[RFC] Re: [PATCH v3 1/2] tracing/syscalls: Rename variable 'nr' to '__syscall_nr'

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Fri, Feb 26, 2016 at 10:14:06PM +0900, Taeung Song escreveu:
> There is a problem about duplicated variable name i.e.
> 
>     # cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_io_getevents/format
>     name: sys_enter_io_getevents
>     ID: 739
>     format:

Steven, what do you think?

Should we break this ABI while disambiguating the 'nr' field, using
'__syscall_nr' in an attempt to use a name that is unlikely to be used
by a real syscall argument name?

If we stand by published ABIs, we should keep it written in stone and
state that the first 'nr' means '__syscall_nr' while keeping it as-is,
the change for 'perf trace' in that case is to do nothing, it work
as-is, we have just to fix the python binding to do that rename.

Perhaps we can live with that, to avoid having three different cases:
!nr, nr and __syscall_nr.

Ingo, Peter, have you guys followed this case?

Summary: Some tracepoint have multiple fields with the same name, 'nr',
         the first one is a unique syscall ID, the other is a syscall
         argument:

[root@jouet ~]# cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_io_getevents/format 
name: sys_enter_io_getevents
ID: 747
format:
	field:unsigned short common_type;	offset:0;	size:2;	signed:0;
	field:unsigned char common_flags;	offset:2;	size:1;	signed:0;
	field:unsigned char common_preempt_count;	offset:3;	size:1;	signed:0;
	field:int common_pid;	offset:4;	size:4;	signed:1;

	field:int nr;	offset:8;	size:4;	signed:1;
	field:aio_context_t ctx_id;	offset:16;	size:8;	signed:0;
	field:long min_nr;	offset:24;	size:8;	signed:0;
	field:long nr;	offset:32;	size:8;	signed:0;
	field:struct io_event * events;	offset:40;	size:8;	signed:0;
	field:struct timespec * timeout;	offset:48;	size:8;	signed:0;

print fmt: "ctx_id: 0x%08lx, min_nr: 0x%08lx, nr: 0x%08lx, events: 0x%08lx, timeout: 0x%08lx", ((unsigned long)(REC->ctx_id)), ((unsigned long)(REC->min_nr)), ((unsigned long)(REC->nr)), ((unsigned long)(REC->events)), ((unsigned long)(REC->timeout))
[root@jouet ~]#

- Arnaldo

>             field:unsigned short common_type; offset:0;  size:2; signed:0;
>             field:unsigned char common_flags; offset:2;  size:1; signed:0;
>             field:unsigned char common_preempt_count; offset:3; size:1; signed:0;
>             field:int common_pid;offset:4;size:4;signed:1;
>             field:int nr;                     offset:8;  size:4; signed:1;
>             field:aio_context_t ctx_id;       offset:16; size:8; signed:0;
>             field:long min_nr;                offset:24; size:8; signed:0;
>             field:long nr;                    offset:32; size:8; signed:0;
>             field:struct io_event * events;   offset:40; size:8; signed:0;
>             field:struct timespec * timeout;  offset:48; size:8; signed:0;
> 
>             print fmt: "ctx_id: 0x%08lx, min_nr: 0x%08lx, nr: 0x%08lx,
>                         events: 0x%08lx, timeout: 0x%08lx", ((unsigned long)(REC->ctx_id)),
>                         ((unsigned long)(REC->min_nr)), ((unsigned long)(REC->nr)),
>                         ((unsigned long)(REC->events)), ((unsigned long)(REC->timeout))
> 
> As above 'int nr;' and 'long nr;' variables have
> duplicated name so problems are occurred in perf-script i.e.
> 
>     # perf record -e syscalls:*
>     # perf script -g python
>     # perf script -s perf-script.py
>       File "perf-script.py", line 8694
>         def syscalls__sys_enter_io_getevents(event_name, context, common_cpu,
>     SyntaxError: duplicate argument 'nr' in function definition
>     Error running python script perf-script.py
> 
> As above, problems about duplicated argument occurred.
> Not only sys_enter_io_getevent() but also sys_enter_io_submit()
> have relevevance to this problem.
> 
> So rename a variable 'nr' to '__syscall_nr' for system call number
> in print_syscall_enter() and etc.
> 
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Lai Jiangshan <jiangshanlai@gmail.com>
> Signed-off-by: Taeung Song <treeze.taeung@gmail.com>
> ---
>  kernel/trace/trace.h          |  4 ++--
>  kernel/trace/trace_syscalls.c | 16 ++++++++--------
>  2 files changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 8414fa4..98b3c66 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -88,13 +88,13 @@ enum trace_type {
>   */
>  struct syscall_trace_enter {
>  	struct trace_entry	ent;
> -	int			nr;
> +	int			__syscall_nr;
>  	unsigned long		args[];
>  };
>  
>  struct syscall_trace_exit {
>  	struct trace_entry	ent;
> -	int			nr;
> +	int			__syscall_nr;
>  	long			ret;
>  };
>  
> diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
> index 0655afb..90bb468 100644
> --- a/kernel/trace/trace_syscalls.c
> +++ b/kernel/trace/trace_syscalls.c
> @@ -118,7 +118,7 @@ print_syscall_enter(struct trace_iterator *iter, int flags,
>  	int i, syscall;
>  
>  	trace = (typeof(trace))ent;
> -	syscall = trace->nr;
> +	syscall = trace->__syscall_nr;
>  	entry = syscall_nr_to_meta(syscall);
>  
>  	if (!entry)
> @@ -164,7 +164,7 @@ print_syscall_exit(struct trace_iterator *iter, int flags,
>  	struct syscall_metadata *entry;
>  
>  	trace = (typeof(trace))ent;
> -	syscall = trace->nr;
> +	syscall = trace->__syscall_nr;
>  	entry = syscall_nr_to_meta(syscall);
>  
>  	if (!entry) {
> @@ -261,7 +261,7 @@ static int __init syscall_enter_define_fields(struct trace_event_call *call)
>  	int i;
>  	int offset = offsetof(typeof(trace), args);
>  
> -	ret = trace_define_field(call, SYSCALL_FIELD(int, nr), FILTER_OTHER);
> +	ret = trace_define_field(call, SYSCALL_FIELD(int, __syscall_nr), FILTER_OTHER);
>  	if (ret)
>  		return ret;
>  
> @@ -281,7 +281,7 @@ static int __init syscall_exit_define_fields(struct trace_event_call *call)
>  	struct syscall_trace_exit trace;
>  	int ret;
>  
> -	ret = trace_define_field(call, SYSCALL_FIELD(int, nr), FILTER_OTHER);
> +	ret = trace_define_field(call, SYSCALL_FIELD(int, __syscall_nr), FILTER_OTHER);
>  	if (ret)
>  		return ret;
>  
> @@ -332,7 +332,7 @@ static void ftrace_syscall_enter(void *data, struct pt_regs *regs, long id)
>  		return;
>  
>  	entry = ring_buffer_event_data(event);
> -	entry->nr = syscall_nr;
> +	entry->__syscall_nr = syscall_nr;
>  	syscall_get_arguments(current, regs, 0, sys_data->nb_args, entry->args);
>  
>  	event_trigger_unlock_commit(trace_file, buffer, event, entry,
> @@ -378,7 +378,7 @@ static void ftrace_syscall_exit(void *data, struct pt_regs *regs, long ret)
>  		return;
>  
>  	entry = ring_buffer_event_data(event);
> -	entry->nr = syscall_nr;
> +	entry->__syscall_nr = syscall_nr;
>  	entry->ret = syscall_get_return_value(current, regs);
>  
>  	event_trigger_unlock_commit(trace_file, buffer, event, entry,
> @@ -579,7 +579,7 @@ static void perf_syscall_enter(void *ignore, struct pt_regs *regs, long id)
>  	if (!rec)
>  		return;
>  
> -	rec->nr = syscall_nr;
> +	rec->__syscall_nr = syscall_nr;
>  	syscall_get_arguments(current, regs, 0, sys_data->nb_args,
>  			       (unsigned long *)&rec->args);
>  	perf_trace_buf_submit(rec, size, rctx, 0, 1, regs, head, NULL);
> @@ -652,7 +652,7 @@ static void perf_syscall_exit(void *ignore, struct pt_regs *regs, long ret)
>  	if (!rec)
>  		return;
>  
> -	rec->nr = syscall_nr;
> +	rec->__syscall_nr = syscall_nr;
>  	rec->ret = syscall_get_return_value(current, regs);
>  	perf_trace_buf_submit(rec, size, rctx, 0, 1, regs, head, NULL);
>  }
> -- 
> 2.5.0