Add the rt linux 4.1.3-rt3 as base
[kvmfornfv.git] / kernel / kernel / trace / trace_probe.c
diff --git a/kernel/kernel/trace/trace_probe.c b/kernel/kernel/trace/trace_probe.c
new file mode 100644 (file)
index 0000000..1769a81
--- /dev/null
@@ -0,0 +1,723 @@
+/*
+ * Common code for probe-based Dynamic events.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ * This code was copied from kernel/trace/trace_kprobe.c written by
+ * Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
+ *
+ * Updates to make this generic:
+ * Copyright (C) IBM Corporation, 2010-2011
+ * Author:     Srikar Dronamraju
+ */
+
+#include "trace_probe.h"
+
+const char *reserved_field_names[] = {
+       "common_type",
+       "common_flags",
+       "common_preempt_count",
+       "common_pid",
+       "common_tgid",
+       FIELD_STRING_IP,
+       FIELD_STRING_RETIP,
+       FIELD_STRING_FUNC,
+};
+
+/* Printing  in basic type function template */
+#define DEFINE_BASIC_PRINT_TYPE_FUNC(type, fmt)                                \
+int PRINT_TYPE_FUNC_NAME(type)(struct trace_seq *s, const char *name,  \
+                               void *data, void *ent)                  \
+{                                                                      \
+       trace_seq_printf(s, " %s=" fmt, name, *(type *)data);           \
+       return !trace_seq_has_overflowed(s);                            \
+}                                                                      \
+const char PRINT_TYPE_FMT_NAME(type)[] = fmt;                          \
+NOKPROBE_SYMBOL(PRINT_TYPE_FUNC_NAME(type));
+
+DEFINE_BASIC_PRINT_TYPE_FUNC(u8 , "0x%x")
+DEFINE_BASIC_PRINT_TYPE_FUNC(u16, "0x%x")
+DEFINE_BASIC_PRINT_TYPE_FUNC(u32, "0x%x")
+DEFINE_BASIC_PRINT_TYPE_FUNC(u64, "0x%Lx")
+DEFINE_BASIC_PRINT_TYPE_FUNC(s8,  "%d")
+DEFINE_BASIC_PRINT_TYPE_FUNC(s16, "%d")
+DEFINE_BASIC_PRINT_TYPE_FUNC(s32, "%d")
+DEFINE_BASIC_PRINT_TYPE_FUNC(s64, "%Ld")
+
+/* Print type function for string type */
+int PRINT_TYPE_FUNC_NAME(string)(struct trace_seq *s, const char *name,
+                                void *data, void *ent)
+{
+       int len = *(u32 *)data >> 16;
+
+       if (!len)
+               trace_seq_printf(s, " %s=(fault)", name);
+       else
+               trace_seq_printf(s, " %s=\"%s\"", name,
+                                (const char *)get_loc_data(data, ent));
+       return !trace_seq_has_overflowed(s);
+}
+NOKPROBE_SYMBOL(PRINT_TYPE_FUNC_NAME(string));
+
+const char PRINT_TYPE_FMT_NAME(string)[] = "\\\"%s\\\"";
+
+#define CHECK_FETCH_FUNCS(method, fn)                  \
+       (((FETCH_FUNC_NAME(method, u8) == fn) ||        \
+         (FETCH_FUNC_NAME(method, u16) == fn) ||       \
+         (FETCH_FUNC_NAME(method, u32) == fn) ||       \
+         (FETCH_FUNC_NAME(method, u64) == fn) ||       \
+         (FETCH_FUNC_NAME(method, string) == fn) ||    \
+         (FETCH_FUNC_NAME(method, string_size) == fn)) \
+        && (fn != NULL))
+
+/* Data fetch function templates */
+#define DEFINE_FETCH_reg(type)                                         \
+void FETCH_FUNC_NAME(reg, type)(struct pt_regs *regs, void *offset, void *dest)        \
+{                                                                      \
+       *(type *)dest = (type)regs_get_register(regs,                   \
+                               (unsigned int)((unsigned long)offset)); \
+}                                                                      \
+NOKPROBE_SYMBOL(FETCH_FUNC_NAME(reg, type));
+DEFINE_BASIC_FETCH_FUNCS(reg)
+/* No string on the register */
+#define fetch_reg_string       NULL
+#define fetch_reg_string_size  NULL
+
+#define DEFINE_FETCH_retval(type)                                      \
+void FETCH_FUNC_NAME(retval, type)(struct pt_regs *regs,               \
+                                  void *dummy, void *dest)             \
+{                                                                      \
+       *(type *)dest = (type)regs_return_value(regs);                  \
+}                                                                      \
+NOKPROBE_SYMBOL(FETCH_FUNC_NAME(retval, type));
+DEFINE_BASIC_FETCH_FUNCS(retval)
+/* No string on the retval */
+#define fetch_retval_string            NULL
+#define fetch_retval_string_size       NULL
+
+/* Dereference memory access function */
+struct deref_fetch_param {
+       struct fetch_param      orig;
+       long                    offset;
+       fetch_func_t            fetch;
+       fetch_func_t            fetch_size;
+};
+
+#define DEFINE_FETCH_deref(type)                                       \
+void FETCH_FUNC_NAME(deref, type)(struct pt_regs *regs,                        \
+                                 void *data, void *dest)               \
+{                                                                      \
+       struct deref_fetch_param *dprm = data;                          \
+       unsigned long addr;                                             \
+       call_fetch(&dprm->orig, regs, &addr);                           \
+       if (addr) {                                                     \
+               addr += dprm->offset;                                   \
+               dprm->fetch(regs, (void *)addr, dest);                  \
+       } else                                                          \
+               *(type *)dest = 0;                                      \
+}                                                                      \
+NOKPROBE_SYMBOL(FETCH_FUNC_NAME(deref, type));
+DEFINE_BASIC_FETCH_FUNCS(deref)
+DEFINE_FETCH_deref(string)
+
+void FETCH_FUNC_NAME(deref, string_size)(struct pt_regs *regs,
+                                        void *data, void *dest)
+{
+       struct deref_fetch_param *dprm = data;
+       unsigned long addr;
+
+       call_fetch(&dprm->orig, regs, &addr);
+       if (addr && dprm->fetch_size) {
+               addr += dprm->offset;
+               dprm->fetch_size(regs, (void *)addr, dest);
+       } else
+               *(string_size *)dest = 0;
+}
+NOKPROBE_SYMBOL(FETCH_FUNC_NAME(deref, string_size));
+
+static void update_deref_fetch_param(struct deref_fetch_param *data)
+{
+       if (CHECK_FETCH_FUNCS(deref, data->orig.fn))
+               update_deref_fetch_param(data->orig.data);
+       else if (CHECK_FETCH_FUNCS(symbol, data->orig.fn))
+               update_symbol_cache(data->orig.data);
+}
+NOKPROBE_SYMBOL(update_deref_fetch_param);
+
+static void free_deref_fetch_param(struct deref_fetch_param *data)
+{
+       if (CHECK_FETCH_FUNCS(deref, data->orig.fn))
+               free_deref_fetch_param(data->orig.data);
+       else if (CHECK_FETCH_FUNCS(symbol, data->orig.fn))
+               free_symbol_cache(data->orig.data);
+       kfree(data);
+}
+NOKPROBE_SYMBOL(free_deref_fetch_param);
+
+/* Bitfield fetch function */
+struct bitfield_fetch_param {
+       struct fetch_param      orig;
+       unsigned char           hi_shift;
+       unsigned char           low_shift;
+};
+
+#define DEFINE_FETCH_bitfield(type)                                    \
+void FETCH_FUNC_NAME(bitfield, type)(struct pt_regs *regs,             \
+                                    void *data, void *dest)            \
+{                                                                      \
+       struct bitfield_fetch_param *bprm = data;                       \
+       type buf = 0;                                                   \
+       call_fetch(&bprm->orig, regs, &buf);                            \
+       if (buf) {                                                      \
+               buf <<= bprm->hi_shift;                                 \
+               buf >>= bprm->low_shift;                                \
+       }                                                               \
+       *(type *)dest = buf;                                            \
+}                                                                      \
+NOKPROBE_SYMBOL(FETCH_FUNC_NAME(bitfield, type));
+DEFINE_BASIC_FETCH_FUNCS(bitfield)
+#define fetch_bitfield_string          NULL
+#define fetch_bitfield_string_size     NULL
+
+static void
+update_bitfield_fetch_param(struct bitfield_fetch_param *data)
+{
+       /*
+        * Don't check the bitfield itself, because this must be the
+        * last fetch function.
+        */
+       if (CHECK_FETCH_FUNCS(deref, data->orig.fn))
+               update_deref_fetch_param(data->orig.data);
+       else if (CHECK_FETCH_FUNCS(symbol, data->orig.fn))
+               update_symbol_cache(data->orig.data);
+}
+
+static void
+free_bitfield_fetch_param(struct bitfield_fetch_param *data)
+{
+       /*
+        * Don't check the bitfield itself, because this must be the
+        * last fetch function.
+        */
+       if (CHECK_FETCH_FUNCS(deref, data->orig.fn))
+               free_deref_fetch_param(data->orig.data);
+       else if (CHECK_FETCH_FUNCS(symbol, data->orig.fn))
+               free_symbol_cache(data->orig.data);
+
+       kfree(data);
+}
+
+static const struct fetch_type *find_fetch_type(const char *type,
+                                               const struct fetch_type *ftbl)
+{
+       int i;
+
+       if (!type)
+               type = DEFAULT_FETCH_TYPE_STR;
+
+       /* Special case: bitfield */
+       if (*type == 'b') {
+               unsigned long bs;
+
+               type = strchr(type, '/');
+               if (!type)
+                       goto fail;
+
+               type++;
+               if (kstrtoul(type, 0, &bs))
+                       goto fail;
+
+               switch (bs) {
+               case 8:
+                       return find_fetch_type("u8", ftbl);
+               case 16:
+                       return find_fetch_type("u16", ftbl);
+               case 32:
+                       return find_fetch_type("u32", ftbl);
+               case 64:
+                       return find_fetch_type("u64", ftbl);
+               default:
+                       goto fail;
+               }
+       }
+
+       for (i = 0; ftbl[i].name; i++) {
+               if (strcmp(type, ftbl[i].name) == 0)
+                       return &ftbl[i];
+       }
+
+fail:
+       return NULL;
+}
+
+/* Special function : only accept unsigned long */
+static void fetch_kernel_stack_address(struct pt_regs *regs, void *dummy, void *dest)
+{
+       *(unsigned long *)dest = kernel_stack_pointer(regs);
+}
+NOKPROBE_SYMBOL(fetch_kernel_stack_address);
+
+static void fetch_user_stack_address(struct pt_regs *regs, void *dummy, void *dest)
+{
+       *(unsigned long *)dest = user_stack_pointer(regs);
+}
+NOKPROBE_SYMBOL(fetch_user_stack_address);
+
+static fetch_func_t get_fetch_size_function(const struct fetch_type *type,
+                                           fetch_func_t orig_fn,
+                                           const struct fetch_type *ftbl)
+{
+       int i;
+
+       if (type != &ftbl[FETCH_TYPE_STRING])
+               return NULL;    /* Only string type needs size function */
+
+       for (i = 0; i < FETCH_MTD_END; i++)
+               if (type->fetch[i] == orig_fn)
+                       return ftbl[FETCH_TYPE_STRSIZE].fetch[i];
+
+       WARN_ON(1);     /* This should not happen */
+
+       return NULL;
+}
+
+/* Split symbol and offset. */
+int traceprobe_split_symbol_offset(char *symbol, unsigned long *offset)
+{
+       char *tmp;
+       int ret;
+
+       if (!offset)
+               return -EINVAL;
+
+       tmp = strchr(symbol, '+');
+       if (tmp) {
+               /* skip sign because kstrtoul doesn't accept '+' */
+               ret = kstrtoul(tmp + 1, 0, offset);
+               if (ret)
+                       return ret;
+
+               *tmp = '\0';
+       } else
+               *offset = 0;
+
+       return 0;
+}
+
+#define PARAM_MAX_STACK (THREAD_SIZE / sizeof(unsigned long))
+
+static int parse_probe_vars(char *arg, const struct fetch_type *t,
+                           struct fetch_param *f, bool is_return,
+                           bool is_kprobe)
+{
+       int ret = 0;
+       unsigned long param;
+
+       if (strcmp(arg, "retval") == 0) {
+               if (is_return)
+                       f->fn = t->fetch[FETCH_MTD_retval];
+               else
+                       ret = -EINVAL;
+       } else if (strncmp(arg, "stack", 5) == 0) {
+               if (arg[5] == '\0') {
+                       if (strcmp(t->name, DEFAULT_FETCH_TYPE_STR))
+                               return -EINVAL;
+
+                       if (is_kprobe)
+                               f->fn = fetch_kernel_stack_address;
+                       else
+                               f->fn = fetch_user_stack_address;
+               } else if (isdigit(arg[5])) {
+                       ret = kstrtoul(arg + 5, 10, &param);
+                       if (ret || (is_kprobe && param > PARAM_MAX_STACK))
+                               ret = -EINVAL;
+                       else {
+                               f->fn = t->fetch[FETCH_MTD_stack];
+                               f->data = (void *)param;
+                       }
+               } else
+                       ret = -EINVAL;
+       } else
+               ret = -EINVAL;
+
+       return ret;
+}
+
+/* Recursive argument parser */
+static int parse_probe_arg(char *arg, const struct fetch_type *t,
+                    struct fetch_param *f, bool is_return, bool is_kprobe,
+                    const struct fetch_type *ftbl)
+{
+       unsigned long param;
+       long offset;
+       char *tmp;
+       int ret = 0;
+
+       switch (arg[0]) {
+       case '$':
+               ret = parse_probe_vars(arg + 1, t, f, is_return, is_kprobe);
+               break;
+
+       case '%':       /* named register */
+               ret = regs_query_register_offset(arg + 1);
+               if (ret >= 0) {
+                       f->fn = t->fetch[FETCH_MTD_reg];
+                       f->data = (void *)(unsigned long)ret;
+                       ret = 0;
+               }
+               break;
+
+       case '@':       /* memory, file-offset or symbol */
+               if (isdigit(arg[1])) {
+                       ret = kstrtoul(arg + 1, 0, &param);
+                       if (ret)
+                               break;
+
+                       f->fn = t->fetch[FETCH_MTD_memory];
+                       f->data = (void *)param;
+               } else if (arg[1] == '+') {
+                       /* kprobes don't support file offsets */
+                       if (is_kprobe)
+                               return -EINVAL;
+
+                       ret = kstrtol(arg + 2, 0, &offset);
+                       if (ret)
+                               break;
+
+                       f->fn = t->fetch[FETCH_MTD_file_offset];
+                       f->data = (void *)offset;
+               } else {
+                       /* uprobes don't support symbols */
+                       if (!is_kprobe)
+                               return -EINVAL;
+
+                       ret = traceprobe_split_symbol_offset(arg + 1, &offset);
+                       if (ret)
+                               break;
+
+                       f->data = alloc_symbol_cache(arg + 1, offset);
+                       if (f->data)
+                               f->fn = t->fetch[FETCH_MTD_symbol];
+               }
+               break;
+
+       case '+':       /* deref memory */
+               arg++;  /* Skip '+', because kstrtol() rejects it. */
+       case '-':
+               tmp = strchr(arg, '(');
+               if (!tmp)
+                       break;
+
+               *tmp = '\0';
+               ret = kstrtol(arg, 0, &offset);
+
+               if (ret)
+                       break;
+
+               arg = tmp + 1;
+               tmp = strrchr(arg, ')');
+
+               if (tmp) {
+                       struct deref_fetch_param        *dprm;
+                       const struct fetch_type         *t2;
+
+                       t2 = find_fetch_type(NULL, ftbl);
+                       *tmp = '\0';
+                       dprm = kzalloc(sizeof(struct deref_fetch_param), GFP_KERNEL);
+
+                       if (!dprm)
+                               return -ENOMEM;
+
+                       dprm->offset = offset;
+                       dprm->fetch = t->fetch[FETCH_MTD_memory];
+                       dprm->fetch_size = get_fetch_size_function(t,
+                                                       dprm->fetch, ftbl);
+                       ret = parse_probe_arg(arg, t2, &dprm->orig, is_return,
+                                                       is_kprobe, ftbl);
+                       if (ret)
+                               kfree(dprm);
+                       else {
+                               f->fn = t->fetch[FETCH_MTD_deref];
+                               f->data = (void *)dprm;
+                       }
+               }
+               break;
+       }
+       if (!ret && !f->fn) {   /* Parsed, but do not find fetch method */
+               pr_info("%s type has no corresponding fetch method.\n", t->name);
+               ret = -EINVAL;
+       }
+
+       return ret;
+}
+
+#define BYTES_TO_BITS(nb)      ((BITS_PER_LONG * (nb)) / sizeof(long))
+
+/* Bitfield type needs to be parsed into a fetch function */
+static int __parse_bitfield_probe_arg(const char *bf,
+                                     const struct fetch_type *t,
+                                     struct fetch_param *f)
+{
+       struct bitfield_fetch_param *bprm;
+       unsigned long bw, bo;
+       char *tail;
+
+       if (*bf != 'b')
+               return 0;
+
+       bprm = kzalloc(sizeof(*bprm), GFP_KERNEL);
+       if (!bprm)
+               return -ENOMEM;
+
+       bprm->orig = *f;
+       f->fn = t->fetch[FETCH_MTD_bitfield];
+       f->data = (void *)bprm;
+       bw = simple_strtoul(bf + 1, &tail, 0);  /* Use simple one */
+
+       if (bw == 0 || *tail != '@')
+               return -EINVAL;
+
+       bf = tail + 1;
+       bo = simple_strtoul(bf, &tail, 0);
+
+       if (tail == bf || *tail != '/')
+               return -EINVAL;
+
+       bprm->hi_shift = BYTES_TO_BITS(t->size) - (bw + bo);
+       bprm->low_shift = bprm->hi_shift + bo;
+
+       return (BYTES_TO_BITS(t->size) < (bw + bo)) ? -EINVAL : 0;
+}
+
+/* String length checking wrapper */
+int traceprobe_parse_probe_arg(char *arg, ssize_t *size,
+               struct probe_arg *parg, bool is_return, bool is_kprobe,
+               const struct fetch_type *ftbl)
+{
+       const char *t;
+       int ret;
+
+       if (strlen(arg) > MAX_ARGSTR_LEN) {
+               pr_info("Argument is too long.: %s\n",  arg);
+               return -ENOSPC;
+       }
+       parg->comm = kstrdup(arg, GFP_KERNEL);
+       if (!parg->comm) {
+               pr_info("Failed to allocate memory for command '%s'.\n", arg);
+               return -ENOMEM;
+       }
+       t = strchr(parg->comm, ':');
+       if (t) {
+               arg[t - parg->comm] = '\0';
+               t++;
+       }
+       parg->type = find_fetch_type(t, ftbl);
+       if (!parg->type) {
+               pr_info("Unsupported type: %s\n", t);
+               return -EINVAL;
+       }
+       parg->offset = *size;
+       *size += parg->type->size;
+       ret = parse_probe_arg(arg, parg->type, &parg->fetch, is_return,
+                             is_kprobe, ftbl);
+
+       if (ret >= 0 && t != NULL)
+               ret = __parse_bitfield_probe_arg(t, parg->type, &parg->fetch);
+
+       if (ret >= 0) {
+               parg->fetch_size.fn = get_fetch_size_function(parg->type,
+                                                             parg->fetch.fn,
+                                                             ftbl);
+               parg->fetch_size.data = parg->fetch.data;
+       }
+
+       return ret;
+}
+
+/* Return 1 if name is reserved or already used by another argument */
+int traceprobe_conflict_field_name(const char *name,
+                              struct probe_arg *args, int narg)
+{
+       int i;
+
+       for (i = 0; i < ARRAY_SIZE(reserved_field_names); i++)
+               if (strcmp(reserved_field_names[i], name) == 0)
+                       return 1;
+
+       for (i = 0; i < narg; i++)
+               if (strcmp(args[i].name, name) == 0)
+                       return 1;
+
+       return 0;
+}
+
+void traceprobe_update_arg(struct probe_arg *arg)
+{
+       if (CHECK_FETCH_FUNCS(bitfield, arg->fetch.fn))
+               update_bitfield_fetch_param(arg->fetch.data);
+       else if (CHECK_FETCH_FUNCS(deref, arg->fetch.fn))
+               update_deref_fetch_param(arg->fetch.data);
+       else if (CHECK_FETCH_FUNCS(symbol, arg->fetch.fn))
+               update_symbol_cache(arg->fetch.data);
+}
+
+void traceprobe_free_probe_arg(struct probe_arg *arg)
+{
+       if (CHECK_FETCH_FUNCS(bitfield, arg->fetch.fn))
+               free_bitfield_fetch_param(arg->fetch.data);
+       else if (CHECK_FETCH_FUNCS(deref, arg->fetch.fn))
+               free_deref_fetch_param(arg->fetch.data);
+       else if (CHECK_FETCH_FUNCS(symbol, arg->fetch.fn))
+               free_symbol_cache(arg->fetch.data);
+
+       kfree(arg->name);
+       kfree(arg->comm);
+}
+
+int traceprobe_command(const char *buf, int (*createfn)(int, char **))
+{
+       char **argv;
+       int argc, ret;
+
+       argc = 0;
+       ret = 0;
+       argv = argv_split(GFP_KERNEL, buf, &argc);
+       if (!argv)
+               return -ENOMEM;
+
+       if (argc)
+               ret = createfn(argc, argv);
+
+       argv_free(argv);
+
+       return ret;
+}
+
+#define WRITE_BUFSIZE  4096
+
+ssize_t traceprobe_probes_write(struct file *file, const char __user *buffer,
+                               size_t count, loff_t *ppos,
+                               int (*createfn)(int, char **))
+{
+       char *kbuf, *tmp;
+       int ret = 0;
+       size_t done = 0;
+       size_t size;
+
+       kbuf = kmalloc(WRITE_BUFSIZE, GFP_KERNEL);
+       if (!kbuf)
+               return -ENOMEM;
+
+       while (done < count) {
+               size = count - done;
+
+               if (size >= WRITE_BUFSIZE)
+                       size = WRITE_BUFSIZE - 1;
+
+               if (copy_from_user(kbuf, buffer + done, size)) {
+                       ret = -EFAULT;
+                       goto out;
+               }
+               kbuf[size] = '\0';
+               tmp = strchr(kbuf, '\n');
+
+               if (tmp) {
+                       *tmp = '\0';
+                       size = tmp - kbuf + 1;
+               } else if (done + size < count) {
+                       pr_warning("Line length is too long: "
+                                  "Should be less than %d.", WRITE_BUFSIZE);
+                       ret = -EINVAL;
+                       goto out;
+               }
+               done += size;
+               /* Remove comments */
+               tmp = strchr(kbuf, '#');
+
+               if (tmp)
+                       *tmp = '\0';
+
+               ret = traceprobe_command(kbuf, createfn);
+               if (ret)
+                       goto out;
+       }
+       ret = done;
+
+out:
+       kfree(kbuf);
+
+       return ret;
+}
+
+static int __set_print_fmt(struct trace_probe *tp, char *buf, int len,
+                          bool is_return)
+{
+       int i;
+       int pos = 0;
+
+       const char *fmt, *arg;
+
+       if (!is_return) {
+               fmt = "(%lx)";
+               arg = "REC->" FIELD_STRING_IP;
+       } else {
+               fmt = "(%lx <- %lx)";
+               arg = "REC->" FIELD_STRING_FUNC ", REC->" FIELD_STRING_RETIP;
+       }
+
+       /* When len=0, we just calculate the needed length */
+#define LEN_OR_ZERO (len ? len - pos : 0)
+
+       pos += snprintf(buf + pos, LEN_OR_ZERO, "\"%s", fmt);
+
+       for (i = 0; i < tp->nr_args; i++) {
+               pos += snprintf(buf + pos, LEN_OR_ZERO, " %s=%s",
+                               tp->args[i].name, tp->args[i].type->fmt);
+       }
+
+       pos += snprintf(buf + pos, LEN_OR_ZERO, "\", %s", arg);
+
+       for (i = 0; i < tp->nr_args; i++) {
+               if (strcmp(tp->args[i].type->name, "string") == 0)
+                       pos += snprintf(buf + pos, LEN_OR_ZERO,
+                                       ", __get_str(%s)",
+                                       tp->args[i].name);
+               else
+                       pos += snprintf(buf + pos, LEN_OR_ZERO, ", REC->%s",
+                                       tp->args[i].name);
+       }
+
+#undef LEN_OR_ZERO
+
+       /* return the length of print_fmt */
+       return pos;
+}
+
+int set_print_fmt(struct trace_probe *tp, bool is_return)
+{
+       int len;
+       char *print_fmt;
+
+       /* First: called with 0 length to calculate the needed length */
+       len = __set_print_fmt(tp, NULL, 0, is_return);
+       print_fmt = kmalloc(len + 1, GFP_KERNEL);
+       if (!print_fmt)
+               return -ENOMEM;
+
+       /* Second: actually write the @print_fmt */
+       __set_print_fmt(tp, print_fmt, len + 1, is_return);
+       tp->call.print_fmt = print_fmt;
+
+       return 0;
+}