Date:   Mon, 27 Jun 2022 00:13:30 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Jeff Xie <xiehuan09@...il.com>
Cc:     rostedt@...dmis.org, mingo@...hat.com, mhiramat@...nel.org,
        zanussi@...nel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, shuah@...nel.org,
        linux-doc@...r.kernel.org, corbet@....net, chensong_2000@....cn
Subject: Re: [PATCH v13 2/4] trace/objtrace: Get the value of the object

On Sun, 26 Jun 2022 10:56:02 +0800
Jeff Xie <xiehuan09@...il.com> wrote:

> Using objtrace trigger to get the value of the object which from the kernel
> function parameter.
> 
> Syntax:
> 	objtrace:add:obj[,offset][:type][:count][if <filter>]
> 
> Usage:
> 	# echo 'p bio_add_page arg1=$arg1' > ./kprobe_events
> 	# gdb vmlinux
> 	(gdb) p &(((struct bio *)0)->bi_iter.bi_size)
> 	$1 = (unsigned int *) 0x28
> 	# echo 'objtrace:add:arg1,0x28:u32:1 if comm == "cat"' > ./events/kprobes/ \
> 		 p_bio_add_page_0/trigger
> 	# cat /test.txt
> 

Thanks for update! This looks good to me.

Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>

> Signed-off-by: Jeff Xie <xiehuan09@...il.com>
> ---
>  kernel/trace/trace.c         |   2 +-
>  kernel/trace/trace_entries.h |   5 +-
>  kernel/trace/trace_object.c  | 187 ++++++++++++++++++++++++++++++++---
>  kernel/trace/trace_output.c  |   6 +-
>  4 files changed, 181 insertions(+), 19 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 7074ad8bc1a0..37f5cbfa5347 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -5628,7 +5628,7 @@ static const char readme_msg[] =
>  	"\t            disable_hist:<system>:<event>\n"
>  #endif
>  #ifdef CONFIG_TRACE_OBJECT
> -	"\t            objtrace:add:obj[:count][if <filter>]\n"
> +	"\t            objtrace:add:obj[,offset][:type][:count][if <filter>]\n"
>  #endif
>  #ifdef CONFIG_STACKTRACE
>  	"\t\t    stacktrace\n"
> diff --git a/kernel/trace/trace_entries.h b/kernel/trace/trace_entries.h
> index bb120d9498a9..2407c45a568c 100644
> --- a/kernel/trace/trace_entries.h
> +++ b/kernel/trace/trace_entries.h
> @@ -413,8 +413,9 @@ FTRACE_ENTRY(object, trace_object_entry,
>  		__field(	unsigned long,		ip		)
>  		__field(	unsigned long,		parent_ip	)
>  		__field(	unsigned long,		object		)
> +		__field(	unsigned long,		value		)
>  	),
>  
> -	F_printk(" %ps <-- %ps object:%lx\n",
> -		 (void *)__entry->ip, (void *)__entry->parent_ip, __entry->object)
> +	F_printk(" %ps <-- %ps object:%lx value:%lx\n", (void *)__entry->ip,
> +	       (void *)__entry->parent_ip, __entry->object, __entry->value)
>  );
> diff --git a/kernel/trace/trace_object.c b/kernel/trace/trace_object.c
> index 19ec4b1c0186..611341abeb7c 100644
> --- a/kernel/trace/trace_object.c
> +++ b/kernel/trace/trace_object.c
> @@ -16,8 +16,14 @@ static const int max_args_num = 6;
>  static void exit_trace_object(struct trace_array *tr);
>  static int init_trace_object(struct trace_array *tr);
>  
> +/*
> + * get the offset from the special object and
> + * the type size of the value
> + */
>  struct object_instance {
>  	void *obj;
> +	int obj_offset;
> +	int obj_value_type_size;
>  	struct trace_array *tr;
>  };
>  
> @@ -25,9 +31,23 @@ struct object_instance {
>  struct objtrace_trigger_data {
>  	struct ftrace_event_field *field;
>  	char objtrace_cmd[OBJTRACE_CMD_LEN];
> +	int obj_offset;
> +	int obj_value_type_size;
>  	struct trace_array *tr;
>  };
>  
> +/* get the type size for the special object */
> +struct objtrace_fetch_type {
> +	char *name;
> +	int type_size;
> +};
> +
> +enum objattr {
> +	OBJ_OFFSET,
> +	OBJ_VAL_TYPE_SIZE,
> +	MAX_OBJ_ATTR
> +};
> +
>  /* objtrace data with fops and objtrace_instances */
>  struct objtrace_data {
>  	struct list_head head;
> @@ -67,6 +87,35 @@ static bool object_exist(void *obj, struct trace_array *tr)
>  	return false;
>  }
>  
> +static int get_object_attr(void *obj, int objattr,
> +		struct trace_array *tr, int *result)
> +{
> +	int i, max;
> +	struct objtrace_data *obj_data;
> +
> +	obj_data = get_obj_data(tr);
> +	if (!obj_data)
> +		return -EINVAL;
> +
> +	max = READ_ONCE(obj_data->num_traced_obj);
> +	smp_rmb();
> +	for (i = 0; i < max; i++) {
> +		if (obj_data->traced_obj[i].obj == obj) {
> +			switch (objattr) {
> +			case OBJ_OFFSET:
> +				*result = obj_data->traced_obj[i].obj_offset;
> +				return 0;
> +			case OBJ_VAL_TYPE_SIZE:
> +				*result = obj_data->traced_obj[i].obj_value_type_size;
> +				return 0;
> +			default:
> +				return -EINVAL;
> +			}
> +		}
> +	}
> +	return -EINVAL;
> +}
> +
>  static bool object_empty(struct trace_array *tr)
>  {
>  	struct objtrace_data *obj_data;
> @@ -78,7 +127,8 @@ static bool object_empty(struct trace_array *tr)
>  	return !READ_ONCE(obj_data->num_traced_obj);
>  }
>  
> -static void set_trace_object(void *obj, struct trace_array *tr)
> +static void set_trace_object(void *obj, int obj_offset,
> +			int obj_value_type_size, struct trace_array *tr)
>  {
>  	unsigned long flags;
>  	struct object_instance *obj_ins;
> @@ -103,6 +153,8 @@ static void set_trace_object(void *obj, struct trace_array *tr)
>  	}
>  	obj_ins = &obj_data->traced_obj[READ_ONCE(obj_data->num_traced_obj)];
>  	obj_ins->obj = obj;
> +	obj_ins->obj_value_type_size = obj_value_type_size;
> +	obj_ins->obj_offset = obj_offset;
>  	obj_ins->tr = tr;
>  	/* make sure the num_traced_obj update always appears after traced_obj update */
>  	smp_wmb();
> @@ -112,7 +164,7 @@ static void set_trace_object(void *obj, struct trace_array *tr)
>  }
>  
>  static void submit_trace_object(unsigned long ip, unsigned long parent_ip,
> -				 unsigned long object, struct trace_array *tr)
> +		unsigned long object, unsigned long value, struct trace_array *tr)
>  {
>  
>  	struct trace_buffer *buffer = tr->array_buffer.buffer;
> @@ -129,10 +181,43 @@ static void submit_trace_object(unsigned long ip, unsigned long parent_ip,
>  	entry->ip                       = ip;
>  	entry->parent_ip                = parent_ip;
>  	entry->object			= object;
> +	entry->value			= value;
>  
>  	trace_buffer_unlock_commit(tr, buffer, event, trace_ctx);
>  }
>  
> +static inline long get_object_value(unsigned long *val, void *obj, int type_size)
> +{
> +	char tmp[sizeof(u64)];
> +	long ret = 0;
> +
> +	ret = copy_from_kernel_nofault(tmp, obj, sizeof(tmp));
> +	if (ret)
> +		return ret;
> +	switch (type_size) {
> +	case 1: {
> +		*val = (unsigned long)*(u8 *)tmp;
> +		break;
> +	}
> +	case 2: {
> +		*val = (unsigned long)*(u16 *)tmp;
> +		break;
> +	}
> +	case 4: {
> +		*val = (unsigned long)*(u32 *)tmp;
> +		break;
> +	}
> +	case 8: {
> +		*val = (unsigned long)*(u64 *)tmp;
> +		break;
> +	}
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
>  static void
>  trace_object_events_call(unsigned long ip, unsigned long parent_ip,
>  		struct ftrace_ops *op, struct ftrace_regs *fregs)
> @@ -140,7 +225,8 @@ trace_object_events_call(unsigned long ip, unsigned long parent_ip,
>  	struct pt_regs *pt_regs = ftrace_get_regs(fregs);
>  	struct trace_array *tr = op->private;
>  	struct trace_array_cpu *data;
> -	unsigned long obj;
> +	int ret, val_type_size, obj_offset;
> +	unsigned long obj, val;
>  	long disabled;
>  	int cpu, n;
>  
> @@ -154,8 +240,21 @@ trace_object_events_call(unsigned long ip, unsigned long parent_ip,
>  			goto out;
>  		for (n = 0; n < max_args_num; n++) {
>  			obj = regs_get_kernel_argument(pt_regs, n);
> -			if (object_exist((void *)obj, tr))
> -				submit_trace_object(ip, parent_ip, obj, tr);
> +			if (object_exist((void *)obj, tr)) {
> +				ret = get_object_attr((void *)obj, OBJ_OFFSET,
> +						tr, &obj_offset);
> +				if (unlikely(ret) < 0)
> +					goto out;
> +				ret = get_object_attr((void *)obj, OBJ_VAL_TYPE_SIZE,
> +						tr, &val_type_size);
> +				if (unlikely(ret) < 0)
> +					goto out;
> +				if (get_object_value(&val, (void *)(obj + obj_offset),
> +							val_type_size))
> +					continue;
> +
> +				submit_trace_object(ip, parent_ip, obj, val, tr);
> +			}
>  		/* The parameters of a function may match multiple objects */
>  		}
>  	}
> @@ -176,9 +275,23 @@ trace_object_trigger(struct event_trigger_data *data,
>  
>  	field = obj_data->field;
>  	memcpy(&obj, rec + field->offset, sizeof(obj));
> -	set_trace_object(obj, tr);
> +	/* set the offset from the special object and the type size of the value*/
> +	set_trace_object(obj, obj_data->obj_offset,
> +			obj_data->obj_value_type_size, tr);
>  }
>  
> +static const struct objtrace_fetch_type objtrace_fetch_types[] = {
> +	{"u8", 1},
> +	{"x8", 1},
> +	{"u16", 2},
> +	{"x16", 2},
> +	{"u32", 4},
> +	{"x32", 4},
> +	{"u64", 8},
> +	{"x64", 8},
> +	{NULL, 0},
> +};
> +
>  static void
>  trace_object_trigger_free(struct event_trigger_data *data)
>  {
> @@ -213,14 +326,25 @@ static int
>  event_trigger_print(const char *name, struct seq_file *m,
>  		void *data, char *filter_str, void *objtrace_data)
>  {
> +	int i;
>  	long count = (long)data;
>  	struct objtrace_trigger_data *obj_data = objtrace_data;
> +	const char *value_type_name;
>  
>  	seq_puts(m, name);
>  
>  	seq_printf(m, ":%s", obj_data->objtrace_cmd);
>  	seq_printf(m, ":%s", obj_data->field->name);
> +	if (obj_data->obj_offset)
> +		seq_printf(m, ",0x%x", obj_data->obj_offset);
>  
> +	for (i = 0; objtrace_fetch_types[i].name; i++) {
> +		if (objtrace_fetch_types[i].type_size == obj_data->obj_value_type_size) {
> +			value_type_name = objtrace_fetch_types[i].name;
> +			break;
> +		}
> +	}
> +	seq_printf(m, ":%s", value_type_name);
>  	if (count == -1)
>  		seq_puts(m, ":unlimited");
>  	else
> @@ -303,16 +427,18 @@ event_object_trigger_parse(struct event_command *cmd_ops,
>  	struct event_trigger_data *trigger_data;
>  	struct objtrace_trigger_data *obj_data;
>  	struct ftrace_event_field *field;
> -	char *objtrace_cmd, *arg;
> -	char *param, *filter;
> -	int ret;
> +	char *objtrace_cmd, *obj;
> +	char *param, *filter, *str, *type;
> +	int ret, i, def_type_size, obj_value_type_size = 0;
> +	char *tmp_saved_param;
> +	long offset = 0;
>  	bool remove;
>  
>  	remove = event_trigger_check_remove(glob);
>  
>  	/*
>  	 * separate the param and the filter:
> -	 * objtrace:add:OBJ[:COUNT] [if filter]
> +	 * objtrace:add:OBJ[,OFFS][:TYPE][:COUNT] [if filter]
>  	 */
>  	ret = event_trigger_separate_filter(param_and_filter, &param, &filter, true);
>  	if (ret)
> @@ -324,11 +450,44 @@ event_object_trigger_parse(struct event_command *cmd_ops,
>  		return -EINVAL;
>  	}
>  
> -	arg = strsep(&param, ":");
> -	if (!arg)
> +	obj = strsep(&param, ":");
> +	if (!obj)
>  		return -EINVAL;
>  
> -	field = trace_find_event_field(file->event_call, arg);
> +	str = strchr(obj, ',');
> +	if (!str)
> +		offset = 0;
> +	else {
> +		*str++ = '\0';
> +		ret = kstrtol(str, 0, &offset);
> +		if (ret)
> +			return -EINVAL;
> +	}
> +	def_type_size = sizeof(void *);
> +	if (!param) {
> +		obj_value_type_size = def_type_size;
> +		goto skip_get_type;
> +	}
> +	tmp_saved_param = param;
> +	type = strsep(&param, ":");
> +	if (!type)
> +		obj_value_type_size = def_type_size;
> +	/* if this is the trigger count */
> +	else if (isdigit(type[0])) {
> +		obj_value_type_size = def_type_size;
> +		param = tmp_saved_param;
> +	} else {
> +		for (i = 0; objtrace_fetch_types[i].name; i++) {
> +			if (strcmp(objtrace_fetch_types[i].name, type) == 0) {
> +				obj_value_type_size = objtrace_fetch_types[i].type_size;
> +				break;
> +			}
> +		}
> +	}
> +	if (!obj_value_type_size)
> +		return -EINVAL;
> +skip_get_type:
> +	field = trace_find_event_field(file->event_call, obj);
>  	if (!field)
>  		return -EINVAL;
>  
> @@ -345,6 +504,8 @@ event_object_trigger_parse(struct event_command *cmd_ops,
>  		return -ENOMEM;
>  
>  	obj_data->field = field;
> +	obj_data->obj_offset = offset;
> +	obj_data->obj_value_type_size = obj_value_type_size;
>  	obj_data->tr = file->tr;
>  	snprintf(obj_data->objtrace_cmd, OBJTRACE_CMD_LEN, objtrace_cmd);
>  
> diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
> index 34ff7b4dc521..a45871b52dcc 100644
> --- a/kernel/trace/trace_output.c
> +++ b/kernel/trace/trace_output.c
> @@ -1561,6 +1561,7 @@ static enum print_line_t trace_object_print(struct trace_iterator *iter, int fla
>  	trace_assign_type(field, iter->ent);
>  	print_fn_trace(s, field->ip, field->parent_ip, flags);
>  	trace_seq_printf(s, " object:0x%lx", field->object);
> +	trace_seq_printf(s, " value:0x%lx", field->value);
>  	trace_seq_putc(s, '\n');
>  
>  	return trace_handle_return(s);
> @@ -1573,9 +1574,8 @@ static enum print_line_t trace_object_raw(struct trace_iterator *iter, int flags
>  
>  	trace_assign_type(field, iter->ent);
>  
> -	trace_seq_printf(&iter->seq, "%lx %lx\n",
> -			 field->ip,
> -			 field->parent_ip);
> +	trace_seq_printf(&iter->seq, "%lx %lx %lx %lx\n", field->ip,
> +			field->parent_ip, field->object, field->value);
>  
>  	return trace_handle_return(&iter->seq);
>  }
> -- 
> 2.25.1
> 


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

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