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

[Taeung Song]

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)

+        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.

0.322 ( 0.012 ms): a.out/27045 write(nr: 3, fd: 4196046, buf: 0x4, 
count: 2140 ) = 4

So, I modified the above change. (I'll send it as new patch)
And then I tested again as below

0.345 ( 0.016 ms): a.out/27695 write(fd: 3, buf: 0x4006ce, count: 4 ) = 4

And I tested perf-trace with renamed '__syscall_nr' on modified kernel.
Everything is ok for aught I know.

0.345 ( 0.016 ms): a.out/27695 write(fd: 3, buf: 0x4006ce, count: 4 ) = 4

I'm writing another patchset. I'll send it soon.

Thanks,
Taeung