Skip to content

Commit

Permalink
tracing/kprobes: Add $ prefix to special variables
Browse files Browse the repository at this point in the history 
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: Masami 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: Frederic Weisbecker <fweisbec@gmail.com>
  • Loading branch information
Masami Hiramatsu authored and Frederic Weisbecker committed Oct 12, 2009
1 parent 88f70d7 commit 405b265
Show file tree
Hide file tree
Showing 2 changed files with 47 additions and 33 deletions.
20 changes: 10 additions & 10 deletions Documentation/trace/kprobetrace.txt
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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.

Expand Down Expand Up @@ -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.
Expand Down Expand Up @@ -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
Expand Down
60 changes: 37 additions & 23 deletions kernel/trace/trace_kprobe.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -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 */
Expand All @@ -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;
Expand All @@ -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);
Expand All @@ -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
Expand Down Expand Up @@ -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
Expand Down

0 comments on commit 405b265

Please sign in to comment.