Commit d157d769 authored by Masami Hiramatsu (Google)'s avatar Masami Hiramatsu (Google)
Browse files

tracing/probes: Support BTF field access from $retval 

Support BTF argument on '$retval' for function return events including
kretprobe and fprobe for accessing the return value.
This also allows user to access its fields if the return value is a
pointer of a data structure.

E.g.
 # echo 'f getname_flags%return +0($retval->name):string' \
   > dynamic_events
 # echo 1 > events/fprobes/getname_flags__exit/enable
 # ls > /dev/null
 # head -n 40 trace | tail
              ls-87      [000] ...1.  8067.616101: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./function_profile_enabled"
              ls-87      [000] ...1.  8067.616108: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./trace_stat"
              ls-87      [000] ...1.  8067.616115: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./set_graph_notrace"
              ls-87      [000] ...1.  8067.616122: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./set_graph_function"
              ls-87      [000] ...1.  8067.616129: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./set_ftrace_notrace"
              ls-87      [000] ...1.  8067.616135: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./set_ftrace_filter"
              ls-87      [000] ...1.  8067.616143: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./touched_functions"
              ls-87      [000] ...1.  8067.616237: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./enabled_functions"
              ls-87      [000] ...1.  8067.616245: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./available_filter_functions"
              ls-87      [000] ...1.  8067.616253: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./set_ftrace_notrace_pid"


Link: https://lore.kernel.org/all/169272158234.160970.2446691104240645205.stgit@devnote2/



Signed-off-by: default avatarMasami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent c440adfb

kernel/trace/trace_probe.c

+85 −102
Original line number Diff line number Diff line
@@ -364,38 +364,46 @@ static const char *fetch_type_from_btf_type(struct btf *btf, 
	return NULL;

}



static const struct btf_param *find_btf_func_param(const char *funcname, s32 *nr,

						   struct btf **btf_p, bool tracepoint)

static int query_btf_context(struct traceprobe_parse_context *ctx)

{

	const struct btf_param *param;

	const struct btf_type *t;

	const struct btf_type *type;

	struct btf *btf;

	s32 nr;



	if (!funcname || !nr)

		return ERR_PTR(-EINVAL);

	if (ctx->btf)

		return 0;



	t = btf_find_func_proto(funcname, &btf);

	if (!t)

		return (const struct btf_param *)t;

	if (!ctx->funcname)

		return -EINVAL;



	param = btf_get_func_param(t, nr);

	if (IS_ERR_OR_NULL(param))

		goto err;

	type = btf_find_func_proto(ctx->funcname, &btf);

	if (!type)

		return -ENOENT;



	ctx->btf = btf;

	ctx->proto = type;



	/* ctx->params is optional, since func(void) will not have params. */

	nr = 0;

	param = btf_get_func_param(type, &nr);

	if (!IS_ERR_OR_NULL(param)) {

		/* Hide the first 'data' argument of tracepoint */

	if (tracepoint) {

		(*nr)--;

		if (ctx->flags & TPARG_FL_TPOINT) {

			nr--;

			param++;

		}

	}



	if (*nr > 0) {

		*btf_p = btf;

		return param;

	if (nr > 0) {

		ctx->nr_params = nr;

		ctx->params = param;

	} else {

		ctx->nr_params = 0;

		ctx->params = NULL;

	}



err:

	btf_put(btf);

	return NULL;

	return 0;

}



static void clear_btf_context(struct traceprobe_parse_context *ctx)
@@ -403,6 +411,7 @@ static void clear_btf_context(struct traceprobe_parse_context *ctx) 
	if (ctx->btf) {

		btf_put(ctx->btf);

		ctx->btf = NULL;

		ctx->proto = NULL;

		ctx->params = NULL;

		ctx->nr_params = 0;

	}
@@ -522,7 +531,7 @@ static int parse_btf_arg(char *varname, 
	const struct btf_param *params;

	const struct btf_type *type;

	char *field = NULL;

	int i, is_ptr;

	int i, is_ptr, ret;

	u32 tid;



	if (WARN_ON_ONCE(!ctx->funcname))
@@ -538,16 +547,36 @@ static int parse_btf_arg(char *varname, 
		return -EOPNOTSUPP;

	}



	if (!ctx->params) {

		params = find_btf_func_param(ctx->funcname,

					     &ctx->nr_params, &ctx->btf,

					     ctx->flags & TPARG_FL_TPOINT);

		if (IS_ERR_OR_NULL(params)) {

	if (ctx->flags & TPARG_FL_RETURN) {

		if (strcmp(varname, "$retval") != 0) {

			trace_probe_log_err(ctx->offset, NO_BTFARG);

			return -ENOENT;

		}

		code->op = FETCH_OP_RETVAL;

		/* Check whether the function return type is not void */

		if (query_btf_context(ctx) == 0) {

			if (ctx->proto->type == 0) {

				trace_probe_log_err(ctx->offset, NO_RETVAL);

				return -ENOENT;

			}

			tid = ctx->proto->type;

			goto found;

		}

		if (field) {

			trace_probe_log_err(ctx->offset + field - varname,

					    NO_BTF_ENTRY);

			return -ENOENT;

		}

		return 0;

	}



	if (!ctx->btf) {

		ret = query_btf_context(ctx);

		if (ret < 0 || ctx->nr_params == 0) {

			trace_probe_log_err(ctx->offset, NO_BTF_ENTRY);

			return PTR_ERR(params);

		}

		ctx->params = params;

	} else

	}

	params = ctx->params;



	for (i = 0; i < ctx->nr_params; i++) {
@@ -559,7 +588,6 @@ static int parse_btf_arg(char *varname, 
				code->param = i + 1;

			else

				code->param = i;



			tid = params[i].type;

			goto found;

		}
@@ -584,7 +612,7 @@ static int parse_btf_arg(char *varname, 
	return 0;

}



static const struct fetch_type *parse_btf_arg_type(

static const struct fetch_type *find_fetch_type_from_btf_type(

					struct traceprobe_parse_context *ctx)

{

	struct btf *btf = ctx->btf;
@@ -596,27 +624,6 @@ static const struct fetch_type *parse_btf_arg_type( 
	return find_fetch_type(typestr, ctx->flags);

}



static const struct fetch_type *parse_btf_retval_type(

					struct traceprobe_parse_context *ctx)

{

	const char *typestr = NULL;

	const struct btf_type *type;

	struct btf *btf;



	if (ctx->funcname) {

		/* Do not use ctx->btf, because it must be used with ctx->param */

		type = btf_find_func_proto(ctx->funcname, &btf);

		if (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);

		}

	}



	return find_fetch_type(typestr, ctx->flags);

}



static int parse_btf_bitfield(struct fetch_insn **pcode,

			      struct traceprobe_parse_context *ctx)

{
@@ -639,30 +646,15 @@ static int parse_btf_bitfield(struct fetch_insn **pcode, 
	return 0;

}



static bool is_btf_retval_void(const char *funcname)

{

	const struct btf_type *t;

	struct btf *btf;

	bool ret;



	t = btf_find_func_proto(funcname, &btf);

	if (!t)

		return false;



	ret = (t->type == 0);

	btf_put(btf);

	return ret;

}

#else

static void clear_btf_context(struct traceprobe_parse_context *ctx)

{

	ctx->btf = NULL;

}



static const struct btf_param *find_btf_func_param(const char *funcname, s32 *nr,

						   struct btf **btf_p, bool tracepoint)

static int query_btf_context(struct traceprobe_parse_context *ctx)

{

	return ERR_PTR(-EOPNOTSUPP);

	return -EOPNOTSUPP;

}



static int parse_btf_arg(char *varname,
@@ -680,24 +672,23 @@ static int parse_btf_bitfield(struct fetch_insn **pcode, 
	return -EOPNOTSUPP;

}



#define parse_btf_arg_type(ctx)		\

#define find_fetch_type_from_btf_type(ctx)		\

	find_fetch_type(NULL, ctx->flags)



#define parse_btf_retval_type(ctx)		\

	find_fetch_type(NULL, ctx->flags)



#define is_btf_retval_void(funcname)	(false)



#endif



#define PARAM_MAX_STACK (THREAD_SIZE / sizeof(unsigned long))



static int parse_probe_vars(char *arg, const struct fetch_type *t,

			    struct fetch_insn *code,

/* Parse $vars. @orig_arg points '$', which syncs to @ctx->offset */

static int parse_probe_vars(char *orig_arg, const struct fetch_type *t,

			    struct fetch_insn **pcode,

			    struct fetch_insn *end,

			    struct traceprobe_parse_context *ctx)

{

	unsigned long param;

	struct fetch_insn *code = *pcode;

	int err = TP_ERR_BAD_VAR;

	char *arg = orig_arg + 1;

	unsigned long param;

	int ret = 0;

	int len;
@@ -716,18 +707,17 @@ static int parse_probe_vars(char *arg, const struct fetch_type *t, 
		goto inval;

	}



	if (strcmp(arg, "retval") == 0) {

		if (ctx->flags & TPARG_FL_RETURN) {

			if ((ctx->flags & TPARG_FL_KERNEL) &&

			    is_btf_retval_void(ctx->funcname)) {

				err = TP_ERR_NO_RETVAL;

	if (str_has_prefix(arg, "retval")) {

		if (!(ctx->flags & TPARG_FL_RETURN)) {

			err = TP_ERR_RETVAL_ON_PROBE;

			goto inval;

		}

		if (!(ctx->flags & TPARG_FL_KERNEL) ||

		    !IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS)) {

			code->op = FETCH_OP_RETVAL;

			return 0;

		}

		err = TP_ERR_RETVAL_ON_PROBE;

		goto inval;

		return parse_btf_arg(orig_arg, pcode, end, ctx);

	}



	len = str_has_prefix(arg, "stack");
@@ -829,7 +819,7 @@ parse_probe_arg(char *arg, const struct fetch_type *type, 


	switch (arg[0]) {

	case '$':

		ret = parse_probe_vars(arg + 1, type, code, ctx);

		ret = parse_probe_vars(arg, type, pcode, end, ctx);

		break;



	case '%':	/* named register */
@@ -1126,12 +1116,9 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size, 
		goto fail;



	/* Update storing type if BTF is available */

	if (IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS) && !t) {

		if (ctx->last_type)

			parg->type = parse_btf_arg_type(ctx);

		else if (ctx->flags & TPARG_FL_RETURN)

			parg->type = parse_btf_retval_type(ctx);

	}

	if (IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS) &&

	    !t && ctx->last_type)

		parg->type = find_fetch_type_from_btf_type(ctx);



	ret = -EINVAL;

	/* Store operation */
@@ -1420,7 +1407,6 @@ const char **traceprobe_expand_meta_args(int argc, const char *argv[], 
	const struct btf_param *params = NULL;

	int i, j, n, used, ret, args_idx = -1;

	const char **new_argv = NULL;

	int nr_params;



	ret = argv_has_var_arg(argc, argv, &args_idx, ctx);

	if (ret < 0)
@@ -1431,9 +1417,8 @@ const char **traceprobe_expand_meta_args(int argc, const char *argv[], 
		return NULL;

	}



	params = find_btf_func_param(ctx->funcname, &nr_params, &ctx->btf,

				     ctx->flags & TPARG_FL_TPOINT);

	if (IS_ERR_OR_NULL(params)) {

	ret = query_btf_context(ctx);

	if (ret < 0 || ctx->nr_params == 0) {

		if (args_idx != -1) {

			/* $arg* requires BTF info */

			trace_probe_log_err(0, NOSUP_BTFARG);
@@ -1442,8 +1427,6 @@ const char **traceprobe_expand_meta_args(int argc, const char *argv[], 
		*new_argc = argc;

		return NULL;

	}

	ctx->params = params;

	ctx->nr_params = nr_params;



	if (args_idx >= 0)

		*new_argc = argc + ctx->nr_params - 1;
@@ -1458,7 +1441,7 @@ const char **traceprobe_expand_meta_args(int argc, const char *argv[], 
	for (i = 0, j = 0; i < argc; i++) {

		trace_probe_log_set_index(i + 2);

		if (i == args_idx) {

			for (n = 0; n < nr_params; n++) {

			for (n = 0; n < ctx->nr_params; n++) {

				ret = sprint_nth_btf_arg(n, "", buf + used,

							 bufsize - used, ctx);

				if (ret < 0)

kernel/trace/trace_probe.h

+1 −0
Original line number Diff line number Diff line
@@ -385,6 +385,7 @@ struct traceprobe_parse_context { 
	struct trace_event_call *event;

	/* BTF related parameters */

	const char *funcname;		/* Function name in BTF */

	const struct btf_type  *proto;	/* Prototype of the function */

	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 */