tracing/probes: Support BTF based data structure field access

Using BTF to access the fields of a data structure. You can use this
for accessing the field with '->' or '.' operation with BTF argument.

 # echo 't sched_switch next=next->pid vruntime=next->se.vruntime' \
   > dynamic_events
 # echo 1 > events/tracepoints/sched_switch/enable
 # head -n 40 trace | tail
          <idle>-0       [000] d..3.   272.565382: sched_switch: (__probestub_sched_switch+0x4/0x10) next=26 vruntime=956533179
      kcompactd0-26      [000] d..3.   272.565406: sched_switch: (__probestub_sched_switch+0x4/0x10) next=0 vruntime=0
          <idle>-0       [000] d..3.   273.069441: sched_switch: (__probestub_sched_switch+0x4/0x10) next=9 vruntime=956533179
     kworker/0:1-9       [000] d..3.   273.069464: sched_switch: (__probestub_sched_switch+0x4/0x10) next=26 vruntime=956579181
      kcompactd0-26      [000] d..3.   273.069480: sched_switch: (__probestub_sched_switch+0x4/0x10) next=0 vruntime=0
          <idle>-0       [000] d..3.   273.141434: sched_switch: (__probestub_sched_switch+0x4/0x10) next=22 vruntime=956533179
    kworker/u2:1-22      [000] d..3.   273.141461: sched_switch: (__probestub_sched_switch+0x4/0x10) next=0 vruntime=0
          <idle>-0       [000] d..3.   273.480872: sched_switch: (__probestub_sched_switch+0x4/0x10) next=22 vruntime=956585857
    kworker/u2:1-22      [000] d..3.   273.480905: sched_switch: (__probestub_sched_switch+0x4/0x10) next=70 vruntime=959533179
              sh-70      [000] d..3.   273.481102: sched_switch: (__probestub_sched_switch+0x4/0x10) next=0 vruntime=0

Link: https://lore.kernel.org/all/169272157251.160970.9318175874130965571.stgit@devnote2/

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>

kernel/trace/trace.c

@@ -5717,7 +5717,8 @@ static const char readme_msg[] =
 	"\t fetcharg: (%<register>|$<efield>), @<address>, @<symbol>[+|-<offset>],\n"
 #ifdef CONFIG_HAVE_FUNCTION_ARG_ACCESS_API
 #ifdef CONFIG_PROBE_EVENTS_BTF_ARGS
-	"\t           $stack<index>, $stack, $retval, $comm, $arg<N>, <argname>\n"
+	"\t           $stack<index>, $stack, $retval, $comm, $arg<N>,\n"
+	"\t           <argname>[->field[->field|.field...]],\n"
 #else
 	"\t           $stack<index>, $stack, $retval, $comm, $arg<N>,\n"
 #endif

kernel/trace/trace_probe.c

@@ -310,16 +310,14 @@ static u32 btf_type_int(const struct btf_type *t)
 	return *(u32 *)(t + 1);
 }
 
-static const char *type_from_btf_id(struct btf *btf, s32 id)
+static const char *fetch_type_from_btf_type(struct btf *btf,
+					const struct btf_type *type,
+					struct traceprobe_parse_context *ctx)
 {
-	const struct btf_type *t;
 	u32 intdata;
-	s32 tid;
 
 	/* TODO: const char * could be converted as a string */
-	t = btf_type_skip_modifiers(btf, id, &tid);
+	switch (BTF_INFO_KIND(type->info)) {
-
-	switch (BTF_INFO_KIND(t->info)) {
 	case BTF_KIND_ENUM:
 		/* enum is "int", so convert to "s32" */
 		return "s32";
@@ -332,7 +330,7 @@ static const char *type_from_btf_id(struct btf *btf, s32 id)
 		else
 			return "x32";
 	case BTF_KIND_INT:
-		intdata = btf_type_int(t);
+		intdata = btf_type_int(type);
 		if (BTF_INT_ENCODING(intdata) & BTF_INT_SIGNED) {
 			switch (BTF_INT_BITS(intdata)) {
 			case 8:
@@ -355,6 +353,10 @@ static const char *type_from_btf_id(struct btf *btf, s32 id)
 			case 64:
 				return "u64";
 			}
+			/* bitfield, size is encoded in the type */
+			ctx->last_bitsize = BTF_INT_BITS(intdata);
+			ctx->last_bitoffs += BTF_INT_OFFSET(intdata);
+			return "u64";
 		}
 	}
 	/* TODO: support other types */
@@ -406,15 +408,136 @@ static void clear_btf_context(struct traceprobe_parse_context *ctx)
 	}
 }
 
-static int parse_btf_arg(const char *varname, struct fetch_insn *code,
+/* Return 1 if the field separater is arrow operator ('->') */
+static int split_next_field(char *varname, char **next_field,
+			    struct traceprobe_parse_context *ctx)
+{
+	char *field;
+	int ret = 0;
+
+	field = strpbrk(varname, ".-");
+	if (field) {
+		if (field[0] == '-' && field[1] == '>') {
+			field[0] = '\0';
+			field += 2;
+			ret = 1;
+		} else if (field[0] == '.') {
+			field[0] = '\0';
+			field += 1;
+		} else {
+			trace_probe_log_err(ctx->offset + field - varname, BAD_HYPHEN);
+			return -EINVAL;
+		}
+		*next_field = field;
+	}
+
+	return ret;
+}
+
+/*
+ * Parse the field of data structure. The @type must be a pointer type
+ * pointing the target data structure type.
+ */
+static int parse_btf_field(char *fieldname, const struct btf_type *type,
+			   struct fetch_insn **pcode, struct fetch_insn *end,
+			   struct traceprobe_parse_context *ctx)
+{
+	struct fetch_insn *code = *pcode;
+	const struct btf_member *field;
+	u32 bitoffs, anon_offs;
+	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;
+		}
+
+		bitoffs = 0;
+		do {
+			/* Inner loop for solving dot operator ('.') */
+			next = NULL;
+			is_ptr = split_next_field(fieldname, &next, ctx);
+			if (is_ptr < 0)
+				return is_ptr;
+
+			anon_offs = 0;
+			field = btf_find_struct_member(ctx->btf, type, fieldname,
+						       &anon_offs);
+			if (!field) {
+				trace_probe_log_err(ctx->offset, NO_BTF_FIELD);
+				return -ENOENT;
+			}
+			/* Add anonymous structure/union offset */
+			bitoffs += anon_offs;
+
+			/* Accumulate the bit-offsets of the dot-connected fields */
+			if (btf_type_kflag(type)) {
+				bitoffs += BTF_MEMBER_BIT_OFFSET(field->offset);
+				ctx->last_bitsize = BTF_MEMBER_BITFIELD_SIZE(field->offset);
+			} else {
+				bitoffs += field->offset;
+				ctx->last_bitsize = 0;
+			}
+
+			type = btf_type_skip_modifiers(ctx->btf, field->type, &tid);
+			if (!type) {
+				trace_probe_log_err(ctx->offset, BAD_BTF_TID);
+				return -EINVAL;
+			}
+
+			ctx->offset += next - fieldname;
+			fieldname = next;
+		} while (!is_ptr && fieldname);
+
+		if (++code == end) {
+			trace_probe_log_err(ctx->offset, TOO_MANY_OPS);
+			return -EINVAL;
+		}
+		code->op = FETCH_OP_DEREF;	/* TODO: user deref support */
+		code->offset = bitoffs / 8;
+		*pcode = code;
+
+		ctx->last_bitoffs = bitoffs % 8;
+		ctx->last_type = type;
+	} while (fieldname);
+
+	return 0;
+}
+
+static int parse_btf_arg(char *varname,
+			 struct fetch_insn **pcode, struct fetch_insn *end,
 			 struct traceprobe_parse_context *ctx)
 {
+	struct fetch_insn *code = *pcode;
 	const struct btf_param *params;
-	int i;
+	const struct btf_type *type;
+	char *field = NULL;
+	int i, is_ptr;
+	u32 tid;
 
 	if (WARN_ON_ONCE(!ctx->funcname))
 		return -EINVAL;
 
+	is_ptr = split_next_field(varname, &field, ctx);
+	if (is_ptr < 0)
+		return is_ptr;
+	if (!is_ptr && field) {
+		/* dot-connected field on an argument is not supported. */
+		trace_probe_log_err(ctx->offset + field - varname,
+				    NOSUP_DAT_ARG);
+		return -EOPNOTSUPP;
+	}
+
 	if (!ctx->params) {
 		params = find_btf_func_param(ctx->funcname,
 					     &ctx->nr_params, &ctx->btf,
@@ -436,24 +559,39 @@ static int parse_btf_arg(const char *varname, struct fetch_insn *code,
 				code->param = i + 1;
 			else
 				code->param = i;
-			return 0;
+
+			tid = params[i].type;
+			goto found;
 		}
 	}
 	trace_probe_log_err(ctx->offset, NO_BTFARG);
 	return -ENOENT;
+
+found:
+	type = btf_type_skip_modifiers(ctx->btf, tid, &tid);
+	if (!type) {
+		trace_probe_log_err(ctx->offset, BAD_BTF_TID);
+		return -EINVAL;
+	}
+	/* Initialize the last type information */
+	ctx->last_type = type;
+	ctx->last_bitoffs = 0;
+	ctx->last_bitsize = 0;
+	if (field) {
+		ctx->offset += field - varname;
+		return parse_btf_field(field, type, pcode, end, ctx);
+	}
+	return 0;
 }
 
-static const struct fetch_type *parse_btf_arg_type(int arg_idx,
+static const struct fetch_type *parse_btf_arg_type(
 					struct traceprobe_parse_context *ctx)
 {
 	struct btf *btf = ctx->btf;
 	const char *typestr = NULL;
 
-	if (btf && ctx->params) {
+	if (btf && ctx->last_type)
-		if (ctx->flags & TPARG_FL_TPOINT)
+		typestr = fetch_type_from_btf_type(btf, ctx->last_type, ctx);
-			arg_idx--;
-		typestr = type_from_btf_id(btf, ctx->params[arg_idx].type);
-	}
 
 	return find_fetch_type(typestr, ctx->flags);
 }
@@ -462,14 +600,16 @@ static const struct fetch_type *parse_btf_retval_type(
 					struct traceprobe_parse_context *ctx)
 {
 	const char *typestr = NULL;
-	const struct btf_type *t;
+	const struct btf_type *type;
 	struct btf *btf;
 
 	if (ctx->funcname) {
 		/* Do not use ctx->btf, because it must be used with ctx->param */
-		t = btf_find_func_proto(ctx->funcname, &btf);
+		type = btf_find_func_proto(ctx->funcname, &btf);
-		if (t) {
+		if (type) {
-			typestr = type_from_btf_id(btf, t->type);
+			type = btf_type_skip_modifiers(btf, type->type, NULL);
+			if (!IS_ERR_OR_NULL(type))
+				typestr = fetch_type_from_btf_type(btf, type, ctx);
 			btf_put(btf);
 		}
 	}
@@ -477,6 +617,28 @@ static const struct fetch_type *parse_btf_retval_type(
 	return find_fetch_type(typestr, ctx->flags);
 }
 
+static int parse_btf_bitfield(struct fetch_insn **pcode,
+			      struct traceprobe_parse_context *ctx)
+{
+	struct fetch_insn *code = *pcode;
+
+	if ((ctx->last_bitsize % 8 == 0) && ctx->last_bitoffs == 0)
+		return 0;
+
+	code++;
+	if (code->op != FETCH_OP_NOP) {
+		trace_probe_log_err(ctx->offset, TOO_MANY_OPS);
+		return -EINVAL;
+	}
+	*pcode = code;
+
+	code->op = FETCH_OP_MOD_BF;
+	code->lshift = 64 - (ctx->last_bitsize + ctx->last_bitoffs);
+	code->rshift = 64 - ctx->last_bitsize;
+	code->basesize = 64 / 8;
+	return 0;
+}
+
 static bool is_btf_retval_void(const char *funcname)
 {
 	const struct btf_type *t;
@@ -503,14 +665,22 @@ static const struct btf_param *find_btf_func_param(const char *funcname, s32 *nr
 	return ERR_PTR(-EOPNOTSUPP);
 }
 
-static int parse_btf_arg(const char *varname, struct fetch_insn *code,
+static int parse_btf_arg(char *varname,
+			 struct fetch_insn **pcode, struct fetch_insn *end,
 			 struct traceprobe_parse_context *ctx)
 {
 	trace_probe_log_err(ctx->offset, NOSUP_BTFARG);
 	return -EOPNOTSUPP;
 }
 
-#define parse_btf_arg_type(idx, ctx)		\
+static int parse_btf_bitfield(struct fetch_insn **pcode,
+			      struct traceprobe_parse_context *ctx)
+{
+	trace_probe_log_err(ctx->offset, NOSUP_BTFARG);
+	return -EOPNOTSUPP;
+}
+
+#define parse_btf_arg_type(ctx)		\
 	find_fetch_type(NULL, ctx->flags)
 
 #define parse_btf_retval_type(ctx)		\
@@ -778,6 +948,8 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
 
 			code->op = deref;
 			code->offset = offset;
+			/* Reset the last type if used */
+			ctx->last_type = NULL;
 		}
 		break;
 	case '\\':	/* Immediate value */
@@ -801,7 +973,7 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
 				trace_probe_log_err(ctx->offset, NOSUP_BTFARG);
 				return -EINVAL;
 			}
-			ret = parse_btf_arg(arg, code, ctx);
+			ret = parse_btf_arg(arg, pcode, end, ctx);
 			break;
 		}
 	}
@@ -947,6 +1119,7 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
 		goto out;
 	code[FETCH_INSN_MAX - 1].op = FETCH_OP_END;
 
+	ctx->last_type = NULL;
 	ret = parse_probe_arg(arg, parg->type, &code, &code[FETCH_INSN_MAX - 1],
 			      ctx);
 	if (ret)
@@ -954,9 +1127,9 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
 
 	/* Update storing type if BTF is available */
 	if (IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS) && !t) {
-		if (code->op == FETCH_OP_ARG)
+		if (ctx->last_type)
-			parg->type = parse_btf_arg_type(code->param, ctx);
+			parg->type = parse_btf_arg_type(ctx);
-		else if (code->op == FETCH_OP_RETVAL)
+		else if (ctx->flags & TPARG_FL_RETURN)
 			parg->type = parse_btf_retval_type(ctx);
 	}
 
@@ -1031,6 +1204,11 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
 			trace_probe_log_err(ctx->offset + t - arg, BAD_BITFIELD);
 			goto fail;
 		}
+	} else if (IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS) &&
+		   ctx->last_type) {
+		ret = parse_btf_bitfield(&code, ctx);
+		if (ret)
+			goto fail;
 	}
 	ret = -EINVAL;
 	/* Loop(Array) operation */

kernel/trace/trace_probe.h

@@ -388,6 +388,9 @@ 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 */
+	const struct btf_type *last_type;	/* Saved type */
+	u32 last_bitoffs;		/* Saved bitoffs */
+	u32 last_bitsize;		/* Saved bitsize */
 	unsigned int flags;
 	int offset;
 };
@@ -503,7 +506,13 @@ extern int traceprobe_define_arg_fields(struct trace_event_call *event_call,
 	C(BAD_VAR_ARGS,		"$arg* must be an independent parameter without name etc."),\
 	C(NOFENTRY_ARGS,	"$arg* can be used only on function entry"),	\
 	C(DOUBLE_ARGS,		"$arg* can be used only once in the parameters"),	\
-	C(ARGS_2LONG,		"$arg* failed because the argument list is too long"),
+	C(ARGS_2LONG,		"$arg* failed because the argument list is too long"),	\
+	C(ARGIDX_2BIG,		"$argN index is too big"),		\
+	C(NO_PTR_STRCT,		"This is not a pointer to union/structure."),	\
+	C(NOSUP_DAT_ARG,	"Non pointer structure/union argument is not supported."),\
+	C(BAD_HYPHEN,		"Failed to parse single hyphen. Forgot '>'?"),	\
+	C(NO_BTF_FIELD,		"This field is not found."),	\
+	C(BAD_BTF_TID,		"Failed to get BTF type info."),
 
 #undef C
 #define C(a, b)		TP_ERR_##a