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Commit 35abb67d authored by Omar Sandoval's avatar Omar Sandoval Committed by Steven Rostedt
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tracing: expose current->comm to [ku]probe events 

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.

Link: http://lkml.kernel.org/r/f59b472033b943a370f5f48d0af37698f409108f.1465435894.git.osandov@fb.com



Acked-by: default avatarMasami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: default avatarOmar Sandoval <osandov@fb.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 345ddcc8

Documentation/trace/kprobetrace.txt

+3 −0
Original line number Diff line number Diff line
@@ -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
@@ -62,6 +63,8 @@ offset, and container-size (usually 32). The syntax is; 


 b<bit-width>@<bit-offset>/<container-size>



For $comm, the default type is "string"; any other type is invalid.





Per-Probe Event Filtering

-------------------------

Documentation/trace/uprobetracer.txt

+3 −0
Original line number Diff line number Diff line
@@ -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
@@ -57,6 +58,8 @@ offset, and container-size (usually 32). The syntax is; 


 b<bit-width>@<bit-offset>/<container-size>



For $comm, the default type is "string"; any other type is invalid.





Event Profiling

---------------

kernel/trace/trace_kprobe.c

+1 −0
Original line number Diff line number Diff line
@@ -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

kernel/trace/trace_probe.c

+33 −0
Original line number Diff line number Diff line
@@ -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;
@@ -522,6 +549,12 @@ int traceprobe_parse_probe_arg(char *arg, ssize_t *size, 
		arg[t - parg->comm] = '\0';

		t++;

	}

	/*

	 * The default type of $comm should be "string", and it can't be

	 * dereferenced.

	 */

	if (!t && strcmp(arg, "$comm") == 0)

		t = "string";

	parg->type = find_fetch_type(t, ftbl);

	if (!parg->type) {

		pr_info("Unsupported type: %s\n", t);

kernel/trace/trace_probe.h

+10 −0
Original line number Diff line number Diff line
@@ -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),			\