Re: [PATCH v2 1/3] tracing/syscalls: Rename variable 'nr' to 'syscall_nr'

[Taeung Song <treeze.taeung@gmail.com>]

On 02/26/2016 10:46 PM, Arnaldo Carvalho de Melo wrote:
> Em Fri, Feb 26, 2016 at 09:24:46PM +0900, Taeung Song escreveu:
>> Hi, Arnaldo
>>
>> On 02/26/2016 03:42 AM, Arnaldo Carvalho de Melo wrote:
>>> Em Fri, Feb 26, 2016 at 03:31:19AM +0900, Taeung Song escreveu:
>>>> Hi, Arnaldo
>>>>
>>>> On 02/26/2016 02:57 AM, Arnaldo Carvalho de Melo wrote:
>>>>> Em Fri, Feb 26, 2016 at 02:38:57AM +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:
>>>>>>              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
>>>>>
>>>>> Please test this with 'perf trace', which this patch breaks, this patch
>>>>> should make it understand this 3rd variation of the non common list of
>>>>> fields in syscall tracepoints:
>>>>
>>>> OK, I will test it.
>>>> But IMHO, I think the bottom change has a problem.
>>>> Because sys_enter_io_getevent() has a argument 'long nr'.
>>>
>>> It doesn't matter
>>>
>>>> So this if statement must not have strcmp(sc->args->name, "nr") == 0.
>>>
>>> This is checking for the first variable, if that has that name, it
>>> should be discarded, as in the past it wasn't there, so for the tool to
>>> work on kernels with "nr" as the first (for the syscall number) variable
>>> and for kernels without it, we must check and discard.
>>>
>>> Now we must check and discard the first "nr" (for kernels with this
>>> meaning the syscall number) and also if it is called "syscall_nr").
>>> The other fields are taken as the syscall arguments, in the order that
>>> they come, that is what what we will match with what is in the
>>> raw_syscalls:sys_enter args array:
>>>
>>> [root@jouet ~]# cat
>>> /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/format
>>> name: sys_enter
>>> ID: 17
>>> 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:long id;	offset:8;	size:8;	signed:1;
>>> 	field:unsigned long args[6];	offset:16;	size:48; signed:0;
>>>
>>> print fmt: "NR %ld (%lx, %lx, %lx, %lx, %lx, %lx)", REC->id,
>>> REC->args[0], REC->args[1], REC->args[2], REC->args[3], REC->args[4],
>>> REC->args[5]
>>> [root@jouet ~]#
>>>
>>>> + if (sc->args && strcmp(sc->args->name, "syscall_nr") == 0) {
>>>>
>>>> I think the above instance seem better than the bottom.
>>>>
>>>> +	if (sc->args && (strcmp(sc->args->name, "syscall_nr") ||
>>>> strcmp(sc->args->name, "nr")) == 0) {
>>>
>>> Right in this 'if' body we do:
>>>
>>> 		sc->args = sc->args->next;
>>> 		sc->nr_args--;
>>>
>>> something like that.
>>>
>>> - Arnaldo
>>>
>>>> But I'll test again with perf-trace.
>>>
>>> Right, look at the output of 'perf trace' before and after, so that you
>>> can check if, say, we're using that syscall_nr value as the fd for the
>>> 'write' syscall ('fd' comes right after 'nr'/'syscall_nr').
>>>
>>
>> Sorry, I'm late.
>>
>> I tested perf-trace with the bottom change.
>> (does not rename it to '__syscall_nr' on kernel)
>
> "With this change:"
>
>>
>> +        if (sc->args && (strcmp(sc->args->name, "__syscall_nr") ||
>> strcmp(sc->args->name, "nr")) == 0) {
>>                   sc->args = sc->args->next;
>>                   --sc->nr_args;
>>           }
>>
>> But there are some problems as below.
>
> Right, there is a silly error, we have to test both strcmp(), checking
> if one of them is equal to zero, i.e. if there was a match.
>

I got it. so I sent this change as new patch
"[PATCH 2/2] perf trace: Check and discard not only 'nr' but also 
'__syscall_nr'"
to you as below :-)

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index 20916dd..a252f3a 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -1724,8 +1724,12 @@ static int trace__read_syscall_info(struct trace 
*trace, int id)

          sc->args = sc->tp_format->format.fields;
          sc->nr_args = sc->tp_format->format.nr_fields;
-        /* drop nr field - not relevant here; does not exist on older 
kernels */
-        if (sc->args && strcmp(sc->args->name, "nr") == 0) {
+        /*
+         * We need to check and discard the first variable '__syscall_nr'
+         * or 'nr' that mean the syscall number. It is needless here.
+         * So drop '__syscall_nr' or 'nr' field but does not exist on 
older kernels.
+         */
+        if (sc->args && (!strcmp(sc->args->name, "__syscall_nr") || 
!strcmp(sc->args->name, "nr"))) {
                  sc->args = sc->args->next;
                  --sc->nr_args;
          }


Thanks,
Taeung