparams;
          }
          break;
        }
        case 't': {
          ar->istailcall = (ci) ? ci->callstatus & CIST_TAIL : 0;
          break;
        }
        case 'n': {
          ar->namewhat = getfuncname(L, ci, &ar->name);
          if (ar->namewhat == NULL) {
            ar->namewhat = "";  /* not found */
            ar->name = NULL;
          }
          break;
        }
        case 'r': {
          if (ci == NULL || !(ci->callstatus & CIST_TRAN))
            ar->ftransfer = ar->ntransfer = 0;
          else {
            ar->ftransfer = ci->u2.transferinfo.ftransfer;
            ar->ntransfer = ci->u2.transferinfo.ntransfer;
          }
        }
        case 'L':
        case 'f':  /* handled by lua_getinfo */
          break;
        default: status = 0;  /* invalid option */
      }
    }
    return status;
  }
  
  
  LUA_API int lua_getinfo (lua_State *L, const char *what, lua_Debug *ar) {
    int status;
    Closure *cl;
    CallInfo *ci;
    TValue *func;
    lua_lock(L);
    if (*what == '>') {
      ci = NULL;
      func = s2v(L->top - 1);
      api_check(L, ttisfunction(func), "function expected");
      what++;  /* skip the '>' */
      L->top--;  /* pop function */
    }
    else {
      ci = ar->i_ci;
      func = s2v(ci->func);
      lua_assert(ttisfunction(func));
    }
    cl = ttisclosure(func) ? clvalue(func) : NULL;
    status = auxgetinfo(L, what, ar, cl, ci);
    if (strchr(what, 'f')) {
      setobj2s(L, L->top, func);
      api_incr_top(L);
    }
    if (strchr(what, 'L'))
      collectvalidlines(L, cl);
    lua_unlock(L);
    return status;
  }
  
  
  /*
  ** {======================================================
  ** Symbolic Execution
  ** =======================================================
  */
  
  static const char *getobjname (const Proto *p, int lastpc, int reg,
                                 const char **name);
  
  
  /*
  ** Find a "name" for the constant 'c'.
  */
  static void kname (const Proto *p, int c, const char **name) {
    TValue *kvalue = &p->k[c];
    *name = (ttisstring(kvalue)) ? svalue(kvalue) : "?";
  }
  
  
  /*
  ** Find a "name" for the register 'c'.
  */
  static void rname (const Proto *p, int pc, int c, const char **name) {
    const char *what = getobjname(p, pc, c, name); /* search for 'c' */
    if (!(what && *what == 'c'))  /* did not find a constant name? */
      *name = "?";
  }
  
  
  /*
  ** Find a "name" for a 'C' value in an RK instruction.
  */
  static void rkname (const Proto *p, int pc, Instruction i, const char **name) {
    int c = GETARG_C(i);  /* key index */
    if (GETARG_k(i))  /* is 'c' a constant? */
      kname(p, c, name);
    else  /* 'c' is a register */
      rname(p, pc, c, name);
  }
  
  
  static int filterpc (int pc, int jmptarget) {
    if (pc < jmptarget)  /* is code conditional (inside a jump)? */
      return -1;  /* cannot know who sets that register */
    else return pc;  /* current position sets that register */
  }
  
  
  /*
  ** try to find last instruction before 'lastpc' that modified register 'reg'
  */
  static int findsetreg (const Proto *p, int lastpc, int reg) {
    int pc;
    int setreg = -1;  /* keep last instruction that changed 'reg' */
    int jmptarget = 0;  /* any code before this address is conditional */
    for (pc = 0; pc < lastpc; pc++) {
      Instruction i = p->code[pc];
      OpCode op = GET_OPCODE(i);
      int a = GETARG_A(i);
      int change;  /* true if current instruction changed 'reg' */
      switch (op) {
        case OP_LOADNIL: {  /* set registers from 'a' to 'a+b' */
          int b = GETARG_B(i);
          change = (a <= reg && reg <= a + b);
          break;
        }
        case OP_TFORCALL: {  /* affect all regs above its base */
          change = (reg >= a + 2);
          break;
        }
        case OP_CALL:
        case OP_TAILCALL: {  /* affect all registers above base */
          change = (reg >= a);
          break;
        }
        case OP_JMP: {  /* doesn't change registers, but changes 'jmptarget' */
          int b = GETARG_sJ(i);
          int dest = pc + 1 + b;
          /* jump does not skip 'lastpc' and is larger than current one? */
          if (dest <= lastpc && dest > jmptarget)
            jmptarget = dest;  /* update 'jmptarget' */
          change = 0;
          break;
        }
        default:  /* any instruction that sets A */
          change = (testAMode(op) && reg == a);
          break;
      }
      if (change)
        setreg = filterpc(pc, jmptarget);
    }
    return setreg;
  }
  
  
  /*
  ** Check whether table being indexed by instruction 'i' is the
  ** environment '_ENV'
  */
  static const char *gxf (const Proto *p, int pc, Instruction i, int isup) {
    int t = GETARG_B(i);  /* table index */
    const char *name;  /* name of indexed variable */
    if (isup)  /* is an upvalue? */
      name = upvalname(p, t);
    else
      getobjname(p, pc, t, &name);
    return (name && strcmp(name, LUA_ENV) == 0) ? "global" : "field";
  }
  
  
   const char *getobjname (const Proto *p, int lastpc, int reg,
                           const char **name) {
    int pc;
    *name = luaF_getlocalname(p, reg + 1, lastpc);
    if (*name)  /* is a local? */
      return "local";
    /* else try symbolic execution */
    pc = findsetreg(p, lastpc, reg);
    if (pc != -1) {  /* could find instruction? */
      Instruction i = p->code[pc];
      OpCode op = GET_OPCODE(i);
      switch (op) {
        case OP_MOVE: {
          int b = GETARG_B(i);  /* move from 'b' to 'a' */
          if (b < GETARG_A(i))
            return getobjname(p, pc, b, name);  /* get name for 'b' */
          break;
        }
        case OP_GETTABUP: {
          int k = GETARG_C(i);  /* key index */
          kname(p, k, name);
          return gxf(p, pc, i, 1);
        }
        case OP_GETTABLE: {
          int k = GETARG_C(i);  /* key index */
          rname(p, pc, k, name);
          return gxf(p, pc, i, 0);
        }
        case OP_GETI: {
          *name = "integer index";
          return "field";
        }
        case OP_GETFIELD: {
          int k = GETARG_C(i);  /* key index */
          kname(p, k, name);
          return gxf(p, pc, i, 0);
        }
        case OP_GETUPVAL: {
          *name = upvalname(p, GETARG_B(i));
          return "upvalue";
        }
        case OP_LOADK:
        case OP_LOADKX: {
          int b = (op == OP_LOADK) ? GETARG_Bx(i)
                                   : GETARG_Ax(p->code[pc + 1]);
          if (ttisstring(&p->k[b])) {
            *name = svalue(&p->k[b]);
            return "constant";
          }
          break;
        }
        case OP_SELF: {
          rkname(p, pc, i, name);
          return "method";
        }
        default: break;  /* go through to return NULL */
      }
    }
    return NULL;  /* could not find reasonable name */
  }
  
  
  /*
  ** Try to find a name for a function based on the code that called it.
  ** (Only works when function was called by a Lua function.)
  ** Returns what the name is (e.g., "for iterator", "method",
  ** "metamethod") and sets '*name' to point to the name.
  */
  static const char *funcnamefromcode (lua_State *L, CallInfo *ci,
                                       const char **name) {
    TMS tm = (TMS)0;  /* (initial value avoids warnings) */
    const Proto *p = ci_func(ci)->p;  /* calling function */
    int pc = currentpc(ci);  /* calling instruction index */
    Instruction i = p->code[pc];  /* calling instruction */
    if (ci->callstatus & CIST_HOOKED) {  /* was it called inside a hook? */
      *name = "?";
      return "hook";
    }
    switch (GET_OPCODE(i)) {
      case OP_CALL:
      case OP_TAILCALL:
        return getobjname(p, pc, GETARG_A(i), name);  /* get function name */
      case OP_TFORCALL: {  /* for iterator */
        *name = "for iterator";
         return "for iterator";
      }
      /* other instructions can do calls through metamethods */
      case OP_SELF: case OP_GETTABUP: case OP_GETTABLE:
      case OP_GETI: case OP_GETFIELD:
        tm = TM_INDEX;
        break;
      case OP_SETTABUP: case OP_SETTABLE: case OP_SETI: case OP_SETFIELD:
        tm = TM_NEWINDEX;
        break;
      case OP_ADDI: case OP_SUBI: case OP_MULI: case OP_MODI:
      case OP_POWI: case OP_DIVI: case OP_IDIVI: {
        int offset = GET_OPCODE(i) - OP_ADDI;  /* ORDER OP */
        tm = cast(TMS, offset + TM_ADD);  /* ORDER TM */
        break;
      }
      case OP_ADDK: case OP_SUBK: case OP_MULK: case OP_MODK:
      case OP_POWK: case OP_DIVK: case OP_IDIVK:
      case OP_BANDK: case OP_BORK: case OP_BXORK: {
        int offset = GET_OPCODE(i) - OP_ADDK;  /* ORDER OP */
        tm = cast(TMS, offset + TM_ADD);  /* ORDER TM */
        break;
      }
      case OP_ADD: case OP_SUB: case OP_MUL: case OP_MOD:
      case OP_POW: case OP_DIV: case OP_IDIV: case OP_BAND:
      case OP_BOR: case OP_BXOR: case OP_SHL: case OP_SHR: {
        int offset = GET_OPCODE(i) - OP_ADD;  /* ORDER OP */
        tm = cast(TMS, offset + TM_ADD);  /* ORDER TM */
        break;
      }
      case OP_UNM: tm = TM_UNM; break;
      case OP_BNOT: tm = TM_BNOT; break;
      case OP_LEN: tm = TM_LEN; break;
      case OP_CONCAT: tm = TM_CONCAT; break;
      case OP_EQ: tm = TM_EQ; break;
      case OP_LT: case OP_LE: case OP_LTI: case OP_LEI:
        *name = "order";  /* '<=' can call '__lt', etc. */
        return "metamethod";
      case OP_SHRI: case OP_SHLI:
        *name = "shift";
        return "metamethod";
      default:
        return NULL;  /* cannot find a reasonable name */
    }
    *name = getstr(G(L)->tmname[tm]) + 2;
    return "metamethod";
  }
  
  /* }====================================================== */
  
  
  
  /*
  ** The subtraction of two potentially unrelated pointers is
  ** not ISO C, but it should not crash a program; the subsequent
  ** checks are ISO C and ensure a correct result.
  */
  static int isinstack (CallInfo *ci, const TValue *o) {
    StkId base = ci->func + 1;
    ptrdiff_t i = cast(StkId, o) - base;
    return (0 <= i && i < (ci->top - base) && s2v(base + i) == o);
  }
  
  
  /*
  ** Checks whether value 'o' came from an upvalue. (That can only happen
  ** with instructions OP_GETTABUP/OP_SETTABUP, which operate directly on
  ** upvalues.)
  */
  static const char *getupvalname (CallInfo *ci, const TValue *o,
                                   const char **name) {
    LClosure *c = ci_func(ci);
    int i;
    for (i = 0; i < c->nupvalues; i++) {
      if (c->upvals[i]->v == o) {
        *name = upvalname(c->p, i);
        return "upvalue";
      }
    }
    return NULL;
  }
  
  
  static const char *varinfo (lua_State *L, const TValue *o) {
    const char *name = NULL;  /* to avoid warnings */
    CallInfo *ci = L->ci;
    const char *kind = NULL;
    if (isLua(ci)) {
      kind = getupvalname(ci, o, &name);  /* check whether 'o' is an upvalue */
      if (!kind && isinstack(ci, o))  /* no? try a register */
        kind = getobjname(ci_func(ci)->p, currentpc(ci),
                          cast_int(cast(StkId, o) - (ci->func + 1)), &name);
    }
    return (kind) ? luaO_pushfstring(L, " (%s '%s')", kind, name) : "";
  }
  
  
  l_noret luaG_typeerror (lua_State *L, const TValue *o, const char *op) {
    const char *t = luaT_objtypename(L, o);
    luaG_runerror(L, "attempt to %s a %s value%s", op, t, varinfo(L, o));
  }
  
  
  l_noret luaG_forerror (lua_State *L, const TValue *o, const char *what) {
    luaG_runerror(L, "bad 'for' %s (number expected, got %s)",
                     what, luaT_objtypename(L, o));
  }
  
  
  l_noret luaG_concaterror (lua_State *L, const TValue *p1, const TValue *p2) {
    if (ttisstring(p1) || cvt2str(p1)) p1 = p2;
    luaG_typeerror(L, p1, "concatenate");
  }
  
  
  l_noret luaG_opinterror (lua_State *L, const TValue *p1,
                           const TValue *p2, const char *msg) {
    if (!ttisnumber(p1))  /* first operand is wrong? */
      p2 = p1;  /* now second is wrong */
    luaG_typeerror(L, p2, msg);
  }
  
  
  /*
  ** Error when both values are convertible to numbers, but not to integers
  */
  l_noret luaG_tointerror (lua_State *L, const TValue *p1, const TValue *p2) {
    lua_Integer temp;
    if (!tointegerns(p1, &temp))
      p2 = p1;
    luaG_runerror(L, "number%s has no integer representation", varinfo(L, p2));
  }
  
  
  l_noret luaG_ordererror (lua_State *L, const TValue *p1, const TValue *p2) {
    const char *t1 = luaT_objtypename(L, p1);
    const char *t2 = luaT_objtypename(L, p2);
    if (strcmp(t1, t2) == 0)
      luaG_runerror(L, "attempt to compare two %s values", t1);
    else
      luaG_runerror(L, "attempt to compare %s with %s", t1, t2);
  }
  
  
  /* add src:line information to 'msg' */
  const char *luaG_addinfo (lua_State *L, const char *msg, TString *src,
                                          int line) {
    char buff[LUA_IDSIZE];
    if (src)
      luaO_chunkid(buff, getstr(src), tsslen(src));
    else {  /* no source available; use "?" instead */
      buff[0] = '?'; buff[1] = '\0';
    }
    return luaO_pushfstring(L, "%s:%d: %s", buff, line, msg);
  }
  
  
  l_noret luaG_errormsg (lua_State *L) {
    if (L->hookmask & LUA_MASKEXCEPTION)
      luaD_hook(L, LUA_HOOKEXCEPTION, -1, 0, 0);
    if (L->errfunc != 0) {  /* is there an error handling function? */
      StkId errfunc = restorestack(L, L->errfunc);
      lua_assert(ttisfunction(s2v(errfunc)));
      setobjs2s(L, L->top, L->top - 1);  /* move argument */
      setobjs2s(L, L->top - 1, errfunc);  /* push function */
      L->top++;  /* assume EXTRA_STACK */
      luaD_callnoyield(L, L->top - 2, 1);  /* call it */
    }
    luaD_throw(L, LUA_ERRRUN);
  }
  
  
  l_noret luaG_runerror (lua_State *L, const char *fmt, ...) {
    CallInfo *ci = L->ci;
    const char *msg;
    va_list argp;
    luaC_checkGC(L);  /* error message uses memory */
    va_start(argp, fmt);
    msg = luaO_pushvfstring(L, fmt, argp);  /* format message */
    va_end(argp);
    if (isLua(ci))  /* if Lua function, add source:line information */
      luaG_addinfo(L, msg, ci_func(ci)->p->source, currentline(ci));
    luaG_errormsg(L);
  }
  
  
  /*
  ** Check whether new instruction 'newpc' is in a different line from
  ** previous instruction 'oldpc'.
  */
  static int changedline (const Proto *p, int oldpc, int newpc) {
    while (oldpc++ < newpc) {
      if (p->lineinfo[oldpc] != 0)
        return (luaG_getfuncline(p, oldpc - 1) != luaG_getfuncline(p, newpc));
    }
    return 0;  /* no line changes in the way */
  }
  
  
  int luaG_traceexec (lua_State *L, const Instruction *pc) {
    CallInfo *ci = L->ci;
    lu_byte mask = L->hookmask;
    int counthook;
    if (!(mask & (LUA_MASKLINE | LUA_MASKCOUNT))) {  /* no hooks? */
      ci->u.l.trap = 0;  /* don't need to stop again */
      return 0;  /* turn off 'trap' */
    }
    pc++;  /* reference is always next instruction */
    ci->u.l.savedpc = pc;  /* save 'pc' */
    counthook = (--L->hookcount == 0 && (mask & LUA_MASKCOUNT));
    if (counthook)
      resethookcount(L);  /* reset count */
    else if (!(mask & LUA_MASKLINE))
      return 1;  /* no line hook and count != 0; nothing to be done now */
    if (ci->callstatus & CIST_HOOKYIELD) {  /* called hook last time? */
      ci->callstatus &= ~CIST_HOOKYIELD;  /* erase mark */
      return 1;  /* do not call hook again (VM yielded, so it did not move) */
    }
    if (!isIT(*(ci->u.l.savedpc - 1)))
      L->top = ci->top;  /* prepare top */
    if (counthook)
      luaD_hook(L, LUA_HOOKCOUNT, -1, 0, 0);  /* call count hook */
    if (mask & LUA_MASKLINE) {
      const Proto *p = ci_func(ci)->p;
      int npci = pcRel(pc, p);
      if (npci == 0 ||  /* call linehook when enter a new function, */
          pc <= L->oldpc ||  /* when jump back (loop), or when */
          changedline(p, pcRel(L->oldpc, p), npci)) {  /* enter new line */
        int newline = luaG_getfuncline(p, npci);
        luaD_hook(L, LUA_HOOKLINE, newline, 0, 0);  /* call line hook */
      }
      L->oldpc = pc;  /* 'pc' of last call to line hook */
    }
    if (L->status == LUA_YIELD) {  /* did hook yield? */
      if (counthook)
        L->hookcount = 1;  /* undo decrement to zero */
      ci->u.l.savedpc--;  /* undo increment (resume will increment it again) */
      ci->callstatus |= CIST_HOOKYIELD;  /* mark that it yielded */
      luaD_throw(L, LUA_YIELD);
    }
    return 1;  /* keep 'trap' on */
  }
  
  