[PATCH v4] tracing/probes: Allow use of BTF names to dereference pointers

[PATCH v4] tracing/probes: Allow use of BTF names to dereference pointers

[Steven Rostedt]

From: Steven Rostedt <rostedt@goodmis.org>

Add syntax to the FETCHARGS parsing of probes to be able to typecast a
value to 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, unless the member is a function parameter that BTF already has
information about what structure the argument is pointing to.

But for event probes, or generic kprobes that records a register that
happens to be a pointer to a structure, they 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]*)(VAR)->FIELD[->FIELD..]

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
Changes since v3: https://patch.msgid.link/20260518095832.52659a3a@gandalf.local.home

 *** COMPLETE REWRITE FROM V3 ***

- Rewrote it to use typecasting instead of simply replacing BTF names with
  offsets.

 Documentation/trace/kprobetrace.rst |   3 +
 kernel/trace/trace_probe.c          | 110 ++++++++++++++++++++++++----
 kernel/trace/trace_probe.h          |   3 +
 3 files changed, 100 insertions(+), 16 deletions(-)

diff --git a/Documentation/trace/kprobetrace.rst b/Documentation/trace/kprobetrace.rst
index 3b6791c17e9b..450ac646fe4c 100644
--- a/Documentation/trace/kprobetrace.rst
+++ b/Documentation/trace/kprobetrace.rst
@@ -54,6 +54,9 @@ Synopsis of kprobe_events
   $retval	: Fetch return value.(\*2)
   $comm		: Fetch current task comm.
   +|-[u]OFFS(FETCHARG) : Fetch memory at FETCHARG +|- OFFS address.(\*3)(\*4)
+  (STRUCT*)FETCHARG->FIELD[->FIELD] : If BTF is supported, typecast FETCHARG to
+                  a pointer to STRUCT and then derference the pointer defined by
+                  ->FIELD.
   \IMM		: Store an immediate value to the argument.
   NAME=FETCHARG : Set NAME as the argument name of FETCHARG.
   FETCHARG:TYPE : Set TYPE as the type of FETCHARG. Currently, basic types
diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index e0d3a0da26af..b0829eb1cb52 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -464,6 +464,26 @@ 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->btf) {
+		struct btf *btf;
+		id = bpf_find_btf_id(sname, BTF_KIND_STRUCT, &btf);
+		if (id < 0)
+			return -EINVAL;
+		ctx->btf = btf;
+	} else {
+		id = btf_find_by_name_kind(ctx->btf, sname, BTF_KIND_STRUCT);
+		if (id < 0)
+			return -EINVAL;
+	}
+
+	ctx->last_struct = btf_type_by_id(ctx->btf, id);
+	return 0;
+}
+
 static int query_btf_context(struct traceprobe_parse_context *ctx)
 {
 	const struct btf_param *param;
@@ -471,12 +491,12 @@ static int query_btf_context(struct traceprobe_parse_context *ctx)
 	struct btf *btf;
 	s32 nr;
 
-	if (ctx->btf)
-		return 0;
-
 	if (!ctx->funcname)
 		return -EINVAL;
 
+	if (ctx->btf)
+		return 0;
+
 	type = btf_find_func_proto(ctx->funcname, &btf);
 	if (!type)
 		return -ENOENT;
@@ -514,6 +534,7 @@ static void clear_btf_context(struct traceprobe_parse_context *ctx)
 		ctx->proto = NULL;
 		ctx->params = NULL;
 		ctx->nr_params = 0;
+		ctx->last_struct = NULL;
 	}
 }
 
@@ -554,22 +575,28 @@ 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_STRUCT;
 	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(ctx->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 {
@@ -635,12 +662,12 @@ static int parse_btf_arg(char *varname,
 {
 	struct fetch_insn *code = *pcode;
 	const struct btf_param *params;
-	const struct btf_type *type;
+	const struct btf_type *type = NULL;
 	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_STRUCT)))
 		return -EINVAL;
 
 	is_ptr = split_next_field(varname, &field, ctx);
@@ -704,11 +731,18 @@ static int parse_btf_arg(char *varname,
 			goto found;
 		}
 	}
+
+	if (ctx->flags & TPARG_FL_STRUCT) {
+		type = ctx->last_struct;
+		goto found;
+	}
+
 	trace_probe_log_err(ctx->offset, NO_BTFARG);
 	return -ENOENT;
 
 found:
-	type = btf_type_skip_modifiers(ctx->btf, tid, &tid);
+	if (!type)
+		type = btf_type_skip_modifiers(ctx->btf, tid, &tid);
 	if (!type) {
 		trace_probe_log_err(ctx->offset, BAD_BTF_TID);
 		return -EINVAL;
@@ -952,6 +986,12 @@ static int parse_probe_vars(char *orig_arg, const struct fetch_type *t,
 	int ret = 0;
 	int len;
 
+	if (ctx->flags & TPARG_FL_STRUCT) {
+		ret = parse_btf_arg(orig_arg, pcode, end, ctx);
+		if (ret < 0)
+			return ret;
+	}
+
 	if (ctx->flags & TPARG_FL_TEVENT) {
 		if (code->data)
 			return -EFAULT;
@@ -1231,6 +1271,43 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
 				code->op = FETCH_OP_IMM;
 		}
 		break;
+	case '(':
+		tmp = strrchr(arg, ')');
+		if (!tmp) {
+			trace_probe_log_err(ctx->offset + strlen(arg),
+					    DEREF_OPEN_BRACE);
+			return -EINVAL;
+		}
+
+		tmp--;
+		if (*tmp != '*') {
+			trace_probe_log_err(ctx->offset + (tmp - arg),
+					    NO_PTR_STRCT);
+			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_STRUCT;
+		tmp += 2;
+
+		if (*tmp != '$') {
+			trace_probe_log_err(ctx->offset + (tmp - arg),
+					    BAD_VAR);
+			return -EINVAL;
+		}
+
+		ctx->offset += tmp - arg;
+		ret = parse_probe_vars(tmp, type, pcode, end, ctx);
+		ctx->flags &= ~TPARG_FL_STRUCT;
+		ctx->last_struct = NULL;
+		break;
 	default:
 		if (isalpha(arg[0]) || arg[0] == '_') {	/* BTF variable */
 			if (!tparg_is_function_entry(ctx->flags) &&
@@ -1504,6 +1581,7 @@ 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)
diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
index 262d8707a3df..88ab9f6da591 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_STRUCT 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_STRUCT BIT(7)
 #define TPARG_FL_LOC_MASK	GENMASK(4, 0)
 
 static inline bool tparg_is_function_entry(unsigned int flags)
@@ -423,6 +425,7 @@ struct traceprobe_parse_context {
 	s32 nr_params;			/* The number of the parameters */
 	struct btf *btf;		/* The BTF to be used */
 	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

Re: [PATCH v4] tracing/probes: Allow use of BTF names to dereference pointers

[kernel test robot]

Hi Steven,

kernel test robot noticed the following build errors:

[auto build test ERROR on trace/for-next]
[also build test ERROR on linus/master v7.1-rc4 next-20260518]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Steven-Rostedt/tracing-probes-Allow-use-of-BTF-names-to-dereference-pointers/20260519-121930
base:   https://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace for-next
patch link:    https://lore.kernel.org/r/20260518232312.0c78f055%40gandalf.local.home
patch subject: [PATCH v4] tracing/probes: Allow use of BTF names to dereference pointers
config: sh-defconfig (https://download.01.org/0day-ci/archive/20260519/202605191710.jVjifK67-lkp@intel.com/config)
compiler: sh4-linux-gcc (GCC) 15.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260519/202605191710.jVjifK67-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202605191710.jVjifK67-lkp@intel.com/

All errors (new ones prefixed by >>):

   kernel/trace/trace_probe.c: In function 'parse_probe_arg':
>> kernel/trace/trace_probe.c:1289:23: error: implicit declaration of function 'query_btf_struct' [-Wimplicit-function-declaration]
    1289 |                 ret = query_btf_struct(arg + 1, ctx);
         |                       ^~~~~~~~~~~~~~~~


vim +/query_btf_struct +1289 kernel/trace/trace_probe.c

  1120	
  1121	/* Recursive argument parser */
  1122	static int
  1123	parse_probe_arg(char *arg, const struct fetch_type *type,
  1124			struct fetch_insn **pcode, struct fetch_insn *end,
  1125			struct traceprobe_parse_context *ctx)
  1126	{
  1127		struct fetch_insn *code = *pcode;
  1128		unsigned long param;
  1129		int deref = FETCH_OP_DEREF;
  1130		long offset = 0;
  1131		char *tmp;
  1132		int ret = 0;
  1133	
  1134		switch (arg[0]) {
  1135		case '$':
  1136			ret = parse_probe_vars(arg, type, pcode, end, ctx);
  1137			break;
  1138	
  1139		case '%':	/* named register */
  1140			if (ctx->flags & (TPARG_FL_TEVENT | TPARG_FL_FPROBE)) {
  1141				/* eprobe and fprobe do not handle registers */
  1142				trace_probe_log_err(ctx->offset, BAD_VAR);
  1143				break;
  1144			}
  1145			ret = regs_query_register_offset(arg + 1);
  1146			if (ret >= 0) {
  1147				code->op = FETCH_OP_REG;
  1148				code->param = (unsigned int)ret;
  1149				ret = 0;
  1150			} else
  1151				trace_probe_log_err(ctx->offset, BAD_REG_NAME);
  1152			break;
  1153	
  1154		case '@':	/* memory, file-offset or symbol */
  1155			if (isdigit(arg[1])) {
  1156				ret = kstrtoul(arg + 1, 0, &param);
  1157				if (ret) {
  1158					trace_probe_log_err(ctx->offset, BAD_MEM_ADDR);
  1159					break;
  1160				}
  1161				/* load address */
  1162				code->op = FETCH_OP_IMM;
  1163				code->immediate = param;
  1164			} else if (arg[1] == '+') {
  1165				/* kprobes don't support file offsets */
  1166				if (ctx->flags & TPARG_FL_KERNEL) {
  1167					trace_probe_log_err(ctx->offset, FILE_ON_KPROBE);
  1168					return -EINVAL;
  1169				}
  1170				ret = kstrtol(arg + 2, 0, &offset);
  1171				if (ret) {
  1172					trace_probe_log_err(ctx->offset, BAD_FILE_OFFS);
  1173					break;
  1174				}
  1175	
  1176				code->op = FETCH_OP_FOFFS;
  1177				code->immediate = (unsigned long)offset;  // imm64?
  1178			} else {
  1179				/* uprobes don't support symbols */
  1180				if (!(ctx->flags & TPARG_FL_KERNEL)) {
  1181					trace_probe_log_err(ctx->offset, SYM_ON_UPROBE);
  1182					return -EINVAL;
  1183				}
  1184				/* Preserve symbol for updating */
  1185				code->op = FETCH_NOP_SYMBOL;
  1186				code->data = kstrdup(arg + 1, GFP_KERNEL);
  1187				if (!code->data)
  1188					return -ENOMEM;
  1189				if (++code == end) {
  1190					trace_probe_log_err(ctx->offset, TOO_MANY_OPS);
  1191					return -EINVAL;
  1192				}
  1193				code->op = FETCH_OP_IMM;
  1194				code->immediate = 0;
  1195			}
  1196			/* These are fetching from memory */
  1197			if (++code == end) {
  1198				trace_probe_log_err(ctx->offset, TOO_MANY_OPS);
  1199				return -EINVAL;
  1200			}
  1201			*pcode = code;
  1202			code->op = FETCH_OP_DEREF;
  1203			code->offset = offset;
  1204			break;
  1205	
  1206		case '+':	/* deref memory */
  1207		case '-':
  1208			if (arg[1] == 'u') {
  1209				deref = FETCH_OP_UDEREF;
  1210				arg[1] = arg[0];
  1211				arg++;
  1212			}
  1213			if (arg[0] == '+')
  1214				arg++;	/* Skip '+', because kstrtol() rejects it. */
  1215			tmp = strchr(arg, '(');
  1216			if (!tmp) {
  1217				trace_probe_log_err(ctx->offset, DEREF_NEED_BRACE);
  1218				return -EINVAL;
  1219			}
  1220			*tmp = '\0';
  1221			ret = kstrtol(arg, 0, &offset);
  1222			if (ret) {
  1223				trace_probe_log_err(ctx->offset, BAD_DEREF_OFFS);
  1224				break;
  1225			}
  1226			ctx->offset += (tmp + 1 - arg) + (arg[0] != '-' ? 1 : 0);
  1227			arg = tmp + 1;
  1228			tmp = strrchr(arg, ')');
  1229			if (!tmp) {
  1230				trace_probe_log_err(ctx->offset + strlen(arg),
  1231						    DEREF_OPEN_BRACE);
  1232				return -EINVAL;
  1233			} else {
  1234				const struct fetch_type *t2 = find_fetch_type(NULL, ctx->flags);
  1235				int cur_offs = ctx->offset;
  1236	
  1237				*tmp = '\0';
  1238				ret = parse_probe_arg(arg, t2, &code, end, ctx);
  1239				if (ret)
  1240					break;
  1241				ctx->offset = cur_offs;
  1242				if (code->op == FETCH_OP_COMM ||
  1243				    code->op == FETCH_OP_DATA) {
  1244					trace_probe_log_err(ctx->offset, COMM_CANT_DEREF);
  1245					return -EINVAL;
  1246				}
  1247				if (++code == end) {
  1248					trace_probe_log_err(ctx->offset, TOO_MANY_OPS);
  1249					return -EINVAL;
  1250				}
  1251				*pcode = code;
  1252	
  1253				code->op = deref;
  1254				code->offset = offset;
  1255				/* Reset the last type if used */
  1256				ctx->last_type = NULL;
  1257			}
  1258			break;
  1259		case '\\':	/* Immediate value */
  1260			if (arg[1] == '"') {	/* Immediate string */
  1261				ret = __parse_imm_string(arg + 2, &tmp, ctx->offset + 2);
  1262				if (ret)
  1263					break;
  1264				code->op = FETCH_OP_DATA;
  1265				code->data = tmp;
  1266			} else {
  1267				ret = str_to_immediate(arg + 1, &code->immediate);
  1268				if (ret)
  1269					trace_probe_log_err(ctx->offset + 1, BAD_IMM);
  1270				else
  1271					code->op = FETCH_OP_IMM;
  1272			}
  1273			break;
  1274		case '(':
  1275			tmp = strrchr(arg, ')');
  1276			if (!tmp) {
  1277				trace_probe_log_err(ctx->offset + strlen(arg),
  1278						    DEREF_OPEN_BRACE);
  1279				return -EINVAL;
  1280			}
  1281	
  1282			tmp--;
  1283			if (*tmp != '*') {
  1284				trace_probe_log_err(ctx->offset + (tmp - arg),
  1285						    NO_PTR_STRCT);
  1286				return -EINVAL;
  1287			}
  1288			*tmp = '\0';
> 1289			ret = query_btf_struct(arg + 1, ctx);
  1290			*tmp = '*';
  1291	
  1292			if (ret < 0) {
  1293				trace_probe_log_err(ctx->offset + 1, NO_PTR_STRCT);
  1294				return -EINVAL;
  1295			}
  1296	
  1297			ctx->flags |= TPARG_FL_STRUCT;
  1298			tmp += 2;
  1299	
  1300			if (*tmp != '$') {
  1301				trace_probe_log_err(ctx->offset + (tmp - arg),
  1302						    BAD_VAR);
  1303				return -EINVAL;
  1304			}
  1305	
  1306			ctx->offset += tmp - arg;
  1307			ret = parse_probe_vars(tmp, type, pcode, end, ctx);
  1308			ctx->flags &= ~TPARG_FL_STRUCT;
  1309			ctx->last_struct = NULL;
  1310			break;
  1311		default:
  1312			if (isalpha(arg[0]) || arg[0] == '_') {	/* BTF variable */
  1313				if (!tparg_is_function_entry(ctx->flags) &&
  1314				    !tparg_is_function_return(ctx->flags)) {
  1315					trace_probe_log_err(ctx->offset, NOSUP_BTFARG);
  1316					return -EINVAL;
  1317				}
  1318				ret = parse_btf_arg(arg, pcode, end, ctx);
  1319				break;
  1320			}
  1321		}
  1322		if (!ret && code->op == FETCH_OP_NOP) {
  1323			/* Parsed, but do not find fetch method */
  1324			trace_probe_log_err(ctx->offset, BAD_FETCH_ARG);
  1325			ret = -EINVAL;
  1326		}
  1327		return ret;
  1328	}
  1329	

--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH v4] tracing/probes: Allow use of BTF names to dereference pointers

[Masami Hiramatsu]

On Mon, 18 May 2026 23:23:12 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> From: Steven Rostedt <rostedt@goodmis.org>
> 
> Add syntax to the FETCHARGS parsing of probes to be able to typecast a
> value to 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, unless the member is a function parameter that BTF already has
> information about what structure the argument is pointing to.
> 
> But for event probes, or generic kprobes that records a register that
> happens to be a pointer to a structure, they cannot dereference these
> values with BTF naming, but must use numerical offsets.

Thanks for updating!

> 
> 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

Ah, eprobes supports "$PARAM" to access its parameter by name.
That is a bit complicated. Should we allow user to access
parameter without '$' prefix for eprobes?

>   # 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"

Looks very nice!

> 
> The syntax is simply: ([STRUCT]*)(VAR)->FIELD[->FIELD..]

Is the STRUCT optional?? (because [] means optional.) I guess no.

I think we maybe possible to skip '*' (Or, make it optional)
because this is not C-like typecasting, we don't support "struct"
reserved word, and it does not support white-spaces in each
fetcharg. In this case, (STRUCT)VAR->FIELD should work.

BTW, I'm also considering to support new cast syntax, which allows
us to derefer a pointer with "container_of". This is typically
used in the kernel.

We usually see this pattern:

struct {
	unsigned long		data;
	struct list_head	list;
} foo;

void callback(struct list_head *foo_list)
{
	unsigned long data = container_of(foo_list, struct foo, list)->data;
	...
}

To access @data, simple casting does not work. Thus we need a
new syntax:

	(STRUCT)(PTR,ASSIGN)->FIELD

So the above case, we can do:

	data=(foo)(foo_list,list)->data

This is naturally extend the type casting to support container_of()
equivalent casting.

> 
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
> Changes since v3: https://patch.msgid.link/20260518095832.52659a3a@gandalf.local.home
> 
>  *** COMPLETE REWRITE FROM V3 ***
> 
> - Rewrote it to use typecasting instead of simply replacing BTF names with
>   offsets.
> 
>  Documentation/trace/kprobetrace.rst |   3 +
>  kernel/trace/trace_probe.c          | 110 ++++++++++++++++++++++++----
>  kernel/trace/trace_probe.h          |   3 +
>  3 files changed, 100 insertions(+), 16 deletions(-)
> 
> diff --git a/Documentation/trace/kprobetrace.rst b/Documentation/trace/kprobetrace.rst
> index 3b6791c17e9b..450ac646fe4c 100644
> --- a/Documentation/trace/kprobetrace.rst
> +++ b/Documentation/trace/kprobetrace.rst
> @@ -54,6 +54,9 @@ Synopsis of kprobe_events
>    $retval	: Fetch return value.(\*2)
>    $comm		: Fetch current task comm.
>    +|-[u]OFFS(FETCHARG) : Fetch memory at FETCHARG +|- OFFS address.(\*3)(\*4)
> +  (STRUCT*)FETCHARG->FIELD[->FIELD] : If BTF is supported, typecast FETCHARG to
> +                  a pointer to STRUCT and then derference the pointer defined by
> +                  ->FIELD.
>    \IMM		: Store an immediate value to the argument.
>    NAME=FETCHARG : Set NAME as the argument name of FETCHARG.
>    FETCHARG:TYPE : Set TYPE as the type of FETCHARG. Currently, basic types
> diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> index e0d3a0da26af..b0829eb1cb52 100644
> --- a/kernel/trace/trace_probe.c
> +++ b/kernel/trace/trace_probe.c
> @@ -464,6 +464,26 @@ 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->btf) {
> +		struct btf *btf;

This needs an empty line here.

> +		id = bpf_find_btf_id(sname, BTF_KIND_STRUCT, &btf);
> +		if (id < 0)
> +			return -EINVAL;

Why don't you return id (it has corresponding errno)?

> +		ctx->btf = btf;
> +	} else {
> +		id = btf_find_by_name_kind(ctx->btf, sname, BTF_KIND_STRUCT);
> +		if (id < 0)
> +			return -EINVAL;

Ditto.

> +	}
> +
> +	ctx->last_struct = btf_type_by_id(ctx->btf, id);
> +	return 0;
> +}
> +
>  static int query_btf_context(struct traceprobe_parse_context *ctx)
>  {
>  	const struct btf_param *param;
> @@ -471,12 +491,12 @@ static int query_btf_context(struct traceprobe_parse_context *ctx)
>  	struct btf *btf;
>  	s32 nr;
>  
> -	if (ctx->btf)
> -		return 0;
> -
>  	if (!ctx->funcname)
>  		return -EINVAL;
>  
> +	if (ctx->btf)
> +		return 0;
> +

Could you tell me why this order is changed?
I think this type casting will allow us to skip checking funcname
because btf context is already specified.

Ah, BTW, we may need to use a special struct btf* for type
casting. If the target function is in a module and the
casting type is defined in vmlinux, those are stored in
the different places...


for example,

 p funcA (foo)$arg1->bar buz

In this case, buz needs to use BTF including funcA.
Maybe we need to introduce ctx->func_btf, which resets ctx->btf
in traceprobe_parse_probe_arg_body() where parse_probe_arg()
is calling, e.g.

	ctx->last_type = NULL;
+	if (ctx->btf)
+		btf_put(ctx->btf);
+	ctx->btf = ctx->func_btf;
	ret = parse_probe_arg(arg, parg->type, &code, &code[FETCH_INSN_MAX - 1],
			      ctx);


>  	type = btf_find_func_proto(ctx->funcname, &btf);
>  	if (!type)
>  		return -ENOENT;
> @@ -514,6 +534,7 @@ static void clear_btf_context(struct traceprobe_parse_context *ctx)
>  		ctx->proto = NULL;
>  		ctx->params = NULL;
>  		ctx->nr_params = 0;
> +		ctx->last_struct = NULL;
>  	}
>  }
>  
> @@ -554,22 +575,28 @@ 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_STRUCT;
>  	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(ctx->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 {
> @@ -635,12 +662,12 @@ static int parse_btf_arg(char *varname,
>  {
>  	struct fetch_insn *code = *pcode;
>  	const struct btf_param *params;
> -	const struct btf_type *type;
> +	const struct btf_type *type = NULL;
>  	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_STRUCT)))
>  		return -EINVAL;
>  
>  	is_ptr = split_next_field(varname, &field, ctx);
> @@ -704,11 +731,18 @@ static int parse_btf_arg(char *varname,
>  			goto found;
>  		}
>  	}
> +
> +	if (ctx->flags & TPARG_FL_STRUCT) {
> +		type = ctx->last_struct;
> +		goto found;

I rather like to jump type_found: label instead of
checking !type. (Or, save tid instead of type)

> +	}
> +
>  	trace_probe_log_err(ctx->offset, NO_BTFARG);
>  	return -ENOENT;
>  
>  found:
> -	type = btf_type_skip_modifiers(ctx->btf, tid, &tid);
> +	if (!type)
> +		type = btf_type_skip_modifiers(ctx->btf, tid, &tid);

type_found:

>  	if (!type) {
>  		trace_probe_log_err(ctx->offset, BAD_BTF_TID);
>  		return -EINVAL;
> @@ -952,6 +986,12 @@ static int parse_probe_vars(char *orig_arg, const struct fetch_type *t,
>  	int ret = 0;
>  	int len;
>  
> +	if (ctx->flags & TPARG_FL_STRUCT) {
> +		ret = parse_btf_arg(orig_arg, pcode, end, ctx);
> +		if (ret < 0)
> +			return ret;
> +	}
> +
>  	if (ctx->flags & TPARG_FL_TEVENT) {
>  		if (code->data)
>  			return -EFAULT;
> @@ -1231,6 +1271,43 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
>  				code->op = FETCH_OP_IMM;
>  		}
>  		break;
> +	case '(':
> +		tmp = strrchr(arg, ')');

OK, in this step, we don't support nested cast etc. so this works.

> +		if (!tmp) {
> +			trace_probe_log_err(ctx->offset + strlen(arg),
> +					    DEREF_OPEN_BRACE);
> +			return -EINVAL;
> +		}
> +
> +		tmp--;
> +		if (*tmp != '*') {
> +			trace_probe_log_err(ctx->offset + (tmp - arg),
> +					    NO_PTR_STRCT);
> +			return -EINVAL;
> +		}

So I think this can be optional, not an error.

> +		*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_STRUCT;
> +		tmp += 2;
> +
> +		if (*tmp != '$') {
> +			trace_probe_log_err(ctx->offset + (tmp - arg),
> +					    BAD_VAR);
> +			return -EINVAL;
> +		}

Ok, this limitation will be removed afterwards.

Thanks,

> +
> +		ctx->offset += tmp - arg;
> +		ret = parse_probe_vars(tmp, type, pcode, end, ctx);
> +		ctx->flags &= ~TPARG_FL_STRUCT;
> +		ctx->last_struct = NULL;
> +		break;
>  	default:
>  		if (isalpha(arg[0]) || arg[0] == '_') {	/* BTF variable */
>  			if (!tparg_is_function_entry(ctx->flags) &&
> @@ -1504,6 +1581,7 @@ 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)
> diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
> index 262d8707a3df..88ab9f6da591 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_STRUCT 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_STRUCT BIT(7)
>  #define TPARG_FL_LOC_MASK	GENMASK(4, 0)
>  
>  static inline bool tparg_is_function_entry(unsigned int flags)
> @@ -423,6 +425,7 @@ struct traceprobe_parse_context {
>  	s32 nr_params;			/* The number of the parameters */
>  	struct btf *btf;		/* The BTF to be used */
>  	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
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>

Re: [PATCH v4] tracing/probes: Allow use of BTF names to dereference pointers

[kernel test robot]

Hi Steven,

kernel test robot noticed the following build errors:

[auto build test ERROR on trace/for-next]
[also build test ERROR on linus/master v7.1-rc4 next-20260518]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Steven-Rostedt/tracing-probes-Allow-use-of-BTF-names-to-dereference-pointers/20260519-121930
base:   https://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace for-next
patch link:    https://lore.kernel.org/r/20260518232312.0c78f055%40gandalf.local.home
patch subject: [PATCH v4] tracing/probes: Allow use of BTF names to dereference pointers
config: sparc64-defconfig (https://download.01.org/0day-ci/archive/20260519/202605191828.Y3E73pH1-lkp@intel.com/config)
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260519/202605191828.Y3E73pH1-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202605191828.Y3E73pH1-lkp@intel.com/

All errors (new ones prefixed by >>):

>> kernel/trace/trace_probe.c:1289:9: error: call to undeclared function 'query_btf_struct'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
    1289 |                 ret = query_btf_struct(arg + 1, ctx);
         |                       ^
   1 error generated.


vim +/query_btf_struct +1289 kernel/trace/trace_probe.c

  1120	
  1121	/* Recursive argument parser */
  1122	static int
  1123	parse_probe_arg(char *arg, const struct fetch_type *type,
  1124			struct fetch_insn **pcode, struct fetch_insn *end,
  1125			struct traceprobe_parse_context *ctx)
  1126	{
  1127		struct fetch_insn *code = *pcode;
  1128		unsigned long param;
  1129		int deref = FETCH_OP_DEREF;
  1130		long offset = 0;
  1131		char *tmp;
  1132		int ret = 0;
  1133	
  1134		switch (arg[0]) {
  1135		case '$':
  1136			ret = parse_probe_vars(arg, type, pcode, end, ctx);
  1137			break;
  1138	
  1139		case '%':	/* named register */
  1140			if (ctx->flags & (TPARG_FL_TEVENT | TPARG_FL_FPROBE)) {
  1141				/* eprobe and fprobe do not handle registers */
  1142				trace_probe_log_err(ctx->offset, BAD_VAR);
  1143				break;
  1144			}
  1145			ret = regs_query_register_offset(arg + 1);
  1146			if (ret >= 0) {
  1147				code->op = FETCH_OP_REG;
  1148				code->param = (unsigned int)ret;
  1149				ret = 0;
  1150			} else
  1151				trace_probe_log_err(ctx->offset, BAD_REG_NAME);
  1152			break;
  1153	
  1154		case '@':	/* memory, file-offset or symbol */
  1155			if (isdigit(arg[1])) {
  1156				ret = kstrtoul(arg + 1, 0, &param);
  1157				if (ret) {
  1158					trace_probe_log_err(ctx->offset, BAD_MEM_ADDR);
  1159					break;
  1160				}
  1161				/* load address */
  1162				code->op = FETCH_OP_IMM;
  1163				code->immediate = param;
  1164			} else if (arg[1] == '+') {
  1165				/* kprobes don't support file offsets */
  1166				if (ctx->flags & TPARG_FL_KERNEL) {
  1167					trace_probe_log_err(ctx->offset, FILE_ON_KPROBE);
  1168					return -EINVAL;
  1169				}
  1170				ret = kstrtol(arg + 2, 0, &offset);
  1171				if (ret) {
  1172					trace_probe_log_err(ctx->offset, BAD_FILE_OFFS);
  1173					break;
  1174				}
  1175	
  1176				code->op = FETCH_OP_FOFFS;
  1177				code->immediate = (unsigned long)offset;  // imm64?
  1178			} else {
  1179				/* uprobes don't support symbols */
  1180				if (!(ctx->flags & TPARG_FL_KERNEL)) {
  1181					trace_probe_log_err(ctx->offset, SYM_ON_UPROBE);
  1182					return -EINVAL;
  1183				}
  1184				/* Preserve symbol for updating */
  1185				code->op = FETCH_NOP_SYMBOL;
  1186				code->data = kstrdup(arg + 1, GFP_KERNEL);
  1187				if (!code->data)
  1188					return -ENOMEM;
  1189				if (++code == end) {
  1190					trace_probe_log_err(ctx->offset, TOO_MANY_OPS);
  1191					return -EINVAL;
  1192				}
  1193				code->op = FETCH_OP_IMM;
  1194				code->immediate = 0;
  1195			}
  1196			/* These are fetching from memory */
  1197			if (++code == end) {
  1198				trace_probe_log_err(ctx->offset, TOO_MANY_OPS);
  1199				return -EINVAL;
  1200			}
  1201			*pcode = code;
  1202			code->op = FETCH_OP_DEREF;
  1203			code->offset = offset;
  1204			break;
  1205	
  1206		case '+':	/* deref memory */
  1207		case '-':
  1208			if (arg[1] == 'u') {
  1209				deref = FETCH_OP_UDEREF;
  1210				arg[1] = arg[0];
  1211				arg++;
  1212			}
  1213			if (arg[0] == '+')
  1214				arg++;	/* Skip '+', because kstrtol() rejects it. */
  1215			tmp = strchr(arg, '(');
  1216			if (!tmp) {
  1217				trace_probe_log_err(ctx->offset, DEREF_NEED_BRACE);
  1218				return -EINVAL;
  1219			}
  1220			*tmp = '\0';
  1221			ret = kstrtol(arg, 0, &offset);
  1222			if (ret) {
  1223				trace_probe_log_err(ctx->offset, BAD_DEREF_OFFS);
  1224				break;
  1225			}
  1226			ctx->offset += (tmp + 1 - arg) + (arg[0] != '-' ? 1 : 0);
  1227			arg = tmp + 1;
  1228			tmp = strrchr(arg, ')');
  1229			if (!tmp) {
  1230				trace_probe_log_err(ctx->offset + strlen(arg),
  1231						    DEREF_OPEN_BRACE);
  1232				return -EINVAL;
  1233			} else {
  1234				const struct fetch_type *t2 = find_fetch_type(NULL, ctx->flags);
  1235				int cur_offs = ctx->offset;
  1236	
  1237				*tmp = '\0';
  1238				ret = parse_probe_arg(arg, t2, &code, end, ctx);
  1239				if (ret)
  1240					break;
  1241				ctx->offset = cur_offs;
  1242				if (code->op == FETCH_OP_COMM ||
  1243				    code->op == FETCH_OP_DATA) {
  1244					trace_probe_log_err(ctx->offset, COMM_CANT_DEREF);
  1245					return -EINVAL;
  1246				}
  1247				if (++code == end) {
  1248					trace_probe_log_err(ctx->offset, TOO_MANY_OPS);
  1249					return -EINVAL;
  1250				}
  1251				*pcode = code;
  1252	
  1253				code->op = deref;
  1254				code->offset = offset;
  1255				/* Reset the last type if used */
  1256				ctx->last_type = NULL;
  1257			}
  1258			break;
  1259		case '\\':	/* Immediate value */
  1260			if (arg[1] == '"') {	/* Immediate string */
  1261				ret = __parse_imm_string(arg + 2, &tmp, ctx->offset + 2);
  1262				if (ret)
  1263					break;
  1264				code->op = FETCH_OP_DATA;
  1265				code->data = tmp;
  1266			} else {
  1267				ret = str_to_immediate(arg + 1, &code->immediate);
  1268				if (ret)
  1269					trace_probe_log_err(ctx->offset + 1, BAD_IMM);
  1270				else
  1271					code->op = FETCH_OP_IMM;
  1272			}
  1273			break;
  1274		case '(':
  1275			tmp = strrchr(arg, ')');
  1276			if (!tmp) {
  1277				trace_probe_log_err(ctx->offset + strlen(arg),
  1278						    DEREF_OPEN_BRACE);
  1279				return -EINVAL;
  1280			}
  1281	
  1282			tmp--;
  1283			if (*tmp != '*') {
  1284				trace_probe_log_err(ctx->offset + (tmp - arg),
  1285						    NO_PTR_STRCT);
  1286				return -EINVAL;
  1287			}
  1288			*tmp = '\0';
> 1289			ret = query_btf_struct(arg + 1, ctx);
  1290			*tmp = '*';
  1291	
  1292			if (ret < 0) {
  1293				trace_probe_log_err(ctx->offset + 1, NO_PTR_STRCT);
  1294				return -EINVAL;
  1295			}
  1296	
  1297			ctx->flags |= TPARG_FL_STRUCT;
  1298			tmp += 2;
  1299	
  1300			if (*tmp != '$') {
  1301				trace_probe_log_err(ctx->offset + (tmp - arg),
  1302						    BAD_VAR);
  1303				return -EINVAL;
  1304			}
  1305	
  1306			ctx->offset += tmp - arg;
  1307			ret = parse_probe_vars(tmp, type, pcode, end, ctx);
  1308			ctx->flags &= ~TPARG_FL_STRUCT;
  1309			ctx->last_struct = NULL;
  1310			break;
  1311		default:
  1312			if (isalpha(arg[0]) || arg[0] == '_') {	/* BTF variable */
  1313				if (!tparg_is_function_entry(ctx->flags) &&
  1314				    !tparg_is_function_return(ctx->flags)) {
  1315					trace_probe_log_err(ctx->offset, NOSUP_BTFARG);
  1316					return -EINVAL;
  1317				}
  1318				ret = parse_btf_arg(arg, pcode, end, ctx);
  1319				break;
  1320			}
  1321		}
  1322		if (!ret && code->op == FETCH_OP_NOP) {
  1323			/* Parsed, but do not find fetch method */
  1324			trace_probe_log_err(ctx->offset, BAD_FETCH_ARG);
  1325			ret = -EINVAL;
  1326		}
  1327		return ret;
  1328	}
  1329	

--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki