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Subject[PATCH -tip 2/8] tracing/kprobe: Drop function argument access syntax
Date
Drop function argument access syntax, because the function arguments
are depends on not only architecture but also compile-options and
function API. And now, we have perf-probe for finding register/memory
assigned to each argument.

Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Roland McGrath <roland@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Michael Neuling <mikey@neuling.org>
Cc: linuxppc-dev@ozlabs.org
---

Documentation/trace/kprobetrace.txt | 21 ++++++++++-----------
kernel/trace/trace_kprobe.c | 18 +-----------------
2 files changed, 11 insertions(+), 28 deletions(-)

diff --git a/Documentation/trace/kprobetrace.txt b/Documentation/trace/kprobetrace.txt
index c3eff6f..f30978e 100644
--- a/Documentation/trace/kprobetrace.txt
+++ b/Documentation/trace/kprobetrace.txt
@@ -37,15 +37,12 @@ Synopsis of kprobe_events
@SYM[+|-offs] : Fetch memory at SYM +|- offs (SYM should be a data symbol)
$stackN : Fetch Nth entry of stack (N >= 0)
$stack : Fetch stack address.
- $argN : Fetch function argument. (N >= 0)(*)
- $retval : Fetch return value.(**)
- +|-offs(FETCHARG) : Fetch memory at FETCHARG +|- offs address.(***)
+ $retval : Fetch return value.(*)
+ +|-offs(FETCHARG) : Fetch memory at FETCHARG +|- offs address.(**)
NAME=FETCHARG: Set NAME as the argument name of FETCHARG.

- (*) aN may not correct on asmlinkaged functions and at the middle of
- function body.
- (**) only for return probe.
- (***) this is useful for fetching a field of data structures.
+ (*) only for return probe.
+ (**) this is useful for fetching a field of data structures.


Per-Probe Event Filtering
@@ -82,11 +79,14 @@ 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=$arg0 filename=$arg1 flags=$arg2 mode=$arg3 > /sys/kernel/debug/tracing/kprobe_events
+ echo p:myprobe do_sys_open dfd=%ax filename=%dx flags=%cx mode=+4($stack) > /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.
+1st to 4th arguments as "myprobe" event. Note, which register/stack entry is
+assigned to each function argument depends on arch-specific ABI. If you unsure
+the ABI, please try to use probe subcommand of perf-tools (you can find it
+under tools/perf/).
+As this example shows, users can choose more familiar names for each arguments.

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

@@ -147,4 +147,3 @@ events, you need to enable it.
returns from SYMBOL(e.g. "sys_open+0x1b/0x1d <- do_sys_open" means kernel
returns from do_sys_open to sys_open+0x1b).

-
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 47f54ab..7ac728d 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -91,11 +91,6 @@ static __kprobes unsigned long fetch_memory(struct pt_regs *regs, void *addr)
return retval;
}

-static __kprobes unsigned long fetch_argument(struct pt_regs *regs, void *num)
-{
- return regs_get_argument_nth(regs, (unsigned int)((unsigned long)num));
-}
-
static __kprobes unsigned long fetch_retvalue(struct pt_regs *regs,
void *dummy)
{
@@ -231,9 +226,7 @@ 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, "$arg%lu", (unsigned long)ff->data);
- else if (ff->func == fetch_register) {
+ if (ff->func == fetch_register) {
const char *name;
name = regs_query_register_name((unsigned int)((long)ff->data));
ret = snprintf(buf, n, "%%%s", name);
@@ -489,14 +482,6 @@ static int parse_probe_vars(char *arg, struct fetch_func *ff, int is_return)
}
} else
ret = -EINVAL;
- } else if (strncmp(arg, "arg", 3) == 0 && isdigit(arg[3])) {
- ret = strict_strtoul(arg + 3, 10, &param);
- if (ret || param > PARAM_MAX_ARGS)
- ret = -EINVAL;
- else {
- ff->func = fetch_argument;
- ff->data = (void *)param;
- }
} else
ret = -EINVAL;
return ret;
@@ -611,7 +596,6 @@ 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:
- * $argN : fetch Nth of function argument. (N:0-)
* $retval : fetch return value
* $stack : fetch stack address
* $stackN : fetch Nth of stack (N:0-)

--
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com


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