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Diffstat (limited to 'kernel/trace/trace_probe.c')
-rw-r--r--kernel/trace/trace_probe.c440
1 files changed, 161 insertions, 279 deletions
diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 412e959709b4..8364a421b4df 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -35,46 +35,27 @@ const char *reserved_field_names[] = {
FIELD_STRING_FUNC,
};
-/* Printing function type */
-#define PRINT_TYPE_FUNC_NAME(type) print_type_##type
-#define PRINT_TYPE_FMT_NAME(type) print_type_format_##type
-
/* Printing in basic type function template */
-#define DEFINE_BASIC_PRINT_TYPE_FUNC(type, fmt, cast) \
-static __kprobes int PRINT_TYPE_FUNC_NAME(type)(struct trace_seq *s, \
+#define DEFINE_BASIC_PRINT_TYPE_FUNC(type, fmt) \
+__kprobes int PRINT_TYPE_FUNC_NAME(type)(struct trace_seq *s, \
const char *name, \
- void *data, void *ent)\
+ void *data, void *ent) \
{ \
- return trace_seq_printf(s, " %s=" fmt, name, (cast)*(type *)data);\
+ return trace_seq_printf(s, " %s=" fmt, name, *(type *)data); \
} \
-static const char PRINT_TYPE_FMT_NAME(type)[] = fmt;
-
-DEFINE_BASIC_PRINT_TYPE_FUNC(u8, "%x", unsigned int)
-DEFINE_BASIC_PRINT_TYPE_FUNC(u16, "%x", unsigned int)
-DEFINE_BASIC_PRINT_TYPE_FUNC(u32, "%lx", unsigned long)
-DEFINE_BASIC_PRINT_TYPE_FUNC(u64, "%llx", unsigned long long)
-DEFINE_BASIC_PRINT_TYPE_FUNC(s8, "%d", int)
-DEFINE_BASIC_PRINT_TYPE_FUNC(s16, "%d", int)
-DEFINE_BASIC_PRINT_TYPE_FUNC(s32, "%ld", long)
-DEFINE_BASIC_PRINT_TYPE_FUNC(s64, "%lld", long long)
-
-static inline void *get_rloc_data(u32 *dl)
-{
- return (u8 *)dl + get_rloc_offs(*dl);
-}
+const char PRINT_TYPE_FMT_NAME(type)[] = fmt;
-/* For data_loc conversion */
-static inline void *get_loc_data(u32 *dl, void *ent)
-{
- return (u8 *)ent + get_rloc_offs(*dl);
-}
-
-/* For defining macros, define string/string_size types */
-typedef u32 string;
-typedef u32 string_size;
+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 */
-static __kprobes int PRINT_TYPE_FUNC_NAME(string)(struct trace_seq *s,
+__kprobes int PRINT_TYPE_FUNC_NAME(string)(struct trace_seq *s,
const char *name,
void *data, void *ent)
{
@@ -87,18 +68,7 @@ static __kprobes int PRINT_TYPE_FUNC_NAME(string)(struct trace_seq *s,
(const char *)get_loc_data(data, ent));
}
-static const char PRINT_TYPE_FMT_NAME(string)[] = "\\\"%s\\\"";
-
-#define FETCH_FUNC_NAME(method, type) fetch_##method##_##type
-/*
- * Define macro for basic types - we don't need to define s* types, because
- * we have to care only about bitwidth at recording time.
- */
-#define DEFINE_BASIC_FETCH_FUNCS(method) \
-DEFINE_FETCH_##method(u8) \
-DEFINE_FETCH_##method(u16) \
-DEFINE_FETCH_##method(u32) \
-DEFINE_FETCH_##method(u64)
+const char PRINT_TYPE_FMT_NAME(string)[] = "\\\"%s\\\"";
#define CHECK_FETCH_FUNCS(method, fn) \
(((FETCH_FUNC_NAME(method, u8) == fn) || \
@@ -111,7 +81,7 @@ DEFINE_FETCH_##method(u64)
/* Data fetch function templates */
#define DEFINE_FETCH_reg(type) \
-static __kprobes void FETCH_FUNC_NAME(reg, type)(struct pt_regs *regs, \
+__kprobes void FETCH_FUNC_NAME(reg, type)(struct pt_regs *regs, \
void *offset, void *dest) \
{ \
*(type *)dest = (type)regs_get_register(regs, \
@@ -122,20 +92,8 @@ DEFINE_BASIC_FETCH_FUNCS(reg)
#define fetch_reg_string NULL
#define fetch_reg_string_size NULL
-#define DEFINE_FETCH_stack(type) \
-static __kprobes void FETCH_FUNC_NAME(stack, type)(struct pt_regs *regs,\
- void *offset, void *dest) \
-{ \
- *(type *)dest = (type)regs_get_kernel_stack_nth(regs, \
- (unsigned int)((unsigned long)offset)); \
-}
-DEFINE_BASIC_FETCH_FUNCS(stack)
-/* No string on the stack entry */
-#define fetch_stack_string NULL
-#define fetch_stack_string_size NULL
-
#define DEFINE_FETCH_retval(type) \
-static __kprobes void FETCH_FUNC_NAME(retval, type)(struct pt_regs *regs,\
+__kprobes void FETCH_FUNC_NAME(retval, type)(struct pt_regs *regs, \
void *dummy, void *dest) \
{ \
*(type *)dest = (type)regs_return_value(regs); \
@@ -145,150 +103,16 @@ DEFINE_BASIC_FETCH_FUNCS(retval)
#define fetch_retval_string NULL
#define fetch_retval_string_size NULL
-#define DEFINE_FETCH_memory(type) \
-static __kprobes void FETCH_FUNC_NAME(memory, type)(struct pt_regs *regs,\
- void *addr, void *dest) \
-{ \
- type retval; \
- if (probe_kernel_address(addr, retval)) \
- *(type *)dest = 0; \
- else \
- *(type *)dest = retval; \
-}
-DEFINE_BASIC_FETCH_FUNCS(memory)
-/*
- * Fetch a null-terminated string. Caller MUST set *(u32 *)dest with max
- * length and relative data location.
- */
-static __kprobes void FETCH_FUNC_NAME(memory, string)(struct pt_regs *regs,
- void *addr, void *dest)
-{
- long ret;
- int maxlen = get_rloc_len(*(u32 *)dest);
- u8 *dst = get_rloc_data(dest);
- u8 *src = addr;
- mm_segment_t old_fs = get_fs();
-
- if (!maxlen)
- return;
-
- /*
- * Try to get string again, since the string can be changed while
- * probing.
- */
- set_fs(KERNEL_DS);
- pagefault_disable();
-
- do
- ret = __copy_from_user_inatomic(dst++, src++, 1);
- while (dst[-1] && ret == 0 && src - (u8 *)addr < maxlen);
-
- dst[-1] = '\0';
- pagefault_enable();
- set_fs(old_fs);
-
- if (ret < 0) { /* Failed to fetch string */
- ((u8 *)get_rloc_data(dest))[0] = '\0';
- *(u32 *)dest = make_data_rloc(0, get_rloc_offs(*(u32 *)dest));
- } else {
- *(u32 *)dest = make_data_rloc(src - (u8 *)addr,
- get_rloc_offs(*(u32 *)dest));
- }
-}
-
-/* Return the length of string -- including null terminal byte */
-static __kprobes void FETCH_FUNC_NAME(memory, string_size)(struct pt_regs *regs,
- void *addr, void *dest)
-{
- mm_segment_t old_fs;
- int ret, len = 0;
- u8 c;
-
- old_fs = get_fs();
- set_fs(KERNEL_DS);
- pagefault_disable();
-
- do {
- ret = __copy_from_user_inatomic(&c, (u8 *)addr + len, 1);
- len++;
- } while (c && ret == 0 && len < MAX_STRING_SIZE);
-
- pagefault_enable();
- set_fs(old_fs);
-
- if (ret < 0) /* Failed to check the length */
- *(u32 *)dest = 0;
- else
- *(u32 *)dest = len;
-}
-
-/* Memory fetching by symbol */
-struct symbol_cache {
- char *symbol;
- long offset;
- unsigned long addr;
-};
-
-static unsigned long update_symbol_cache(struct symbol_cache *sc)
-{
- sc->addr = (unsigned long)kallsyms_lookup_name(sc->symbol);
-
- if (sc->addr)
- sc->addr += sc->offset;
-
- return sc->addr;
-}
-
-static void free_symbol_cache(struct symbol_cache *sc)
-{
- kfree(sc->symbol);
- kfree(sc);
-}
-
-static struct symbol_cache *alloc_symbol_cache(const char *sym, long offset)
-{
- struct symbol_cache *sc;
-
- if (!sym || strlen(sym) == 0)
- return NULL;
-
- sc = kzalloc(sizeof(struct symbol_cache), GFP_KERNEL);
- if (!sc)
- return NULL;
-
- sc->symbol = kstrdup(sym, GFP_KERNEL);
- if (!sc->symbol) {
- kfree(sc);
- return NULL;
- }
- sc->offset = offset;
- update_symbol_cache(sc);
-
- return sc;
-}
-
-#define DEFINE_FETCH_symbol(type) \
-static __kprobes void FETCH_FUNC_NAME(symbol, type)(struct pt_regs *regs,\
- void *data, void *dest) \
-{ \
- struct symbol_cache *sc = data; \
- if (sc->addr) \
- fetch_memory_##type(regs, (void *)sc->addr, dest); \
- else \
- *(type *)dest = 0; \
-}
-DEFINE_BASIC_FETCH_FUNCS(symbol)
-DEFINE_FETCH_symbol(string)
-DEFINE_FETCH_symbol(string_size)
-
/* 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) \
-static __kprobes void FETCH_FUNC_NAME(deref, type)(struct pt_regs *regs,\
+__kprobes void FETCH_FUNC_NAME(deref, type)(struct pt_regs *regs, \
void *data, void *dest) \
{ \
struct deref_fetch_param *dprm = data; \
@@ -296,13 +120,26 @@ static __kprobes void FETCH_FUNC_NAME(deref, type)(struct pt_regs *regs,\
call_fetch(&dprm->orig, regs, &addr); \
if (addr) { \
addr += dprm->offset; \
- fetch_memory_##type(regs, (void *)addr, dest); \
+ dprm->fetch(regs, (void *)addr, dest); \
} else \
*(type *)dest = 0; \
}
DEFINE_BASIC_FETCH_FUNCS(deref)
DEFINE_FETCH_deref(string)
-DEFINE_FETCH_deref(string_size)
+
+__kprobes 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;
+}
static __kprobes void update_deref_fetch_param(struct deref_fetch_param *data)
{
@@ -329,7 +166,7 @@ struct bitfield_fetch_param {
};
#define DEFINE_FETCH_bitfield(type) \
-static __kprobes void FETCH_FUNC_NAME(bitfield, type)(struct pt_regs *regs,\
+__kprobes void FETCH_FUNC_NAME(bitfield, type)(struct pt_regs *regs, \
void *data, void *dest) \
{ \
struct bitfield_fetch_param *bprm = data; \
@@ -374,58 +211,8 @@ free_bitfield_fetch_param(struct bitfield_fetch_param *data)
kfree(data);
}
-/* Default (unsigned long) fetch type */
-#define __DEFAULT_FETCH_TYPE(t) u##t
-#define _DEFAULT_FETCH_TYPE(t) __DEFAULT_FETCH_TYPE(t)
-#define DEFAULT_FETCH_TYPE _DEFAULT_FETCH_TYPE(BITS_PER_LONG)
-#define DEFAULT_FETCH_TYPE_STR __stringify(DEFAULT_FETCH_TYPE)
-
-#define ASSIGN_FETCH_FUNC(method, type) \
- [FETCH_MTD_##method] = FETCH_FUNC_NAME(method, type)
-
-#define __ASSIGN_FETCH_TYPE(_name, ptype, ftype, _size, sign, _fmttype) \
- {.name = _name, \
- .size = _size, \
- .is_signed = sign, \
- .print = PRINT_TYPE_FUNC_NAME(ptype), \
- .fmt = PRINT_TYPE_FMT_NAME(ptype), \
- .fmttype = _fmttype, \
- .fetch = { \
-ASSIGN_FETCH_FUNC(reg, ftype), \
-ASSIGN_FETCH_FUNC(stack, ftype), \
-ASSIGN_FETCH_FUNC(retval, ftype), \
-ASSIGN_FETCH_FUNC(memory, ftype), \
-ASSIGN_FETCH_FUNC(symbol, ftype), \
-ASSIGN_FETCH_FUNC(deref, ftype), \
-ASSIGN_FETCH_FUNC(bitfield, ftype), \
- } \
- }
-
-#define ASSIGN_FETCH_TYPE(ptype, ftype, sign) \
- __ASSIGN_FETCH_TYPE(#ptype, ptype, ftype, sizeof(ftype), sign, #ptype)
-
-#define FETCH_TYPE_STRING 0
-#define FETCH_TYPE_STRSIZE 1
-
-/* Fetch type information table */
-static const struct fetch_type fetch_type_table[] = {
- /* Special types */
- [FETCH_TYPE_STRING] = __ASSIGN_FETCH_TYPE("string", string, string,
- sizeof(u32), 1, "__data_loc char[]"),
- [FETCH_TYPE_STRSIZE] = __ASSIGN_FETCH_TYPE("string_size", u32,
- string_size, sizeof(u32), 0, "u32"),
- /* Basic types */
- ASSIGN_FETCH_TYPE(u8, u8, 0),
- ASSIGN_FETCH_TYPE(u16, u16, 0),
- ASSIGN_FETCH_TYPE(u32, u32, 0),
- ASSIGN_FETCH_TYPE(u64, u64, 0),
- ASSIGN_FETCH_TYPE(s8, u8, 1),
- ASSIGN_FETCH_TYPE(s16, u16, 1),
- ASSIGN_FETCH_TYPE(s32, u32, 1),
- ASSIGN_FETCH_TYPE(s64, u64, 1),
-};
-
-static const struct fetch_type *find_fetch_type(const char *type)
+static const struct fetch_type *find_fetch_type(const char *type,
+ const struct fetch_type *ftbl)
{
int i;
@@ -446,44 +233,52 @@ static const struct fetch_type *find_fetch_type(const char *type)
switch (bs) {
case 8:
- return find_fetch_type("u8");
+ return find_fetch_type("u8", ftbl);
case 16:
- return find_fetch_type("u16");
+ return find_fetch_type("u16", ftbl);
case 32:
- return find_fetch_type("u32");
+ return find_fetch_type("u32", ftbl);
case 64:
- return find_fetch_type("u64");
+ return find_fetch_type("u64", ftbl);
default:
goto fail;
}
}
- for (i = 0; i < ARRAY_SIZE(fetch_type_table); i++)
- if (strcmp(type, fetch_type_table[i].name) == 0)
- return &fetch_type_table[i];
+ 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 __kprobes void fetch_stack_address(struct pt_regs *regs,
- void *dummy, void *dest)
+static __kprobes void fetch_kernel_stack_address(struct pt_regs *regs,
+ void *dummy, void *dest)
{
*(unsigned long *)dest = kernel_stack_pointer(regs);
}
+static __kprobes void fetch_user_stack_address(struct pt_regs *regs,
+ void *dummy, void *dest)
+{
+ *(unsigned long *)dest = user_stack_pointer(regs);
+}
+
static fetch_func_t get_fetch_size_function(const struct fetch_type *type,
- fetch_func_t orig_fn)
+ fetch_func_t orig_fn,
+ const struct fetch_type *ftbl)
{
int i;
- if (type != &fetch_type_table[FETCH_TYPE_STRING])
+ 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 fetch_type_table[FETCH_TYPE_STRSIZE].fetch[i];
+ return ftbl[FETCH_TYPE_STRSIZE].fetch[i];
WARN_ON(1); /* This should not happen */
@@ -516,7 +311,8 @@ int traceprobe_split_symbol_offset(char *symbol, unsigned long *offset)
#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)
+ struct fetch_param *f, bool is_return,
+ bool is_kprobe)
{
int ret = 0;
unsigned long param;
@@ -528,13 +324,16 @@ static int parse_probe_vars(char *arg, const struct fetch_type *t,
ret = -EINVAL;
} else if (strncmp(arg, "stack", 5) == 0) {
if (arg[5] == '\0') {
- if (strcmp(t->name, DEFAULT_FETCH_TYPE_STR) == 0)
- f->fn = fetch_stack_address;
+ if (strcmp(t->name, DEFAULT_FETCH_TYPE_STR))
+ return -EINVAL;
+
+ if (is_kprobe)
+ f->fn = fetch_kernel_stack_address;
else
- ret = -EINVAL;
+ f->fn = fetch_user_stack_address;
} else if (isdigit(arg[5])) {
ret = kstrtoul(arg + 5, 10, &param);
- if (ret || param > PARAM_MAX_STACK)
+ if (ret || (is_kprobe && param > PARAM_MAX_STACK))
ret = -EINVAL;
else {
f->fn = t->fetch[FETCH_MTD_stack];
@@ -552,20 +351,18 @@ static int parse_probe_vars(char *arg, const struct fetch_type *t,
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;
-
- ret = 0;
+ int ret = 0;
- /* Until uprobe_events supports only reg arguments */
- if (!is_kprobe && arg[0] != '%')
- return -EINVAL;
+ ftbl = is_kprobe ? kprobes_fetch_type_table : uprobes_fetch_type_table;
+ BUG_ON(ftbl == NULL);
switch (arg[0]) {
case '$':
- ret = parse_probe_vars(arg + 1, t, f, is_return);
+ ret = parse_probe_vars(arg + 1, t, f, is_return, is_kprobe);
break;
case '%': /* named register */
@@ -577,7 +374,7 @@ static int parse_probe_arg(char *arg, const struct fetch_type *t,
}
break;
- case '@': /* memory or symbol */
+ case '@': /* memory, file-offset or symbol */
if (isdigit(arg[1])) {
ret = kstrtoul(arg + 1, 0, &param);
if (ret)
@@ -585,7 +382,22 @@ static int parse_probe_arg(char *arg, const struct fetch_type *t,
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;
@@ -616,7 +428,7 @@ static int parse_probe_arg(char *arg, const struct fetch_type *t,
struct deref_fetch_param *dprm;
const struct fetch_type *t2;
- t2 = find_fetch_type(NULL);
+ t2 = find_fetch_type(NULL, ftbl);
*tmp = '\0';
dprm = kzalloc(sizeof(struct deref_fetch_param), GFP_KERNEL);
@@ -624,6 +436,9 @@ static int parse_probe_arg(char *arg, const struct fetch_type *t,
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);
if (ret)
@@ -685,9 +500,13 @@ static int __parse_bitfield_probe_arg(const char *bf,
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;
+ ftbl = is_kprobe ? kprobes_fetch_type_table : uprobes_fetch_type_table;
+ BUG_ON(ftbl == NULL);
+
if (strlen(arg) > MAX_ARGSTR_LEN) {
pr_info("Argument is too long.: %s\n", arg);
return -ENOSPC;
@@ -702,7 +521,7 @@ int traceprobe_parse_probe_arg(char *arg, ssize_t *size,
arg[t - parg->comm] = '\0';
t++;
}
- parg->type = find_fetch_type(t);
+ parg->type = find_fetch_type(t, ftbl);
if (!parg->type) {
pr_info("Unsupported type: %s\n", t);
return -EINVAL;
@@ -716,7 +535,8 @@ int traceprobe_parse_probe_arg(char *arg, ssize_t *size,
if (ret >= 0) {
parg->fetch_size.fn = get_fetch_size_function(parg->type,
- parg->fetch.fn);
+ parg->fetch.fn,
+ ftbl);
parg->fetch_size.data = parg->fetch.data;
}
@@ -837,3 +657,65 @@ out:
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;
+}