Re: [PATCH v2 2/3] tracing: expose current->comm to [ku]probe events

[Namhyung Kim <namhyung@kernel.org>]

Hello,

On Tue, Jun 07, 2016 at 04:24:23PM +0900, Masami Hiramatsu wrote:
> On Thu,  2 Jun 2016 18:11:02 -0700
> Omar Sandoval <osandov@osandov.com> wrote:
> 
> > From: Omar Sandoval <osandov@fb.com>
> > 
> > ftrace is very quick to give up on saving the task command line (see
> > `trace_save_cmdline()`). The workaround for events which really care
> > about the command line is to explicitly assign it as part of the entry.
> > However, this doesn't work for kprobe events, as there's no
> > straightforward way to get access to current->comm. Add a kprobe/uprobe
> > event variable $comm which provides exactly that.
> > 

Same opinion with Masami; The string_size itself seems not useful IMHO.
Also you can increase 'saved_cmdlines_size' in the tracefs.

Thanks,
Namhyung


> > Signed-off-by: Omar Sandoval <osandov@fb.com>
> > ---
> >  Documentation/trace/kprobetrace.txt  |  4 ++++
> >  Documentation/trace/uprobetracer.txt |  4 ++++
> >  kernel/trace/trace_kprobe.c          |  1 +
> >  kernel/trace/trace_probe.c           | 27 +++++++++++++++++++++++++++
> >  kernel/trace/trace_probe.h           | 10 ++++++++++
> >  5 files changed, 46 insertions(+)
> > 
> > diff --git a/Documentation/trace/kprobetrace.txt b/Documentation/trace/kprobetrace.txt
> > index 4b3f5293b7bf..0bf746656d06 100644
> > --- a/Documentation/trace/kprobetrace.txt
> > +++ b/Documentation/trace/kprobetrace.txt
> > @@ -40,6 +40,7 @@ Synopsis of kprobe_events
> >    $stackN	: Fetch Nth entry of stack (N >= 0)
> >    $stack	: Fetch stack address.
> >    $retval	: Fetch return value.(*)
> > +  $comm		: Fetch current task comm.(***)
> >    +|-offs(FETCHARG) : Fetch memory at FETCHARG +|- offs address.(**)
> >    NAME=FETCHARG : Set NAME as the argument name of FETCHARG.
> >    FETCHARG:TYPE : Set TYPE as the type of FETCHARG. Currently, basic types
> > @@ -48,6 +49,7 @@ Synopsis of kprobe_events
> >  
> >    (*) only for return probe.
> >    (**) this is useful for fetching a field of data structures.
> > +  (***) you probably want this as a string, i.e., $comm:string
> >  
> >  Types
> >  -----
> > @@ -63,6 +65,8 @@ offset, and container-size (usually 32). The syntax is;
> >  
> >   b<bit-width>@<bit-offset>/<container-size>
> >  
> > +For $comm, the type must be either "string" or "string_size".
> 
> Please remove string_size, which is an internal type.

> 
> > +
> >  
> >  Per-Probe Event Filtering
> >  -------------------------
> > diff --git a/Documentation/trace/uprobetracer.txt b/Documentation/trace/uprobetracer.txt
> > index 7e0480263c2f..34754da46860 100644
> > --- a/Documentation/trace/uprobetracer.txt
> > +++ b/Documentation/trace/uprobetracer.txt
> > @@ -36,6 +36,7 @@ Synopsis of uprobe_tracer
> >     $stackN	: Fetch Nth entry of stack (N >= 0)
> >     $stack	: Fetch stack address.
> >     $retval	: Fetch return value.(*)
> > +   $comm	: Fetch current task comm.(***)
> >     +|-offs(FETCHARG) : Fetch memory at FETCHARG +|- offs address.(**)
> >     NAME=FETCHARG     : Set NAME as the argument name of FETCHARG.
> >     FETCHARG:TYPE     : Set TYPE as the type of FETCHARG. Currently, basic types
> > @@ -44,6 +45,7 @@ Synopsis of uprobe_tracer
> >  
> >    (*) only for return probe.
> >    (**) this is useful for fetching a field of data structures.
> > +  (***) you probably want this as a string, i.e., $comm:string
> 
> Ditto.
> 
> Other part looks OK for me :)
> 
> Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
> 
> >  
> >  Types
> >  -----
> > @@ -58,6 +60,8 @@ offset, and container-size (usually 32). The syntax is;
> >  
> >   b<bit-width>@<bit-offset>/<container-size>
> >  
> > +For $comm, the type must be either "string" or "string_size".
> > +
> >  
> >  Event Profiling
> >  ---------------
> > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> > index 5546eec0505f..9aedb0b06683 100644
> > --- a/kernel/trace/trace_kprobe.c
> > +++ b/kernel/trace/trace_kprobe.c
> > @@ -587,6 +587,7 @@ static int create_trace_kprobe(int argc, char **argv)
> >  	 *  $retval	: fetch return value
> >  	 *  $stack	: fetch stack address
> >  	 *  $stackN	: fetch Nth of stack (N:0-)
> > +	 *  $comm       : fetch current task comm
> >  	 *  @ADDR	: fetch memory at ADDR (ADDR should be in kernel)
> >  	 *  @SYM[+|-offs] : fetch memory at SYM +|- offs (SYM is a data symbol)
> >  	 *  %REG	: fetch register REG
> > diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> > index 1d372fa6fefb..3900b6e4a05d 100644
> > --- a/kernel/trace/trace_probe.c
> > +++ b/kernel/trace/trace_probe.c
> > @@ -218,6 +218,28 @@ free_bitfield_fetch_param(struct bitfield_fetch_param *data)
> >  	kfree(data);
> >  }
> >  
> > +void FETCH_FUNC_NAME(comm, string)(struct pt_regs *regs,
> > +					  void *data, void *dest)
> > +{
> > +	int maxlen = get_rloc_len(*(u32 *)dest);
> > +	u8 *dst = get_rloc_data(dest);
> > +	long ret;
> > +
> > +	if (!maxlen)
> > +		return;
> > +
> > +	ret = strlcpy(dst, current->comm, maxlen);
> > +	*(u32 *)dest = make_data_rloc(ret, get_rloc_offs(*(u32 *)dest));
> > +}
> > +NOKPROBE_SYMBOL(FETCH_FUNC_NAME(comm, string));
> > +
> > +void FETCH_FUNC_NAME(comm, string_size)(struct pt_regs *regs,
> > +					       void *data, void *dest)
> > +{
> > +	*(u32 *)dest = strlen(current->comm) + 1;
> > +}
> > +NOKPROBE_SYMBOL(FETCH_FUNC_NAME(comm, string_size));
> > +
> >  static const struct fetch_type *find_fetch_type(const char *type,
> >  						const struct fetch_type *ftbl)
> >  {
> > @@ -348,6 +370,11 @@ static int parse_probe_vars(char *arg, const struct fetch_type *t,
> >  			}
> >  		} else
> >  			ret = -EINVAL;
> > +	} else if (strcmp(arg, "comm") == 0) {
> > +		if (strcmp(t->name, "string") != 0 &&
> > +		    strcmp(t->name, "string_size") != 0)
> > +			return -EINVAL;
> > +		f->fn = t->fetch[FETCH_MTD_comm];
> >  	} else
> >  		ret = -EINVAL;
> >  
> > diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
> > index f6398db09114..45400ca5ded1 100644
> > --- a/kernel/trace/trace_probe.h
> > +++ b/kernel/trace/trace_probe.h
> > @@ -102,6 +102,7 @@ enum {
> >  	FETCH_MTD_reg = 0,
> >  	FETCH_MTD_stack,
> >  	FETCH_MTD_retval,
> > +	FETCH_MTD_comm,
> >  	FETCH_MTD_memory,
> >  	FETCH_MTD_symbol,
> >  	FETCH_MTD_deref,
> > @@ -183,6 +184,14 @@ DECLARE_BASIC_FETCH_FUNCS(bitfield);
> >  #define fetch_bitfield_string			NULL
> >  #define fetch_bitfield_string_size		NULL
> >  
> > +/* comm only makes sense as a string */
> > +#define fetch_comm_u8		NULL
> > +#define fetch_comm_u16		NULL
> > +#define fetch_comm_u32		NULL
> > +#define fetch_comm_u64		NULL
> > +DECLARE_FETCH_FUNC(comm, string);
> > +DECLARE_FETCH_FUNC(comm, string_size);
> > +
> >  /*
> >   * Define macro for basic types - we don't need to define s* types, because
> >   * we have to care only about bitwidth at recording time.
> > @@ -213,6 +222,7 @@ DEFINE_FETCH_##method(u64)
> >  ASSIGN_FETCH_FUNC(reg, ftype),				\
> >  ASSIGN_FETCH_FUNC(stack, ftype),			\
> >  ASSIGN_FETCH_FUNC(retval, ftype),			\
> > +ASSIGN_FETCH_FUNC(comm, ftype),				\
> >  ASSIGN_FETCH_FUNC(memory, ftype),			\
> >  ASSIGN_FETCH_FUNC(symbol, ftype),			\
> >  ASSIGN_FETCH_FUNC(deref, ftype),			\
> > -- 
> > 2.8.3
> > 
> 
> 
> -- 
> Masami Hiramatsu <mhiramat@kernel.org>