Merge tag 'trace-v4.19-rc8-3' of git://git.kernel.org/pub/scm/linux/kernel/git/rosted...
[muen/linux.git] / kernel / trace / trace_probe.c
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Common code for probe-based Dynamic events.
4  *
5  * This code was copied from kernel/trace/trace_kprobe.c written by
6  * Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
7  *
8  * Updates to make this generic:
9  * Copyright (C) IBM Corporation, 2010-2011
10  * Author:     Srikar Dronamraju
11  */
12 #define pr_fmt(fmt)     "trace_probe: " fmt
13
14 #include "trace_probe.h"
15
16 const char *reserved_field_names[] = {
17         "common_type",
18         "common_flags",
19         "common_preempt_count",
20         "common_pid",
21         "common_tgid",
22         FIELD_STRING_IP,
23         FIELD_STRING_RETIP,
24         FIELD_STRING_FUNC,
25 };
26
27 /* Printing  in basic type function template */
28 #define DEFINE_BASIC_PRINT_TYPE_FUNC(tname, type, fmt)                  \
29 int PRINT_TYPE_FUNC_NAME(tname)(struct trace_seq *s, const char *name,  \
30                                 void *data, void *ent)                  \
31 {                                                                       \
32         trace_seq_printf(s, " %s=" fmt, name, *(type *)data);           \
33         return !trace_seq_has_overflowed(s);                            \
34 }                                                                       \
35 const char PRINT_TYPE_FMT_NAME(tname)[] = fmt;                          \
36 NOKPROBE_SYMBOL(PRINT_TYPE_FUNC_NAME(tname));
37
38 DEFINE_BASIC_PRINT_TYPE_FUNC(u8,  u8,  "%u")
39 DEFINE_BASIC_PRINT_TYPE_FUNC(u16, u16, "%u")
40 DEFINE_BASIC_PRINT_TYPE_FUNC(u32, u32, "%u")
41 DEFINE_BASIC_PRINT_TYPE_FUNC(u64, u64, "%Lu")
42 DEFINE_BASIC_PRINT_TYPE_FUNC(s8,  s8,  "%d")
43 DEFINE_BASIC_PRINT_TYPE_FUNC(s16, s16, "%d")
44 DEFINE_BASIC_PRINT_TYPE_FUNC(s32, s32, "%d")
45 DEFINE_BASIC_PRINT_TYPE_FUNC(s64, s64, "%Ld")
46 DEFINE_BASIC_PRINT_TYPE_FUNC(x8,  u8,  "0x%x")
47 DEFINE_BASIC_PRINT_TYPE_FUNC(x16, u16, "0x%x")
48 DEFINE_BASIC_PRINT_TYPE_FUNC(x32, u32, "0x%x")
49 DEFINE_BASIC_PRINT_TYPE_FUNC(x64, u64, "0x%Lx")
50
51 /* Print type function for string type */
52 int PRINT_TYPE_FUNC_NAME(string)(struct trace_seq *s, const char *name,
53                                  void *data, void *ent)
54 {
55         int len = *(u32 *)data >> 16;
56
57         if (!len)
58                 trace_seq_printf(s, " %s=(fault)", name);
59         else
60                 trace_seq_printf(s, " %s=\"%s\"", name,
61                                  (const char *)get_loc_data(data, ent));
62         return !trace_seq_has_overflowed(s);
63 }
64 NOKPROBE_SYMBOL(PRINT_TYPE_FUNC_NAME(string));
65
66 const char PRINT_TYPE_FMT_NAME(string)[] = "\\\"%s\\\"";
67
68 #define CHECK_FETCH_FUNCS(method, fn)                   \
69         (((FETCH_FUNC_NAME(method, u8) == fn) ||        \
70           (FETCH_FUNC_NAME(method, u16) == fn) ||       \
71           (FETCH_FUNC_NAME(method, u32) == fn) ||       \
72           (FETCH_FUNC_NAME(method, u64) == fn) ||       \
73           (FETCH_FUNC_NAME(method, string) == fn) ||    \
74           (FETCH_FUNC_NAME(method, string_size) == fn)) \
75          && (fn != NULL))
76
77 /* Data fetch function templates */
78 #define DEFINE_FETCH_reg(type)                                          \
79 void FETCH_FUNC_NAME(reg, type)(struct pt_regs *regs, void *offset, void *dest) \
80 {                                                                       \
81         *(type *)dest = (type)regs_get_register(regs,                   \
82                                 (unsigned int)((unsigned long)offset)); \
83 }                                                                       \
84 NOKPROBE_SYMBOL(FETCH_FUNC_NAME(reg, type));
85 DEFINE_BASIC_FETCH_FUNCS(reg)
86 /* No string on the register */
87 #define fetch_reg_string        NULL
88 #define fetch_reg_string_size   NULL
89
90 #define DEFINE_FETCH_retval(type)                                       \
91 void FETCH_FUNC_NAME(retval, type)(struct pt_regs *regs,                \
92                                    void *dummy, void *dest)             \
93 {                                                                       \
94         *(type *)dest = (type)regs_return_value(regs);                  \
95 }                                                                       \
96 NOKPROBE_SYMBOL(FETCH_FUNC_NAME(retval, type));
97 DEFINE_BASIC_FETCH_FUNCS(retval)
98 /* No string on the retval */
99 #define fetch_retval_string             NULL
100 #define fetch_retval_string_size        NULL
101
102 /* Dereference memory access function */
103 struct deref_fetch_param {
104         struct fetch_param      orig;
105         long                    offset;
106         fetch_func_t            fetch;
107         fetch_func_t            fetch_size;
108 };
109
110 #define DEFINE_FETCH_deref(type)                                        \
111 void FETCH_FUNC_NAME(deref, type)(struct pt_regs *regs,                 \
112                                   void *data, void *dest)               \
113 {                                                                       \
114         struct deref_fetch_param *dprm = data;                          \
115         unsigned long addr;                                             \
116         call_fetch(&dprm->orig, regs, &addr);                           \
117         if (addr) {                                                     \
118                 addr += dprm->offset;                                   \
119                 dprm->fetch(regs, (void *)addr, dest);                  \
120         } else                                                          \
121                 *(type *)dest = 0;                                      \
122 }                                                                       \
123 NOKPROBE_SYMBOL(FETCH_FUNC_NAME(deref, type));
124 DEFINE_BASIC_FETCH_FUNCS(deref)
125 DEFINE_FETCH_deref(string)
126
127 void FETCH_FUNC_NAME(deref, string_size)(struct pt_regs *regs,
128                                          void *data, void *dest)
129 {
130         struct deref_fetch_param *dprm = data;
131         unsigned long addr;
132
133         call_fetch(&dprm->orig, regs, &addr);
134         if (addr && dprm->fetch_size) {
135                 addr += dprm->offset;
136                 dprm->fetch_size(regs, (void *)addr, dest);
137         } else
138                 *(string_size *)dest = 0;
139 }
140 NOKPROBE_SYMBOL(FETCH_FUNC_NAME(deref, string_size));
141
142 static void update_deref_fetch_param(struct deref_fetch_param *data)
143 {
144         if (CHECK_FETCH_FUNCS(deref, data->orig.fn))
145                 update_deref_fetch_param(data->orig.data);
146         else if (CHECK_FETCH_FUNCS(symbol, data->orig.fn))
147                 update_symbol_cache(data->orig.data);
148 }
149 NOKPROBE_SYMBOL(update_deref_fetch_param);
150
151 static void free_deref_fetch_param(struct deref_fetch_param *data)
152 {
153         if (CHECK_FETCH_FUNCS(deref, data->orig.fn))
154                 free_deref_fetch_param(data->orig.data);
155         else if (CHECK_FETCH_FUNCS(symbol, data->orig.fn))
156                 free_symbol_cache(data->orig.data);
157         kfree(data);
158 }
159 NOKPROBE_SYMBOL(free_deref_fetch_param);
160
161 /* Bitfield fetch function */
162 struct bitfield_fetch_param {
163         struct fetch_param      orig;
164         unsigned char           hi_shift;
165         unsigned char           low_shift;
166 };
167
168 #define DEFINE_FETCH_bitfield(type)                                     \
169 void FETCH_FUNC_NAME(bitfield, type)(struct pt_regs *regs,              \
170                                      void *data, void *dest)            \
171 {                                                                       \
172         struct bitfield_fetch_param *bprm = data;                       \
173         type buf = 0;                                                   \
174         call_fetch(&bprm->orig, regs, &buf);                            \
175         if (buf) {                                                      \
176                 buf <<= bprm->hi_shift;                                 \
177                 buf >>= bprm->low_shift;                                \
178         }                                                               \
179         *(type *)dest = buf;                                            \
180 }                                                                       \
181 NOKPROBE_SYMBOL(FETCH_FUNC_NAME(bitfield, type));
182 DEFINE_BASIC_FETCH_FUNCS(bitfield)
183 #define fetch_bitfield_string           NULL
184 #define fetch_bitfield_string_size      NULL
185
186 static void
187 update_bitfield_fetch_param(struct bitfield_fetch_param *data)
188 {
189         /*
190          * Don't check the bitfield itself, because this must be the
191          * last fetch function.
192          */
193         if (CHECK_FETCH_FUNCS(deref, data->orig.fn))
194                 update_deref_fetch_param(data->orig.data);
195         else if (CHECK_FETCH_FUNCS(symbol, data->orig.fn))
196                 update_symbol_cache(data->orig.data);
197 }
198
199 static void
200 free_bitfield_fetch_param(struct bitfield_fetch_param *data)
201 {
202         /*
203          * Don't check the bitfield itself, because this must be the
204          * last fetch function.
205          */
206         if (CHECK_FETCH_FUNCS(deref, data->orig.fn))
207                 free_deref_fetch_param(data->orig.data);
208         else if (CHECK_FETCH_FUNCS(symbol, data->orig.fn))
209                 free_symbol_cache(data->orig.data);
210
211         kfree(data);
212 }
213
214 void FETCH_FUNC_NAME(comm, string)(struct pt_regs *regs,
215                                           void *data, void *dest)
216 {
217         int maxlen = get_rloc_len(*(u32 *)dest);
218         u8 *dst = get_rloc_data(dest);
219         long ret;
220
221         if (!maxlen)
222                 return;
223
224         ret = strlcpy(dst, current->comm, maxlen);
225         *(u32 *)dest = make_data_rloc(ret, get_rloc_offs(*(u32 *)dest));
226 }
227 NOKPROBE_SYMBOL(FETCH_FUNC_NAME(comm, string));
228
229 void FETCH_FUNC_NAME(comm, string_size)(struct pt_regs *regs,
230                                                void *data, void *dest)
231 {
232         *(u32 *)dest = strlen(current->comm) + 1;
233 }
234 NOKPROBE_SYMBOL(FETCH_FUNC_NAME(comm, string_size));
235
236 static const struct fetch_type *find_fetch_type(const char *type,
237                                                 const struct fetch_type *ftbl)
238 {
239         int i;
240
241         if (!type)
242                 type = DEFAULT_FETCH_TYPE_STR;
243
244         /* Special case: bitfield */
245         if (*type == 'b') {
246                 unsigned long bs;
247
248                 type = strchr(type, '/');
249                 if (!type)
250                         goto fail;
251
252                 type++;
253                 if (kstrtoul(type, 0, &bs))
254                         goto fail;
255
256                 switch (bs) {
257                 case 8:
258                         return find_fetch_type("u8", ftbl);
259                 case 16:
260                         return find_fetch_type("u16", ftbl);
261                 case 32:
262                         return find_fetch_type("u32", ftbl);
263                 case 64:
264                         return find_fetch_type("u64", ftbl);
265                 default:
266                         goto fail;
267                 }
268         }
269
270         for (i = 0; ftbl[i].name; i++) {
271                 if (strcmp(type, ftbl[i].name) == 0)
272                         return &ftbl[i];
273         }
274
275 fail:
276         return NULL;
277 }
278
279 /* Special function : only accept unsigned long */
280 static void fetch_kernel_stack_address(struct pt_regs *regs, void *dummy, void *dest)
281 {
282         *(unsigned long *)dest = kernel_stack_pointer(regs);
283 }
284 NOKPROBE_SYMBOL(fetch_kernel_stack_address);
285
286 static void fetch_user_stack_address(struct pt_regs *regs, void *dummy, void *dest)
287 {
288         *(unsigned long *)dest = user_stack_pointer(regs);
289 }
290 NOKPROBE_SYMBOL(fetch_user_stack_address);
291
292 static fetch_func_t get_fetch_size_function(const struct fetch_type *type,
293                                             fetch_func_t orig_fn,
294                                             const struct fetch_type *ftbl)
295 {
296         int i;
297
298         if (type != &ftbl[FETCH_TYPE_STRING])
299                 return NULL;    /* Only string type needs size function */
300
301         for (i = 0; i < FETCH_MTD_END; i++)
302                 if (type->fetch[i] == orig_fn)
303                         return ftbl[FETCH_TYPE_STRSIZE].fetch[i];
304
305         WARN_ON(1);     /* This should not happen */
306
307         return NULL;
308 }
309
310 /* Split symbol and offset. */
311 int traceprobe_split_symbol_offset(char *symbol, long *offset)
312 {
313         char *tmp;
314         int ret;
315
316         if (!offset)
317                 return -EINVAL;
318
319         tmp = strpbrk(symbol, "+-");
320         if (tmp) {
321                 ret = kstrtol(tmp, 0, offset);
322                 if (ret)
323                         return ret;
324                 *tmp = '\0';
325         } else
326                 *offset = 0;
327
328         return 0;
329 }
330
331 #define PARAM_MAX_STACK (THREAD_SIZE / sizeof(unsigned long))
332
333 static int parse_probe_vars(char *arg, const struct fetch_type *t,
334                             struct fetch_param *f, bool is_return,
335                             bool is_kprobe)
336 {
337         int ret = 0;
338         unsigned long param;
339
340         if (strcmp(arg, "retval") == 0) {
341                 if (is_return)
342                         f->fn = t->fetch[FETCH_MTD_retval];
343                 else
344                         ret = -EINVAL;
345         } else if (strncmp(arg, "stack", 5) == 0) {
346                 if (arg[5] == '\0') {
347                         if (strcmp(t->name, DEFAULT_FETCH_TYPE_STR))
348                                 return -EINVAL;
349
350                         if (is_kprobe)
351                                 f->fn = fetch_kernel_stack_address;
352                         else
353                                 f->fn = fetch_user_stack_address;
354                 } else if (isdigit(arg[5])) {
355                         ret = kstrtoul(arg + 5, 10, &param);
356                         if (ret || (is_kprobe && param > PARAM_MAX_STACK))
357                                 ret = -EINVAL;
358                         else {
359                                 f->fn = t->fetch[FETCH_MTD_stack];
360                                 f->data = (void *)param;
361                         }
362                 } else
363                         ret = -EINVAL;
364         } else if (strcmp(arg, "comm") == 0) {
365                 if (strcmp(t->name, "string") != 0 &&
366                     strcmp(t->name, "string_size") != 0)
367                         return -EINVAL;
368                 f->fn = t->fetch[FETCH_MTD_comm];
369         } else
370                 ret = -EINVAL;
371
372         return ret;
373 }
374
375 /* Recursive argument parser */
376 static int parse_probe_arg(char *arg, const struct fetch_type *t,
377                      struct fetch_param *f, bool is_return, bool is_kprobe,
378                      const struct fetch_type *ftbl)
379 {
380         unsigned long param;
381         long offset;
382         char *tmp;
383         int ret = 0;
384
385         switch (arg[0]) {
386         case '$':
387                 ret = parse_probe_vars(arg + 1, t, f, is_return, is_kprobe);
388                 break;
389
390         case '%':       /* named register */
391                 ret = regs_query_register_offset(arg + 1);
392                 if (ret >= 0) {
393                         f->fn = t->fetch[FETCH_MTD_reg];
394                         f->data = (void *)(unsigned long)ret;
395                         ret = 0;
396                 }
397                 break;
398
399         case '@':       /* memory, file-offset or symbol */
400                 if (isdigit(arg[1])) {
401                         ret = kstrtoul(arg + 1, 0, &param);
402                         if (ret)
403                                 break;
404
405                         f->fn = t->fetch[FETCH_MTD_memory];
406                         f->data = (void *)param;
407                 } else if (arg[1] == '+') {
408                         /* kprobes don't support file offsets */
409                         if (is_kprobe)
410                                 return -EINVAL;
411
412                         ret = kstrtol(arg + 2, 0, &offset);
413                         if (ret)
414                                 break;
415
416                         f->fn = t->fetch[FETCH_MTD_file_offset];
417                         f->data = (void *)offset;
418                 } else {
419                         /* uprobes don't support symbols */
420                         if (!is_kprobe)
421                                 return -EINVAL;
422
423                         ret = traceprobe_split_symbol_offset(arg + 1, &offset);
424                         if (ret)
425                                 break;
426
427                         f->data = alloc_symbol_cache(arg + 1, offset);
428                         if (f->data)
429                                 f->fn = t->fetch[FETCH_MTD_symbol];
430                 }
431                 break;
432
433         case '+':       /* deref memory */
434                 arg++;  /* Skip '+', because kstrtol() rejects it. */
435         case '-':
436                 tmp = strchr(arg, '(');
437                 if (!tmp)
438                         break;
439
440                 *tmp = '\0';
441                 ret = kstrtol(arg, 0, &offset);
442
443                 if (ret)
444                         break;
445
446                 arg = tmp + 1;
447                 tmp = strrchr(arg, ')');
448
449                 if (tmp) {
450                         struct deref_fetch_param        *dprm;
451                         const struct fetch_type         *t2;
452
453                         t2 = find_fetch_type(NULL, ftbl);
454                         *tmp = '\0';
455                         dprm = kzalloc(sizeof(struct deref_fetch_param), GFP_KERNEL);
456
457                         if (!dprm)
458                                 return -ENOMEM;
459
460                         dprm->offset = offset;
461                         dprm->fetch = t->fetch[FETCH_MTD_memory];
462                         dprm->fetch_size = get_fetch_size_function(t,
463                                                         dprm->fetch, ftbl);
464                         ret = parse_probe_arg(arg, t2, &dprm->orig, is_return,
465                                                         is_kprobe, ftbl);
466                         if (ret)
467                                 kfree(dprm);
468                         else {
469                                 f->fn = t->fetch[FETCH_MTD_deref];
470                                 f->data = (void *)dprm;
471                         }
472                 }
473                 break;
474         }
475         if (!ret && !f->fn) {   /* Parsed, but do not find fetch method */
476                 pr_info("%s type has no corresponding fetch method.\n", t->name);
477                 ret = -EINVAL;
478         }
479
480         return ret;
481 }
482
483 #define BYTES_TO_BITS(nb)       ((BITS_PER_LONG * (nb)) / sizeof(long))
484
485 /* Bitfield type needs to be parsed into a fetch function */
486 static int __parse_bitfield_probe_arg(const char *bf,
487                                       const struct fetch_type *t,
488                                       struct fetch_param *f)
489 {
490         struct bitfield_fetch_param *bprm;
491         unsigned long bw, bo;
492         char *tail;
493
494         if (*bf != 'b')
495                 return 0;
496
497         bprm = kzalloc(sizeof(*bprm), GFP_KERNEL);
498         if (!bprm)
499                 return -ENOMEM;
500
501         bprm->orig = *f;
502         f->fn = t->fetch[FETCH_MTD_bitfield];
503         f->data = (void *)bprm;
504         bw = simple_strtoul(bf + 1, &tail, 0);  /* Use simple one */
505
506         if (bw == 0 || *tail != '@')
507                 return -EINVAL;
508
509         bf = tail + 1;
510         bo = simple_strtoul(bf, &tail, 0);
511
512         if (tail == bf || *tail != '/')
513                 return -EINVAL;
514
515         bprm->hi_shift = BYTES_TO_BITS(t->size) - (bw + bo);
516         bprm->low_shift = bprm->hi_shift + bo;
517
518         return (BYTES_TO_BITS(t->size) < (bw + bo)) ? -EINVAL : 0;
519 }
520
521 /* String length checking wrapper */
522 int traceprobe_parse_probe_arg(char *arg, ssize_t *size,
523                 struct probe_arg *parg, bool is_return, bool is_kprobe,
524                 const struct fetch_type *ftbl)
525 {
526         const char *t;
527         int ret;
528
529         if (strlen(arg) > MAX_ARGSTR_LEN) {
530                 pr_info("Argument is too long.: %s\n",  arg);
531                 return -ENOSPC;
532         }
533         parg->comm = kstrdup(arg, GFP_KERNEL);
534         if (!parg->comm) {
535                 pr_info("Failed to allocate memory for command '%s'.\n", arg);
536                 return -ENOMEM;
537         }
538         t = strchr(parg->comm, ':');
539         if (t) {
540                 arg[t - parg->comm] = '\0';
541                 t++;
542         }
543         /*
544          * The default type of $comm should be "string", and it can't be
545          * dereferenced.
546          */
547         if (!t && strcmp(arg, "$comm") == 0)
548                 t = "string";
549         parg->type = find_fetch_type(t, ftbl);
550         if (!parg->type) {
551                 pr_info("Unsupported type: %s\n", t);
552                 return -EINVAL;
553         }
554         parg->offset = *size;
555         *size += parg->type->size;
556         ret = parse_probe_arg(arg, parg->type, &parg->fetch, is_return,
557                               is_kprobe, ftbl);
558
559         if (ret >= 0 && t != NULL)
560                 ret = __parse_bitfield_probe_arg(t, parg->type, &parg->fetch);
561
562         if (ret >= 0) {
563                 parg->fetch_size.fn = get_fetch_size_function(parg->type,
564                                                               parg->fetch.fn,
565                                                               ftbl);
566                 parg->fetch_size.data = parg->fetch.data;
567         }
568
569         return ret;
570 }
571
572 /* Return 1 if name is reserved or already used by another argument */
573 int traceprobe_conflict_field_name(const char *name,
574                                struct probe_arg *args, int narg)
575 {
576         int i;
577
578         for (i = 0; i < ARRAY_SIZE(reserved_field_names); i++)
579                 if (strcmp(reserved_field_names[i], name) == 0)
580                         return 1;
581
582         for (i = 0; i < narg; i++)
583                 if (strcmp(args[i].name, name) == 0)
584                         return 1;
585
586         return 0;
587 }
588
589 void traceprobe_update_arg(struct probe_arg *arg)
590 {
591         if (CHECK_FETCH_FUNCS(bitfield, arg->fetch.fn))
592                 update_bitfield_fetch_param(arg->fetch.data);
593         else if (CHECK_FETCH_FUNCS(deref, arg->fetch.fn))
594                 update_deref_fetch_param(arg->fetch.data);
595         else if (CHECK_FETCH_FUNCS(symbol, arg->fetch.fn))
596                 update_symbol_cache(arg->fetch.data);
597 }
598
599 void traceprobe_free_probe_arg(struct probe_arg *arg)
600 {
601         if (CHECK_FETCH_FUNCS(bitfield, arg->fetch.fn))
602                 free_bitfield_fetch_param(arg->fetch.data);
603         else if (CHECK_FETCH_FUNCS(deref, arg->fetch.fn))
604                 free_deref_fetch_param(arg->fetch.data);
605         else if (CHECK_FETCH_FUNCS(symbol, arg->fetch.fn))
606                 free_symbol_cache(arg->fetch.data);
607
608         kfree(arg->name);
609         kfree(arg->comm);
610 }
611
612 static int __set_print_fmt(struct trace_probe *tp, char *buf, int len,
613                            bool is_return)
614 {
615         int i;
616         int pos = 0;
617
618         const char *fmt, *arg;
619
620         if (!is_return) {
621                 fmt = "(%lx)";
622                 arg = "REC->" FIELD_STRING_IP;
623         } else {
624                 fmt = "(%lx <- %lx)";
625                 arg = "REC->" FIELD_STRING_FUNC ", REC->" FIELD_STRING_RETIP;
626         }
627
628         /* When len=0, we just calculate the needed length */
629 #define LEN_OR_ZERO (len ? len - pos : 0)
630
631         pos += snprintf(buf + pos, LEN_OR_ZERO, "\"%s", fmt);
632
633         for (i = 0; i < tp->nr_args; i++) {
634                 pos += snprintf(buf + pos, LEN_OR_ZERO, " %s=%s",
635                                 tp->args[i].name, tp->args[i].type->fmt);
636         }
637
638         pos += snprintf(buf + pos, LEN_OR_ZERO, "\", %s", arg);
639
640         for (i = 0; i < tp->nr_args; i++) {
641                 if (strcmp(tp->args[i].type->name, "string") == 0)
642                         pos += snprintf(buf + pos, LEN_OR_ZERO,
643                                         ", __get_str(%s)",
644                                         tp->args[i].name);
645                 else
646                         pos += snprintf(buf + pos, LEN_OR_ZERO, ", REC->%s",
647                                         tp->args[i].name);
648         }
649
650 #undef LEN_OR_ZERO
651
652         /* return the length of print_fmt */
653         return pos;
654 }
655
656 int set_print_fmt(struct trace_probe *tp, bool is_return)
657 {
658         int len;
659         char *print_fmt;
660
661         /* First: called with 0 length to calculate the needed length */
662         len = __set_print_fmt(tp, NULL, 0, is_return);
663         print_fmt = kmalloc(len + 1, GFP_KERNEL);
664         if (!print_fmt)
665                 return -ENOMEM;
666
667         /* Second: actually write the @print_fmt */
668         __set_print_fmt(tp, print_fmt, len + 1, is_return);
669         tp->call.print_fmt = print_fmt;
670
671         return 0;
672 }