From: Steven Rostedt <[email protected]>
Add syntax to the parsing of eprobes to be able to typecast a trace event
field that is a pointer to a structure.
Currently, a dereference must be a number, where the user has to figure
out manually the offset of a member of a structure that they want to
dereference.
But for event probes that records a field that happens to be a pointer to
a structure, it cannot dereference these values with BTF naming, but
must use numerical offsets.
For example, to find out what device a sk_buff is pointing to in the
net_dev_xmit trace event, one must first use gdb to find the offsets of the
members of the structures:
(gdb) p &((struct sk_buff *)0)->dev
$1 = (struct net_device **) 0x10
(gdb) p &((struct net_device *)0)->name
$2 = (char (*)[16]) 0x118
And then use the raw numbers to dereference:
# echo 'e:xmit net.net_dev_xmit +0x118(+0x10($skbaddr)):string' >>
dynamic_events
If BTF is in the kernel, then instead, the skbaddr can be typecast to
sk_buff and use the normal dereference logic.
# echo 'e:xmit net.net_dev_xmit (sk_buff)skbaddr->dev->name:string' >>
dynamic_events
# echo 1 > events/eprobes/xmit/enable
# cat trace
[..]
sshd-session-1022 [000] b..2. 860.249343: xmit: (net.net_dev_xmit)
arg1="enp7s0"
sshd-session-1022 [000] b..2. 860.250061: xmit: (net.net_dev_xmit)
arg1="enp7s0"
sshd-session-1022 [000] b..2. 860.250142: xmit: (net.net_dev_xmit)
arg1="enp7s0"
sshd-session-1022 [000] b..2. 860.263553: xmit: (net.net_dev_xmit)
arg1="enp7s0"
sshd-session-1022 [000] b..2. 860.283820: xmit: (net.net_dev_xmit)
arg1="enp7s0"
sshd-session-1022 [000] b..2. 860.302716: xmit: (net.net_dev_xmit)
arg1="enp7s0"
sshd-session-1022 [000] b..2. 860.322905: xmit: (net.net_dev_xmit)
arg1="enp7s0"
sshd-session-1022 [000] b..2. 860.342828: xmit: (net.net_dev_xmit)
arg1="enp7s0"
sshd-session-1022 [000] b..2. 860.362268: xmit: (net.net_dev_xmit)
arg1="enp7s0"
sshd-session-1022 [000] b..2. 860.382335: xmit: (net.net_dev_xmit)
arg1="enp7s0"
sshd-session-1022 [000] b..2. 860.400856: xmit: (net.net_dev_xmit)
arg1="enp7s0"
sshd-session-1022 [000] b..2. 860.419893: xmit: (net.net_dev_xmit)
arg1="enp7s0"
The syntax is simply: (STRUCT)(FIELD)->MEMBER[->MEMBER..]
Signed-off-by: Steven Rostedt (Google) <[email protected]>
---
Changes from v4:
https://patch.msgid.link/[email protected]
- Only describe this for eprobes, as that is currently the only user of
this. Kprobes registers can come later. (Sashiko)
- Update the documentation to only be in the eprobetrace.rst.
- Make the btf value separate for structures and functions. As a function
may use a BTF from a module, it can point to a structure that is in
vmlinux. Make them separate and add a ctx_btf() helper function to
figure out which one to use. (Masami Hiramatsu)
- Remove updating query_btf_context() by having it check funcname first.
The above ctx_btf() helper fixes this.
- Rename TPARG_FL_STRUCT to TPARG_FL_TYPECAST (Masami Hiramatsu)
- Have the typecast code call parse_btf_arg() directly, instead of going
through parse_probe_vars(). This fixes issues with updating the pcode
value, and simplifies the formatting and code (Sashiko).
Added a parse_trace_event() helper to duplicate the handling of
TPARG_FL_TEVENT.
- Use "goto found_type;" instead of relying on type being NULL in
parse_btf_arg(). (Masami Hiramatsu)
- Add query_btf_struct() stub function when CONFIG_PROBE_EVENTS_BTF_ARGS
is not defined. (kernel test robot)
- Remove need for '*' in typecast (Masami Hiramatsu)
- Have the event fields not use '$' when the typecast is used.
(Masami Hiramatsu)
Documentation/trace/eprobetrace.rst | 4 +
kernel/trace/trace_probe.c | 158 ++++++++++++++++++++++------
kernel/trace/trace_probe.h | 4 +
3 files changed, 135 insertions(+), 31 deletions(-)
diff --git a/Documentation/trace/eprobetrace.rst
b/Documentation/trace/eprobetrace.rst
index 89b5157cfab8..fe3602540569 100644
--- a/Documentation/trace/eprobetrace.rst
+++ b/Documentation/trace/eprobetrace.rst
@@ -46,6 +46,10 @@ Synopsis of eprobe_events
(x8/x16/x32/x64), VFS layer common type(%pd/%pD), "char",
"string", "ustring", "symbol", "symstr" and "bitfield" are
supported.
+ (STRUCT)FIELD->MEMBER[->MEMBER] : If BTF is supported, typecast FIELD to
+ a pointer to STRUCT and then derference the pointer defined
by
+ ->MEMBER. Note that when this is used, the FIELD name does
not
+ need to be prefixed with a '$'.
Types
-----
diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index e0d3a0da26af..cd54deb985f4 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -376,11 +376,17 @@ static bool btf_type_is_char_array(struct btf *btf, const
struct btf_type *type)
&& BTF_INT_BITS(intdata) == 8;
}
+static struct btf *ctx_btf(struct traceprobe_parse_context *ctx)
+{
+ return ctx->flags & TPARG_FL_TYPECAST ?
+ ctx->struct_btf : ctx->btf;
+}
+
static int check_prepare_btf_string_fetch(char *typename,
struct fetch_insn **pcode,
struct traceprobe_parse_context *ctx)
{
- struct btf *btf = ctx->btf;
+ struct btf *btf = ctx_btf(ctx);
if (!btf || !ctx->last_type)
return 0;
@@ -464,6 +470,27 @@ static const char *fetch_type_from_btf_type(struct btf
*btf,
return NULL;
}
+static int query_btf_struct(const char *sname, struct traceprobe_parse_context
*ctx)
+{
+ int id;
+
+ if (!ctx->struct_btf) {
+ struct btf *btf;
+
+ id = bpf_find_btf_id(sname, BTF_KIND_STRUCT, &btf);
+ if (id < 0)
+ return id;
+ ctx->struct_btf = btf;
+ } else {
+ id = btf_find_by_name_kind(ctx->struct_btf, sname,
BTF_KIND_STRUCT);
+ if (id < 0)
+ return id;
+ }
+
+ ctx->last_struct = btf_type_by_id(ctx->struct_btf, id);
+ return 0;
+}
+
static int query_btf_context(struct traceprobe_parse_context *ctx)
{
const struct btf_param *param;
@@ -515,6 +542,10 @@ static void clear_btf_context(struct
traceprobe_parse_context *ctx)
ctx->params = NULL;
ctx->nr_params = 0;
}
+ if (ctx->struct_btf) {
+ btf_put(ctx->struct_btf);
+ ctx->last_struct = NULL;
+ }
}
/* Return 1 if the field separator is arrow operator ('->') */
@@ -554,22 +585,29 @@ static int parse_btf_field(char *fieldname, const struct
btf_type *type,
struct fetch_insn *code = *pcode;
const struct btf_member *field;
u32 bitoffs, anon_offs;
+ bool is_struct = ctx->flags & TPARG_FL_TYPECAST;
+ struct btf *btf = ctx_btf(ctx);
char *next;
int is_ptr;
s32 tid;
do {
- /* Outer loop for solving arrow operator ('->') */
- if (BTF_INFO_KIND(type->info) != BTF_KIND_PTR) {
- trace_probe_log_err(ctx->offset, NO_PTR_STRCT);
- return -EINVAL;
- }
- /* Convert a struct pointer type to a struct type */
- type = btf_type_skip_modifiers(ctx->btf, type->type, &tid);
- if (!type) {
- trace_probe_log_err(ctx->offset, BAD_BTF_TID);
- return -EINVAL;
+ if (!is_struct) {
+ /* Outer loop for solving arrow operator ('->') */
+ if (BTF_INFO_KIND(type->info) != BTF_KIND_PTR) {
+ trace_probe_log_err(ctx->offset, NO_PTR_STRCT);
+ return -EINVAL;
+ }
+
+ /* Convert a struct pointer type to a struct type */
+ type = btf_type_skip_modifiers(btf, type->type, &tid);
+ if (!type) {
+ trace_probe_log_err(ctx->offset, BAD_BTF_TID);
+ return -EINVAL;
+ }
}
+ /* Only the first type can skip being a pointer */
+ is_struct = false;
bitoffs = 0;
do {
@@ -580,7 +618,7 @@ static int parse_btf_field(char *fieldname, const struct
btf_type *type,
return is_ptr;
anon_offs = 0;
- field = btf_find_struct_member(ctx->btf, type,
fieldname,
+ field = btf_find_struct_member(btf, type, fieldname,
&anon_offs);
if (IS_ERR(field)) {
trace_probe_log_err(ctx->offset, BAD_BTF_TID);
@@ -602,7 +640,7 @@ static int parse_btf_field(char *fieldname, const struct
btf_type *type,
ctx->last_bitsize = 0;
}
- type = btf_type_skip_modifiers(ctx->btf, field->type,
&tid);
+ type = btf_type_skip_modifiers(btf, field->type, &tid);
if (!type) {
trace_probe_log_err(ctx->offset, BAD_BTF_TID);
return -EINVAL;
@@ -627,6 +665,26 @@ static int parse_btf_field(char *fieldname, const struct
btf_type *type,
return 0;
}
+
+static int parse_trace_event(char *arg, struct fetch_insn *code,
+ struct traceprobe_parse_context *ctx)
+{
+ int ret;
+
+ if (code->data)
+ return -EFAULT;
+ ret = parse_trace_event_arg(arg, code, ctx);
+ if (!ret)
+ return 0;
+ if (strcmp(arg, "comm") == 0 || strcmp(arg, "COMM") == 0) {
+ code->op = FETCH_OP_COMM;
+ return 0;
+ }
+ /* backward compatibility */
+ ctx->offset = 0;
+ return -EINVAL;
+}
+
static int __store_entry_arg(struct trace_probe *tp, int argnum);
static int parse_btf_arg(char *varname,
@@ -636,11 +694,12 @@ static int parse_btf_arg(char *varname,
struct fetch_insn *code = *pcode;
const struct btf_param *params;
const struct btf_type *type;
+ struct btf *btf = ctx_btf(ctx);
char *field = NULL;
int i, is_ptr, ret;
u32 tid;
- if (WARN_ON_ONCE(!ctx->funcname))
+ if (WARN_ON_ONCE(!ctx->funcname && !(ctx->flags & TPARG_FL_TYPECAST)))
return -EINVAL;
is_ptr = split_next_field(varname, &field, ctx);
@@ -653,6 +712,14 @@ static int parse_btf_arg(char *varname,
return -EOPNOTSUPP;
}
+ if (ctx->flags & TPARG_FL_TEVENT) {
+ int ret;
+
+ ret = parse_trace_event(varname, code, ctx);
+ if (ret < 0)
+ return ret;
+ }
+
if (ctx->flags & TPARG_FL_RETURN && !strcmp(varname, "$retval")) {
code->op = FETCH_OP_RETVAL;
/* Check whether the function return type is not void */
@@ -672,7 +739,7 @@ static int parse_btf_arg(char *varname,
return 0;
}
- if (!ctx->btf) {
+ if (!btf) {
ret = query_btf_context(ctx);
if (ret < 0 || ctx->nr_params == 0) {
trace_probe_log_err(ctx->offset, NO_BTF_ENTRY);
@@ -682,7 +749,7 @@ static int parse_btf_arg(char *varname,
params = ctx->params;
for (i = 0; i < ctx->nr_params; i++) {
- const char *name = btf_name_by_offset(ctx->btf,
params[i].name_off);
+ const char *name = btf_name_by_offset(btf, params[i].name_off);
if (name && !strcmp(name, varname)) {
if (tparg_is_function_entry(ctx->flags)) {
@@ -704,15 +771,22 @@ static int parse_btf_arg(char *varname,
goto found;
}
}
+
+ if (ctx->flags & TPARG_FL_TYPECAST) {
+ type = ctx->last_struct;
+ goto found_type;
+ }
+
trace_probe_log_err(ctx->offset, NO_BTFARG);
return -ENOENT;
found:
- type = btf_type_skip_modifiers(ctx->btf, tid, &tid);
+ type = btf_type_skip_modifiers(btf, tid, &tid);
if (!type) {
trace_probe_log_err(ctx->offset, BAD_BTF_TID);
return -EINVAL;
}
+found_type:
/* Initialize the last type information */
ctx->last_type = type;
ctx->last_bitoffs = 0;
@@ -727,7 +801,7 @@ static int parse_btf_arg(char *varname,
static const struct fetch_type *find_fetch_type_from_btf_type(
struct traceprobe_parse_context *ctx)
{
- struct btf *btf = ctx->btf;
+ struct btf *btf = ctx_btf(ctx);
const char *typestr = NULL;
if (btf && ctx->last_type)
@@ -764,6 +838,11 @@ static void clear_btf_context(struct
traceprobe_parse_context *ctx)
ctx->btf = NULL;
}
+static int query_btf_struct(const char *sname, struct traceprobe_parse_context
*ctx)
+{
+ return -EOPNOTSUPP;
+}
+
static int query_btf_context(struct traceprobe_parse_context *ctx)
{
return -EOPNOTSUPP;
@@ -953,18 +1032,9 @@ static int parse_probe_vars(char *orig_arg, const struct
fetch_type *t,
int len;
if (ctx->flags & TPARG_FL_TEVENT) {
- if (code->data)
- return -EFAULT;
- ret = parse_trace_event_arg(arg, code, ctx);
- if (!ret)
- return 0;
- if (strcmp(arg, "comm") == 0 || strcmp(arg, "COMM") == 0) {
- code->op = FETCH_OP_COMM;
- return 0;
- }
- /* backward compatibility */
- ctx->offset = 0;
- goto inval;
+ if (parse_trace_event(arg, code, ctx) < 0)
+ goto inval;
+ return 0;
}
if (str_has_prefix(arg, "retval")) {
@@ -1231,6 +1301,30 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
code->op = FETCH_OP_IMM;
}
break;
+ case '(':
+ tmp = strchr(arg, ')');
+ if (!tmp) {
+ trace_probe_log_err(ctx->offset + strlen(arg),
+ DEREF_OPEN_BRACE);
+ return -EINVAL;
+ }
+ *tmp = '\0';
+ ret = query_btf_struct(arg + 1, ctx);
+ *tmp = ')';
+
+ if (ret < 0) {
+ trace_probe_log_err(ctx->offset + 1, NO_PTR_STRCT);
+ return -EINVAL;
+ }
+
+ ctx->flags |= TPARG_FL_TYPECAST;
+ tmp++;
+
+ ctx->offset += tmp - arg;
+ ret = parse_btf_arg(tmp, pcode, end, ctx);
+ ctx->flags &= ~TPARG_FL_TYPECAST;
+ ctx->last_struct = NULL;
+ break;
default:
if (isalpha(arg[0]) || arg[0] == '_') { /* BTF variable */
if (!tparg_is_function_entry(ctx->flags) &&
@@ -1504,6 +1598,7 @@ static int traceprobe_parse_probe_arg_body(const char
*argv, ssize_t *size,
code[FETCH_INSN_MAX - 1].op = FETCH_OP_END;
ctx->last_type = NULL;
+ ctx->last_struct = NULL;
ret = parse_probe_arg(arg, parg->type, &code, &code[FETCH_INSN_MAX - 1],
ctx);
if (ret < 0)
@@ -1705,13 +1800,14 @@ static int sprint_nth_btf_arg(int idx, const char *type,
struct traceprobe_parse_context *ctx)
{
const char *name;
+ struct btf *btf = ctx_btf(ctx);
int ret;
if (idx >= ctx->nr_params) {
trace_probe_log_err(0, NO_BTFARG);
return -ENOENT;
}
- name = btf_name_by_offset(ctx->btf, ctx->params[idx].name_off);
+ name = btf_name_by_offset(btf, ctx->params[idx].name_off);
if (!name) {
trace_probe_log_err(0, NO_BTF_ENTRY);
return -ENOENT;
diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
index 262d8707a3df..6735b8b2432b 100644
--- a/kernel/trace/trace_probe.h
+++ b/kernel/trace/trace_probe.h
@@ -394,6 +394,7 @@ static inline int traceprobe_get_entry_data_size(struct
trace_probe *tp)
* TPARG_FL_KERNEL and TPARG_FL_USER are also mutually exclusive.
* TPARG_FL_FPROBE and TPARG_FL_TPOINT are optional but it should be with
* TPARG_FL_KERNEL.
+ * TPARG_FL_TYPECAST is set if an argument was typecast to a structure.
*/
#define TPARG_FL_RETURN BIT(0)
#define TPARG_FL_KERNEL BIT(1)
@@ -402,6 +403,7 @@ static inline int traceprobe_get_entry_data_size(struct
trace_probe *tp)
#define TPARG_FL_USER BIT(4)
#define TPARG_FL_FPROBE BIT(5)
#define TPARG_FL_TPOINT BIT(6)
+#define TPARG_FL_TYPECAST BIT(7)
#define TPARG_FL_LOC_MASK GENMASK(4, 0)
static inline bool tparg_is_function_entry(unsigned int flags)
@@ -422,7 +424,9 @@ struct traceprobe_parse_context {
const struct btf_param *params; /* Parameter of the function */
s32 nr_params; /* The number of the parameters */
struct btf *btf; /* The BTF to be used */
+ struct btf *struct_btf; /* The BTF to be used for structs */
const struct btf_type *last_type; /* Saved type */
+ const struct btf_type *last_struct; /* Saved structure */
u32 last_bitoffs; /* Saved bitoffs */
u32 last_bitsize; /* Saved bitsize */
struct trace_probe *tp;
--
2.53.0
