Commit 405b2651 authored by Masami Hiramatsu's avatar Masami Hiramatsu Committed by Frederic Weisbecker
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tracing/kprobes: Add $ prefix to special variables 



Add $ prefix to the special variables(e.g. sa, rv) of kprobe-tracer.
This resolves consistency issues between kprobe_events and perf-kprobe.

The main goal is to avoid conflicts between local variable names of
probed functions, used by perf probe, and special variables used
in the kprobe event creation interface (stack values, etc...) and
also available from perf probe.

ie: we don't want rv (return value) to conflict with a local variable
named rv in a probed function.

Signed-off-by: default avatarMasami Hiramatsu <mhiramat@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Jim Keniston <jkenisto@us.ibm.com>
Cc: Frank Ch. Eigler <fche@redhat.com>
LKML-Reference: <20091007222740.1684.91170.stgit@dhcp-100-2-132.bos.redhat.com>
Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
parent 88f70d75

Documentation/trace/kprobetrace.txt

+10 −10
Original line number Diff line number Diff line
@@ -36,13 +36,13 @@ Synopsis of kprobe_events 


 FETCHARGS	: Arguments. Each probe can have up to 128 args.

  %REG	: Fetch register REG

  sN	: Fetch Nth entry of stack (N >= 0)

  sa	: Fetch stack address.

  @ADDR	: Fetch memory at ADDR (ADDR should be in kernel)

  @SYM[+|-offs]	: Fetch memory at SYM +|- offs (SYM should be a data symbol)

  aN	: Fetch function argument. (N >= 0)(*)

  rv	: Fetch return value.(**)

  ra	: Fetch return address.(**)

  $sN	: Fetch Nth entry of stack (N >= 0)

  $sa	: Fetch stack address.

  $aN	: Fetch function argument. (N >= 0)(*)

  $rv	: Fetch return value.(**)

  $ra	: Fetch return address.(**)

  +|-offs(FETCHARG) : Fetch memory at FETCHARG +|- offs address.(***)

  NAME=FETCHARG: Set NAME as the argument name of FETCHARG.
@@ -85,13 +85,13 @@ Usage examples 
To add a probe as a new event, write a new definition to kprobe_events

as below.



  echo p:myprobe do_sys_open dfd=a0 filename=a1 flags=a2 mode=a3 > /sys/kernel/debug/tracing/kprobe_events

  echo p:myprobe do_sys_open dfd=$a0 filename=$a1 flags=$a2 mode=$a3 > /sys/kernel/debug/tracing/kprobe_events



 This sets a kprobe on the top of do_sys_open() function with recording

1st to 4th arguments as "myprobe" event. As this example shows, users can

choose more familiar names for each arguments.



  echo r:myretprobe do_sys_open rv ra >> /sys/kernel/debug/tracing/kprobe_events

  echo r:myretprobe do_sys_open $rv $ra >> /sys/kernel/debug/tracing/kprobe_events



 This sets a kretprobe on the return point of do_sys_open() function with

recording return value and return address as "myretprobe" event.
@@ -138,11 +138,11 @@ events, you need to enable it. 
#           TASK-PID    CPU#    TIMESTAMP  FUNCTION

#              | |       |          |         |

           <...>-1447  [001] 1038282.286875: myprobe: (do_sys_open+0x0/0xd6) dfd=3 filename=7fffd1ec4440 flags=8000 mode=0

           <...>-1447  [001] 1038282.286878: myretprobe: (sys_openat+0xc/0xe <- do_sys_open) rv=fffffffffffffffe ra=ffffffff81367a3a

           <...>-1447  [001] 1038282.286878: myretprobe: (sys_openat+0xc/0xe <- do_sys_open) $rv=fffffffffffffffe $ra=ffffffff81367a3a

           <...>-1447  [001] 1038282.286885: myprobe: (do_sys_open+0x0/0xd6) dfd=ffffff9c filename=40413c flags=8000 mode=1b6

           <...>-1447  [001] 1038282.286915: myretprobe: (sys_open+0x1b/0x1d <- do_sys_open) rv=3 ra=ffffffff81367a3a

           <...>-1447  [001] 1038282.286915: myretprobe: (sys_open+0x1b/0x1d <- do_sys_open) $rv=3 $ra=ffffffff81367a3a

           <...>-1447  [001] 1038282.286969: myprobe: (do_sys_open+0x0/0xd6) dfd=ffffff9c filename=4041c6 flags=98800 mode=10

           <...>-1447  [001] 1038282.286976: myretprobe: (sys_open+0x1b/0x1d <- do_sys_open) rv=3 ra=ffffffff81367a3a

           <...>-1447  [001] 1038282.286976: myretprobe: (sys_open+0x1b/0x1d <- do_sys_open) $rv=3 $ra=ffffffff81367a3a





 Each line shows when the kernel hits an event, and <- SYMBOL means kernel

kernel/trace/trace_kprobe.c

+37 −23
Original line number Diff line number Diff line
@@ -220,24 +220,24 @@ static int probe_arg_string(char *buf, size_t n, struct fetch_func *ff) 
	int ret = -EINVAL;



	if (ff->func == fetch_argument)

		ret = snprintf(buf, n, "a%lu", (unsigned long)ff->data);

		ret = snprintf(buf, n, "$a%lu", (unsigned long)ff->data);

	else if (ff->func == fetch_register) {

		const char *name;

		name = regs_query_register_name((unsigned int)((long)ff->data));

		ret = snprintf(buf, n, "%%%s", name);

	} else if (ff->func == fetch_stack)

		ret = snprintf(buf, n, "s%lu", (unsigned long)ff->data);

		ret = snprintf(buf, n, "$s%lu", (unsigned long)ff->data);

	else if (ff->func == fetch_memory)

		ret = snprintf(buf, n, "@0x%p", ff->data);

	else if (ff->func == fetch_symbol) {

		struct symbol_cache *sc = ff->data;

		ret = snprintf(buf, n, "@%s%+ld", sc->symbol, sc->offset);

	} else if (ff->func == fetch_retvalue)

		ret = snprintf(buf, n, "rv");

		ret = snprintf(buf, n, "$rv");

	else if (ff->func == fetch_ip)

		ret = snprintf(buf, n, "ra");

		ret = snprintf(buf, n, "$ra");

	else if (ff->func == fetch_stack_address)

		ret = snprintf(buf, n, "sa");

		ret = snprintf(buf, n, "$sa");

	else if (ff->func == fetch_indirect) {

		struct indirect_fetch_data *id = ff->data;

		size_t l = 0;
@@ -429,12 +429,10 @@ static int split_symbol_offset(char *symbol, unsigned long *offset) 
#define PARAM_MAX_ARGS 16

#define PARAM_MAX_STACK (THREAD_SIZE / sizeof(unsigned long))



static int parse_probe_arg(char *arg, struct fetch_func *ff, int is_return)

static int parse_probe_vars(char *arg, struct fetch_func *ff, int is_return)

{

	int ret = 0;

	unsigned long param;

	long offset;

	char *tmp;



	switch (arg[0]) {

	case 'a':	/* argument */
@@ -456,14 +454,6 @@ static int parse_probe_arg(char *arg, struct fetch_func *ff, int is_return) 
		} else

			ret = -EINVAL;

		break;

	case '%':	/* named register */

		ret = regs_query_register_offset(arg + 1);

		if (ret >= 0) {

			ff->func = fetch_register;

			ff->data = (void *)(unsigned long)ret;

			ret = 0;

		}

		break;

	case 's':	/* stack */

		if (arg[1] == 'a') {

			ff->func = fetch_stack_address;
@@ -478,6 +468,31 @@ static int parse_probe_arg(char *arg, struct fetch_func *ff, int is_return) 
			}

		}

		break;

	default:

		ret = -EINVAL;

	}

	return ret;

}



static int parse_probe_arg(char *arg, struct fetch_func *ff, int is_return)

{

	int ret = 0;

	unsigned long param;

	long offset;

	char *tmp;



	switch (arg[0]) {

	case '$':

		ret = parse_probe_vars(arg + 1, ff, is_return);

		break;

	case '%':	/* named register */

		ret = regs_query_register_offset(arg + 1);

		if (ret >= 0) {

			ff->func = fetch_register;

			ff->data = (void *)(unsigned long)ret;

			ret = 0;

		}

		break;

	case '@':	/* memory or symbol */

		if (isdigit(arg[1])) {

			ret = strict_strtoul(arg + 1, 0, &param);
@@ -489,8 +504,7 @@ static int parse_probe_arg(char *arg, struct fetch_func *ff, int is_return) 
			ret = split_symbol_offset(arg + 1, &offset);

			if (ret)

				break;

			ff->data = alloc_symbol_cache(arg + 1,

							      offset);

			ff->data = alloc_symbol_cache(arg + 1, offset);

			if (ff->data)

				ff->func = fetch_symbol;

			else
@@ -544,11 +558,11 @@ static int create_trace_probe(int argc, char **argv) 
	 *  - Add kprobe: p[:[GRP/]EVENT] KSYM[+OFFS]|KADDR [FETCHARGS]

	 *  - Add kretprobe: r[:[GRP/]EVENT] KSYM[+0] [FETCHARGS]

	 * Fetch args:

	 *  aN	: fetch Nth of function argument. (N:0-)

	 *  rv	: fetch return value

	 *  ra	: fetch return address

	 *  sa	: fetch stack address

	 *  sN	: fetch Nth of stack (N:0-)

	 *  $aN	: fetch Nth of function argument. (N:0-)

	 *  $rv	: fetch return value

	 *  $ra	: fetch return address

	 *  $sa	: fetch stack address

	 *  $sN	: fetch Nth of stack (N:0-)

	 *  @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

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