xref: /freebsd/contrib/lua/src/ldebug.c (revision 4f52dfbb8d6c4d446500c5b097e3806ec219fbd4)
1 /*
2 ** $Id: ldebug.c,v 2.121 2016/10/19 12:32:10 roberto Exp $
3 ** Debug Interface
4 ** See Copyright Notice in lua.h
5 */
6 
7 #define ldebug_c
8 #define LUA_CORE
9 
10 #include "lprefix.h"
11 
12 
13 #include <stdarg.h>
14 #include <stddef.h>
15 #include <string.h>
16 
17 #include "lua.h"
18 
19 #include "lapi.h"
20 #include "lcode.h"
21 #include "ldebug.h"
22 #include "ldo.h"
23 #include "lfunc.h"
24 #include "lobject.h"
25 #include "lopcodes.h"
26 #include "lstate.h"
27 #include "lstring.h"
28 #include "ltable.h"
29 #include "ltm.h"
30 #include "lvm.h"
31 
32 
33 
34 #define noLuaClosure(f)		((f) == NULL || (f)->c.tt == LUA_TCCL)
35 
36 
37 /* Active Lua function (given call info) */
38 #define ci_func(ci)		(clLvalue((ci)->func))
39 
40 
41 static const char *funcnamefromcode (lua_State *L, CallInfo *ci,
42                                     const char **name);
43 
44 
45 static int currentpc (CallInfo *ci) {
46   lua_assert(isLua(ci));
47   return pcRel(ci->u.l.savedpc, ci_func(ci)->p);
48 }
49 
50 
51 static int currentline (CallInfo *ci) {
52   return getfuncline(ci_func(ci)->p, currentpc(ci));
53 }
54 
55 
56 /*
57 ** If function yielded, its 'func' can be in the 'extra' field. The
58 ** next function restores 'func' to its correct value for debugging
59 ** purposes. (It exchanges 'func' and 'extra'; so, when called again,
60 ** after debugging, it also "re-restores" ** 'func' to its altered value.
61 */
62 static void swapextra (lua_State *L) {
63   if (L->status == LUA_YIELD) {
64     CallInfo *ci = L->ci;  /* get function that yielded */
65     StkId temp = ci->func;  /* exchange its 'func' and 'extra' values */
66     ci->func = restorestack(L, ci->extra);
67     ci->extra = savestack(L, temp);
68   }
69 }
70 
71 
72 /*
73 ** This function can be called asynchronously (e.g. during a signal).
74 ** Fields 'oldpc', 'basehookcount', and 'hookcount' (set by
75 ** 'resethookcount') are for debug only, and it is no problem if they
76 ** get arbitrary values (causes at most one wrong hook call). 'hookmask'
77 ** is an atomic value. We assume that pointers are atomic too (e.g., gcc
78 ** ensures that for all platforms where it runs). Moreover, 'hook' is
79 ** always checked before being called (see 'luaD_hook').
80 */
81 LUA_API void lua_sethook (lua_State *L, lua_Hook func, int mask, int count) {
82   if (func == NULL || mask == 0) {  /* turn off hooks? */
83     mask = 0;
84     func = NULL;
85   }
86   if (isLua(L->ci))
87     L->oldpc = L->ci->u.l.savedpc;
88   L->hook = func;
89   L->basehookcount = count;
90   resethookcount(L);
91   L->hookmask = cast_byte(mask);
92 }
93 
94 
95 LUA_API lua_Hook lua_gethook (lua_State *L) {
96   return L->hook;
97 }
98 
99 
100 LUA_API int lua_gethookmask (lua_State *L) {
101   return L->hookmask;
102 }
103 
104 
105 LUA_API int lua_gethookcount (lua_State *L) {
106   return L->basehookcount;
107 }
108 
109 
110 LUA_API int lua_getstack (lua_State *L, int level, lua_Debug *ar) {
111   int status;
112   CallInfo *ci;
113   if (level < 0) return 0;  /* invalid (negative) level */
114   lua_lock(L);
115   for (ci = L->ci; level > 0 && ci != &L->base_ci; ci = ci->previous)
116     level--;
117   if (level == 0 && ci != &L->base_ci) {  /* level found? */
118     status = 1;
119     ar->i_ci = ci;
120   }
121   else status = 0;  /* no such level */
122   lua_unlock(L);
123   return status;
124 }
125 
126 
127 static const char *upvalname (Proto *p, int uv) {
128   TString *s = check_exp(uv < p->sizeupvalues, p->upvalues[uv].name);
129   if (s == NULL) return "?";
130   else return getstr(s);
131 }
132 
133 
134 static const char *findvararg (CallInfo *ci, int n, StkId *pos) {
135   int nparams = clLvalue(ci->func)->p->numparams;
136   if (n >= cast_int(ci->u.l.base - ci->func) - nparams)
137     return NULL;  /* no such vararg */
138   else {
139     *pos = ci->func + nparams + n;
140     return "(*vararg)";  /* generic name for any vararg */
141   }
142 }
143 
144 
145 static const char *findlocal (lua_State *L, CallInfo *ci, int n,
146                               StkId *pos) {
147   const char *name = NULL;
148   StkId base;
149   if (isLua(ci)) {
150     if (n < 0)  /* access to vararg values? */
151       return findvararg(ci, -n, pos);
152     else {
153       base = ci->u.l.base;
154       name = luaF_getlocalname(ci_func(ci)->p, n, currentpc(ci));
155     }
156   }
157   else
158     base = ci->func + 1;
159   if (name == NULL) {  /* no 'standard' name? */
160     StkId limit = (ci == L->ci) ? L->top : ci->next->func;
161     if (limit - base >= n && n > 0)  /* is 'n' inside 'ci' stack? */
162       name = "(*temporary)";  /* generic name for any valid slot */
163     else
164       return NULL;  /* no name */
165   }
166   *pos = base + (n - 1);
167   return name;
168 }
169 
170 
171 LUA_API const char *lua_getlocal (lua_State *L, const lua_Debug *ar, int n) {
172   const char *name;
173   lua_lock(L);
174   swapextra(L);
175   if (ar == NULL) {  /* information about non-active function? */
176     if (!isLfunction(L->top - 1))  /* not a Lua function? */
177       name = NULL;
178     else  /* consider live variables at function start (parameters) */
179       name = luaF_getlocalname(clLvalue(L->top - 1)->p, n, 0);
180   }
181   else {  /* active function; get information through 'ar' */
182     StkId pos = NULL;  /* to avoid warnings */
183     name = findlocal(L, ar->i_ci, n, &pos);
184     if (name) {
185       setobj2s(L, L->top, pos);
186       api_incr_top(L);
187     }
188   }
189   swapextra(L);
190   lua_unlock(L);
191   return name;
192 }
193 
194 
195 LUA_API const char *lua_setlocal (lua_State *L, const lua_Debug *ar, int n) {
196   StkId pos = NULL;  /* to avoid warnings */
197   const char *name;
198   lua_lock(L);
199   swapextra(L);
200   name = findlocal(L, ar->i_ci, n, &pos);
201   if (name) {
202     setobjs2s(L, pos, L->top - 1);
203     L->top--;  /* pop value */
204   }
205   swapextra(L);
206   lua_unlock(L);
207   return name;
208 }
209 
210 
211 static void funcinfo (lua_Debug *ar, Closure *cl) {
212   if (noLuaClosure(cl)) {
213     ar->source = "=[C]";
214     ar->linedefined = -1;
215     ar->lastlinedefined = -1;
216     ar->what = "C";
217   }
218   else {
219     Proto *p = cl->l.p;
220     ar->source = p->source ? getstr(p->source) : "=?";
221     ar->linedefined = p->linedefined;
222     ar->lastlinedefined = p->lastlinedefined;
223     ar->what = (ar->linedefined == 0) ? "main" : "Lua";
224   }
225   luaO_chunkid(ar->short_src, ar->source, LUA_IDSIZE);
226 }
227 
228 
229 static void collectvalidlines (lua_State *L, Closure *f) {
230   if (noLuaClosure(f)) {
231     setnilvalue(L->top);
232     api_incr_top(L);
233   }
234   else {
235     int i;
236     TValue v;
237     int *lineinfo = f->l.p->lineinfo;
238     Table *t = luaH_new(L);  /* new table to store active lines */
239     sethvalue(L, L->top, t);  /* push it on stack */
240     api_incr_top(L);
241     setbvalue(&v, 1);  /* boolean 'true' to be the value of all indices */
242     for (i = 0; i < f->l.p->sizelineinfo; i++)  /* for all lines with code */
243       luaH_setint(L, t, lineinfo[i], &v);  /* table[line] = true */
244   }
245 }
246 
247 
248 static const char *getfuncname (lua_State *L, CallInfo *ci, const char **name) {
249   if (ci == NULL)  /* no 'ci'? */
250     return NULL;  /* no info */
251   else if (ci->callstatus & CIST_FIN) {  /* is this a finalizer? */
252     *name = "__gc";
253     return "metamethod";  /* report it as such */
254   }
255   /* calling function is a known Lua function? */
256   else if (!(ci->callstatus & CIST_TAIL) && isLua(ci->previous))
257     return funcnamefromcode(L, ci->previous, name);
258   else return NULL;  /* no way to find a name */
259 }
260 
261 
262 static int auxgetinfo (lua_State *L, const char *what, lua_Debug *ar,
263                        Closure *f, CallInfo *ci) {
264   int status = 1;
265   for (; *what; what++) {
266     switch (*what) {
267       case 'S': {
268         funcinfo(ar, f);
269         break;
270       }
271       case 'l': {
272         ar->currentline = (ci && isLua(ci)) ? currentline(ci) : -1;
273         break;
274       }
275       case 'u': {
276         ar->nups = (f == NULL) ? 0 : f->c.nupvalues;
277         if (noLuaClosure(f)) {
278           ar->isvararg = 1;
279           ar->nparams = 0;
280         }
281         else {
282           ar->isvararg = f->l.p->is_vararg;
283           ar->nparams = f->l.p->numparams;
284         }
285         break;
286       }
287       case 't': {
288         ar->istailcall = (ci) ? ci->callstatus & CIST_TAIL : 0;
289         break;
290       }
291       case 'n': {
292         ar->namewhat = getfuncname(L, ci, &ar->name);
293         if (ar->namewhat == NULL) {
294           ar->namewhat = "";  /* not found */
295           ar->name = NULL;
296         }
297         break;
298       }
299       case 'L':
300       case 'f':  /* handled by lua_getinfo */
301         break;
302       default: status = 0;  /* invalid option */
303     }
304   }
305   return status;
306 }
307 
308 
309 LUA_API int lua_getinfo (lua_State *L, const char *what, lua_Debug *ar) {
310   int status;
311   Closure *cl;
312   CallInfo *ci;
313   StkId func;
314   lua_lock(L);
315   swapextra(L);
316   if (*what == '>') {
317     ci = NULL;
318     func = L->top - 1;
319     api_check(L, ttisfunction(func), "function expected");
320     what++;  /* skip the '>' */
321     L->top--;  /* pop function */
322   }
323   else {
324     ci = ar->i_ci;
325     func = ci->func;
326     lua_assert(ttisfunction(ci->func));
327   }
328   cl = ttisclosure(func) ? clvalue(func) : NULL;
329   status = auxgetinfo(L, what, ar, cl, ci);
330   if (strchr(what, 'f')) {
331     setobjs2s(L, L->top, func);
332     api_incr_top(L);
333   }
334   swapextra(L);  /* correct before option 'L', which can raise a mem. error */
335   if (strchr(what, 'L'))
336     collectvalidlines(L, cl);
337   lua_unlock(L);
338   return status;
339 }
340 
341 
342 /*
343 ** {======================================================
344 ** Symbolic Execution
345 ** =======================================================
346 */
347 
348 static const char *getobjname (Proto *p, int lastpc, int reg,
349                                const char **name);
350 
351 
352 /*
353 ** find a "name" for the RK value 'c'
354 */
355 static void kname (Proto *p, int pc, int c, const char **name) {
356   if (ISK(c)) {  /* is 'c' a constant? */
357     TValue *kvalue = &p->k[INDEXK(c)];
358     if (ttisstring(kvalue)) {  /* literal constant? */
359       *name = svalue(kvalue);  /* it is its own name */
360       return;
361     }
362     /* else no reasonable name found */
363   }
364   else {  /* 'c' is a register */
365     const char *what = getobjname(p, pc, c, name); /* search for 'c' */
366     if (what && *what == 'c') {  /* found a constant name? */
367       return;  /* 'name' already filled */
368     }
369     /* else no reasonable name found */
370   }
371   *name = "?";  /* no reasonable name found */
372 }
373 
374 
375 static int filterpc (int pc, int jmptarget) {
376   if (pc < jmptarget)  /* is code conditional (inside a jump)? */
377     return -1;  /* cannot know who sets that register */
378   else return pc;  /* current position sets that register */
379 }
380 
381 
382 /*
383 ** try to find last instruction before 'lastpc' that modified register 'reg'
384 */
385 static int findsetreg (Proto *p, int lastpc, int reg) {
386   int pc;
387   int setreg = -1;  /* keep last instruction that changed 'reg' */
388   int jmptarget = 0;  /* any code before this address is conditional */
389   for (pc = 0; pc < lastpc; pc++) {
390     Instruction i = p->code[pc];
391     OpCode op = GET_OPCODE(i);
392     int a = GETARG_A(i);
393     switch (op) {
394       case OP_LOADNIL: {
395         int b = GETARG_B(i);
396         if (a <= reg && reg <= a + b)  /* set registers from 'a' to 'a+b' */
397           setreg = filterpc(pc, jmptarget);
398         break;
399       }
400       case OP_TFORCALL: {
401         if (reg >= a + 2)  /* affect all regs above its base */
402           setreg = filterpc(pc, jmptarget);
403         break;
404       }
405       case OP_CALL:
406       case OP_TAILCALL: {
407         if (reg >= a)  /* affect all registers above base */
408           setreg = filterpc(pc, jmptarget);
409         break;
410       }
411       case OP_JMP: {
412         int b = GETARG_sBx(i);
413         int dest = pc + 1 + b;
414         /* jump is forward and do not skip 'lastpc'? */
415         if (pc < dest && dest <= lastpc) {
416           if (dest > jmptarget)
417             jmptarget = dest;  /* update 'jmptarget' */
418         }
419         break;
420       }
421       default:
422         if (testAMode(op) && reg == a)  /* any instruction that set A */
423           setreg = filterpc(pc, jmptarget);
424         break;
425     }
426   }
427   return setreg;
428 }
429 
430 
431 static const char *getobjname (Proto *p, int lastpc, int reg,
432                                const char **name) {
433   int pc;
434   *name = luaF_getlocalname(p, reg + 1, lastpc);
435   if (*name)  /* is a local? */
436     return "local";
437   /* else try symbolic execution */
438   pc = findsetreg(p, lastpc, reg);
439   if (pc != -1) {  /* could find instruction? */
440     Instruction i = p->code[pc];
441     OpCode op = GET_OPCODE(i);
442     switch (op) {
443       case OP_MOVE: {
444         int b = GETARG_B(i);  /* move from 'b' to 'a' */
445         if (b < GETARG_A(i))
446           return getobjname(p, pc, b, name);  /* get name for 'b' */
447         break;
448       }
449       case OP_GETTABUP:
450       case OP_GETTABLE: {
451         int k = GETARG_C(i);  /* key index */
452         int t = GETARG_B(i);  /* table index */
453         const char *vn = (op == OP_GETTABLE)  /* name of indexed variable */
454                          ? luaF_getlocalname(p, t + 1, pc)
455                          : upvalname(p, t);
456         kname(p, pc, k, name);
457         return (vn && strcmp(vn, LUA_ENV) == 0) ? "global" : "field";
458       }
459       case OP_GETUPVAL: {
460         *name = upvalname(p, GETARG_B(i));
461         return "upvalue";
462       }
463       case OP_LOADK:
464       case OP_LOADKX: {
465         int b = (op == OP_LOADK) ? GETARG_Bx(i)
466                                  : GETARG_Ax(p->code[pc + 1]);
467         if (ttisstring(&p->k[b])) {
468           *name = svalue(&p->k[b]);
469           return "constant";
470         }
471         break;
472       }
473       case OP_SELF: {
474         int k = GETARG_C(i);  /* key index */
475         kname(p, pc, k, name);
476         return "method";
477       }
478       default: break;  /* go through to return NULL */
479     }
480   }
481   return NULL;  /* could not find reasonable name */
482 }
483 
484 
485 /*
486 ** Try to find a name for a function based on the code that called it.
487 ** (Only works when function was called by a Lua function.)
488 ** Returns what the name is (e.g., "for iterator", "method",
489 ** "metamethod") and sets '*name' to point to the name.
490 */
491 static const char *funcnamefromcode (lua_State *L, CallInfo *ci,
492                                      const char **name) {
493   TMS tm = (TMS)0;  /* (initial value avoids warnings) */
494   Proto *p = ci_func(ci)->p;  /* calling function */
495   int pc = currentpc(ci);  /* calling instruction index */
496   Instruction i = p->code[pc];  /* calling instruction */
497   if (ci->callstatus & CIST_HOOKED) {  /* was it called inside a hook? */
498     *name = "?";
499     return "hook";
500   }
501   switch (GET_OPCODE(i)) {
502     case OP_CALL:
503     case OP_TAILCALL:
504       return getobjname(p, pc, GETARG_A(i), name);  /* get function name */
505     case OP_TFORCALL: {  /* for iterator */
506       *name = "for iterator";
507        return "for iterator";
508     }
509     /* other instructions can do calls through metamethods */
510     case OP_SELF: case OP_GETTABUP: case OP_GETTABLE:
511       tm = TM_INDEX;
512       break;
513     case OP_SETTABUP: case OP_SETTABLE:
514       tm = TM_NEWINDEX;
515       break;
516     case OP_ADD: case OP_SUB: case OP_MUL: case OP_MOD:
517     case OP_POW: case OP_DIV: case OP_IDIV: case OP_BAND:
518     case OP_BOR: case OP_BXOR: case OP_SHL: case OP_SHR: {
519       int offset = cast_int(GET_OPCODE(i)) - cast_int(OP_ADD);  /* ORDER OP */
520       tm = cast(TMS, offset + cast_int(TM_ADD));  /* ORDER TM */
521       break;
522     }
523     case OP_UNM: tm = TM_UNM; break;
524     case OP_BNOT: tm = TM_BNOT; break;
525     case OP_LEN: tm = TM_LEN; break;
526     case OP_CONCAT: tm = TM_CONCAT; break;
527     case OP_EQ: tm = TM_EQ; break;
528     case OP_LT: tm = TM_LT; break;
529     case OP_LE: tm = TM_LE; break;
530     default:
531       return NULL;  /* cannot find a reasonable name */
532   }
533   *name = getstr(G(L)->tmname[tm]);
534   return "metamethod";
535 }
536 
537 /* }====================================================== */
538 
539 
540 
541 /*
542 ** The subtraction of two potentially unrelated pointers is
543 ** not ISO C, but it should not crash a program; the subsequent
544 ** checks are ISO C and ensure a correct result.
545 */
546 static int isinstack (CallInfo *ci, const TValue *o) {
547   ptrdiff_t i = o - ci->u.l.base;
548   return (0 <= i && i < (ci->top - ci->u.l.base) && ci->u.l.base + i == o);
549 }
550 
551 
552 /*
553 ** Checks whether value 'o' came from an upvalue. (That can only happen
554 ** with instructions OP_GETTABUP/OP_SETTABUP, which operate directly on
555 ** upvalues.)
556 */
557 static const char *getupvalname (CallInfo *ci, const TValue *o,
558                                  const char **name) {
559   LClosure *c = ci_func(ci);
560   int i;
561   for (i = 0; i < c->nupvalues; i++) {
562     if (c->upvals[i]->v == o) {
563       *name = upvalname(c->p, i);
564       return "upvalue";
565     }
566   }
567   return NULL;
568 }
569 
570 
571 static const char *varinfo (lua_State *L, const TValue *o) {
572   const char *name = NULL;  /* to avoid warnings */
573   CallInfo *ci = L->ci;
574   const char *kind = NULL;
575   if (isLua(ci)) {
576     kind = getupvalname(ci, o, &name);  /* check whether 'o' is an upvalue */
577     if (!kind && isinstack(ci, o))  /* no? try a register */
578       kind = getobjname(ci_func(ci)->p, currentpc(ci),
579                         cast_int(o - ci->u.l.base), &name);
580   }
581   return (kind) ? luaO_pushfstring(L, " (%s '%s')", kind, name) : "";
582 }
583 
584 
585 l_noret luaG_typeerror (lua_State *L, const TValue *o, const char *op) {
586   const char *t = luaT_objtypename(L, o);
587   luaG_runerror(L, "attempt to %s a %s value%s", op, t, varinfo(L, o));
588 }
589 
590 
591 l_noret luaG_concaterror (lua_State *L, const TValue *p1, const TValue *p2) {
592   if (ttisstring(p1) || cvt2str(p1)) p1 = p2;
593   luaG_typeerror(L, p1, "concatenate");
594 }
595 
596 
597 l_noret luaG_opinterror (lua_State *L, const TValue *p1,
598                          const TValue *p2, const char *msg) {
599   lua_Number temp;
600   if (!tonumber(p1, &temp))  /* first operand is wrong? */
601     p2 = p1;  /* now second is wrong */
602   luaG_typeerror(L, p2, msg);
603 }
604 
605 
606 /*
607 ** Error when both values are convertible to numbers, but not to integers
608 */
609 l_noret luaG_tointerror (lua_State *L, const TValue *p1, const TValue *p2) {
610   lua_Integer temp;
611   if (!tointeger(p1, &temp))
612     p2 = p1;
613   luaG_runerror(L, "number%s has no integer representation", varinfo(L, p2));
614 }
615 
616 
617 l_noret luaG_ordererror (lua_State *L, const TValue *p1, const TValue *p2) {
618   const char *t1 = luaT_objtypename(L, p1);
619   const char *t2 = luaT_objtypename(L, p2);
620   if (strcmp(t1, t2) == 0)
621     luaG_runerror(L, "attempt to compare two %s values", t1);
622   else
623     luaG_runerror(L, "attempt to compare %s with %s", t1, t2);
624 }
625 
626 
627 /* add src:line information to 'msg' */
628 const char *luaG_addinfo (lua_State *L, const char *msg, TString *src,
629                                         int line) {
630   char buff[LUA_IDSIZE];
631   if (src)
632     luaO_chunkid(buff, getstr(src), LUA_IDSIZE);
633   else {  /* no source available; use "?" instead */
634     buff[0] = '?'; buff[1] = '\0';
635   }
636   return luaO_pushfstring(L, "%s:%d: %s", buff, line, msg);
637 }
638 
639 
640 l_noret luaG_errormsg (lua_State *L) {
641   if (L->errfunc != 0) {  /* is there an error handling function? */
642     StkId errfunc = restorestack(L, L->errfunc);
643     setobjs2s(L, L->top, L->top - 1);  /* move argument */
644     setobjs2s(L, L->top - 1, errfunc);  /* push function */
645     L->top++;  /* assume EXTRA_STACK */
646     luaD_callnoyield(L, L->top - 2, 1);  /* call it */
647   }
648   luaD_throw(L, LUA_ERRRUN);
649 }
650 
651 
652 l_noret luaG_runerror (lua_State *L, const char *fmt, ...) {
653   CallInfo *ci = L->ci;
654   const char *msg;
655   va_list argp;
656   va_start(argp, fmt);
657   msg = luaO_pushvfstring(L, fmt, argp);  /* format message */
658   va_end(argp);
659   if (isLua(ci))  /* if Lua function, add source:line information */
660     luaG_addinfo(L, msg, ci_func(ci)->p->source, currentline(ci));
661   luaG_errormsg(L);
662 }
663 
664 
665 void luaG_traceexec (lua_State *L) {
666   CallInfo *ci = L->ci;
667   lu_byte mask = L->hookmask;
668   int counthook = (--L->hookcount == 0 && (mask & LUA_MASKCOUNT));
669   if (counthook)
670     resethookcount(L);  /* reset count */
671   else if (!(mask & LUA_MASKLINE))
672     return;  /* no line hook and count != 0; nothing to be done */
673   if (ci->callstatus & CIST_HOOKYIELD) {  /* called hook last time? */
674     ci->callstatus &= ~CIST_HOOKYIELD;  /* erase mark */
675     return;  /* do not call hook again (VM yielded, so it did not move) */
676   }
677   if (counthook)
678     luaD_hook(L, LUA_HOOKCOUNT, -1);  /* call count hook */
679   if (mask & LUA_MASKLINE) {
680     Proto *p = ci_func(ci)->p;
681     int npc = pcRel(ci->u.l.savedpc, p);
682     int newline = getfuncline(p, npc);
683     if (npc == 0 ||  /* call linehook when enter a new function, */
684         ci->u.l.savedpc <= L->oldpc ||  /* when jump back (loop), or when */
685         newline != getfuncline(p, pcRel(L->oldpc, p)))  /* enter a new line */
686       luaD_hook(L, LUA_HOOKLINE, newline);  /* call line hook */
687   }
688   L->oldpc = ci->u.l.savedpc;
689   if (L->status == LUA_YIELD) {  /* did hook yield? */
690     if (counthook)
691       L->hookcount = 1;  /* undo decrement to zero */
692     ci->u.l.savedpc--;  /* undo increment (resume will increment it again) */
693     ci->callstatus |= CIST_HOOKYIELD;  /* mark that it yielded */
694     ci->func = L->top - 1;  /* protect stack below results */
695     luaD_throw(L, LUA_YIELD);
696   }
697 }
698 
699