Re: [PATCH 4/4] uprobes/tracing: generalize structuprobe_trace_entry_head

[Steven Rostedt]

On Fri, 2013-03-29 at 19:15 +0100, Oleg Nesterov wrote:
> struct uprobe_trace_entry_head has a single member for reporting,
> "unsigned long ip". If we want to support uretprobes we need to
> create another struct which has "func" and "ret_ip" and duplicate
> a lot of functions, like trace_kprobe.c does.
> 
> To avoid this copy-and-paste horror we turn ->ip into ->vaddr[]
> and add couple of trivial helpers to calculate sizeof/data. This
> uglifies the code a bit, but this allows us to avoid a lot more
> complications later, when we add the support for ret-probes.
> 
> Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
> ---
>  kernel/trace/trace.h        |    5 ---
>  kernel/trace/trace_uprobe.c |   61 ++++++++++++++++++++++++------------------
>  2 files changed, 35 insertions(+), 31 deletions(-)
> 
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 57d7e53..6ca57cf 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -103,11 +103,6 @@ struct kretprobe_trace_entry_head {
>  	unsigned long		ret_ip;
>  };
>  
> -struct uprobe_trace_entry_head {
> -	struct trace_entry	ent;
> -	unsigned long		ip;
> -};
> -
>  /*
>   * trace_flag_type is an enumeration that holds different
>   * states when a trace occurs. These are:
> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> index 43d258d..92a4b08 100644
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -28,6 +28,17 @@
>  
>  #define UPROBE_EVENT_SYSTEM	"uprobes"
>  
> +struct uprobe_trace_entry_head {
> +	struct trace_entry	ent;
> +	unsigned long		vaddr[];
> +};
> +
> +#define SIZEOF_TRACE_ENTRY(nr)	\
> +	(sizeof(struct uprobe_trace_entry_head) + sizeof(unsigned long) * (nr))
> +
> +#define DATAOF_TRACE_ENTRY(entry, nr)	\
> +	((void*)&(entry)->vaddr[nr])
> +
>  struct trace_uprobe_filter {
>  	rwlock_t		rwlock;
>  	int			nr_systemwide;
> @@ -491,20 +502,19 @@ static int uprobe_trace_func(struct trace_uprobe *tu, struct pt_regs *regs)
>  	struct uprobe_trace_entry_head *entry;
>  	struct ring_buffer_event *event;
>  	struct ring_buffer *buffer;
> -	u8 *data;
> +	void *data;
>  	int size, i;
>  	struct ftrace_event_call *call = &tu->call;
>  
> -	size = sizeof(*entry) + tu->size;
> -
> +	size = SIZEOF_TRACE_ENTRY(1) + tu->size;

That '1' is confusing. When I first looked at this code, I thought it
was a bug as it should have been '0' (thinking of arrays). And then I
realized that you want the entry *after* the element.

Instead of '1' and I assume '2' for ret probes, how about defining an
enum:

enum {
	UPROBE_NORM	= 1,
	UPROBE_RET	= 2,
};

and then you can have;

	size = SIZEOF_TRACE_ENTRY(UPROBE_NORM);

and later:

	size = SIZEOF_TRACE_ENTRY(UPROBE_RET);

Same goes for DATAOF_TRACE_ENTRY().

This would make it a lot easier to understand and review, and much less
bug prone when we have to deal with two different types of
uprobe_trace_entry_head's.

-- Steve

>  	event = trace_current_buffer_lock_reserve(&buffer, call->event.type,
>  						  size, 0, 0);
>  	if (!event)
>  		return 0;
>  
>  	entry = ring_buffer_event_data(event);
> -	entry->ip = instruction_pointer(regs);
> -	data = (u8 *)&entry[1];
> +	entry->vaddr[0] = instruction_pointer(regs);
> +	data = DATAOF_TRACE_ENTRY(entry, 1);
>  	for (i = 0; i < tu->nr_args; i++)
>  		call_fetch(&tu->args[i].fetch, regs, data + tu->args[i].offset);
>  
> @@ -518,22 +528,22 @@ static int uprobe_trace_func(struct trace_uprobe *tu, struct pt_regs *regs)
>  static enum print_line_t
>  print_uprobe_event(struct trace_iterator *iter, int flags, struct trace_event *event)
>  {
> -	struct uprobe_trace_entry_head *field;
> +	struct uprobe_trace_entry_head *entry;
>  	struct trace_seq *s = &iter->seq;
>  	struct trace_uprobe *tu;
>  	u8 *data;
>  	int i;
>  
> -	field = (struct uprobe_trace_entry_head *)iter->ent;
> +	entry = (struct uprobe_trace_entry_head *)iter->ent;
>  	tu = container_of(event, struct trace_uprobe, call.event);
>  
> -	if (!trace_seq_printf(s, "%s: (0x%lx)", tu->call.name, field->ip))
> +	if (!trace_seq_printf(s, "%s: (0x%lx)", tu->call.name, entry->vaddr[0]))
>  		goto partial;
>  
> -	data = (u8 *)&field[1];
> +	data = DATAOF_TRACE_ENTRY(entry, 1);
>  	for (i = 0; i < tu->nr_args; i++) {
>  		if (!tu->args[i].type->print(s, tu->args[i].name,
> -					     data + tu->args[i].offset, field))
> +					     data + tu->args[i].offset, entry))
>  			goto partial;
>  	}
>  
> @@ -585,16 +595,17 @@ static void probe_event_disable(struct trace_uprobe *tu, int flag)
>  
>  static int uprobe_event_define_fields(struct ftrace_event_call *event_call)
>  {
> -	int ret, i;
> +	int ret, i, size;
>  	struct uprobe_trace_entry_head field;
> -	struct trace_uprobe *tu = (struct trace_uprobe *)event_call->data;
> +	struct trace_uprobe *tu = event_call->data;
>  
> -	DEFINE_FIELD(unsigned long, ip, FIELD_STRING_IP, 0);
> +	DEFINE_FIELD(unsigned long, vaddr[0], FIELD_STRING_IP, 0);
> +	size = SIZEOF_TRACE_ENTRY(1);
>  	/* Set argument names as fields */
>  	for (i = 0; i < tu->nr_args; i++) {
>  		ret = trace_define_field(event_call, tu->args[i].type->fmttype,
>  					 tu->args[i].name,
> -					 sizeof(field) + tu->args[i].offset,
> +					 size + tu->args[i].offset,
>  					 tu->args[i].type->size,
>  					 tu->args[i].type->is_signed,
>  					 FILTER_OTHER);
> @@ -748,33 +759,31 @@ static int uprobe_perf_func(struct trace_uprobe *tu, struct pt_regs *regs)
>  	struct ftrace_event_call *call = &tu->call;
>  	struct uprobe_trace_entry_head *entry;
>  	struct hlist_head *head;
> -	u8 *data;
> -	int size, __size, i;
> -	int rctx;
> +	unsigned long ip;
> +	void *data;
> +	int size, rctx, i;
>  
>  	if (!uprobe_perf_filter(&tu->consumer, 0, current->mm))
>  		return UPROBE_HANDLER_REMOVE;
>  
> -	__size = sizeof(*entry) + tu->size;
> -	size = ALIGN(__size + sizeof(u32), sizeof(u64));
> -	size -= sizeof(u32);
> +	size = SIZEOF_TRACE_ENTRY(1);
> +	size = ALIGN(size + tu->size + sizeof(u32), sizeof(u64)) - sizeof(u32);
>  	if (WARN_ONCE(size > PERF_MAX_TRACE_SIZE, "profile buffer not large enough"))
>  		return 0;
>  
>  	preempt_disable();
> -
>  	entry = perf_trace_buf_prepare(size, call->event.type, regs, &rctx);
>  	if (!entry)
>  		goto out;
>  
> -	entry->ip = instruction_pointer(regs);
> -	data = (u8 *)&entry[1];
> +	ip = instruction_pointer(regs);
> +	entry->vaddr[0] = ip;
> +	data = DATAOF_TRACE_ENTRY(entry, 1);
>  	for (i = 0; i < tu->nr_args; i++)
>  		call_fetch(&tu->args[i].fetch, regs, data + tu->args[i].offset);
>  
>  	head = this_cpu_ptr(call->perf_events);
> -	perf_trace_buf_submit(entry, size, rctx, entry->ip, 1, regs, head, NULL);
> -
> +	perf_trace_buf_submit(entry, size, rctx, ip, 1, regs, head, NULL);
>   out:
>  	preempt_enable();
>  	return 0;
> @@ -784,7 +793,7 @@ static int uprobe_perf_func(struct trace_uprobe *tu, struct pt_regs *regs)
>  static
>  int trace_uprobe_register(struct ftrace_event_call *event, enum trace_reg type, void *data)
>  {
> -	struct trace_uprobe *tu = (struct trace_uprobe *)event->data;
> +	struct trace_uprobe *tu = event->data;
>  
>  	switch (type) {
>  	case TRACE_REG_REGISTER:


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