tracing/kprobes: Fix kprobe-tracer to support stack trace

Fix to support kernel stack trace correctly on kprobe-tracer.
Since the execution path of kprobe-based dynamic events is different
from other tracepoint-based events, normal ftrace_trace_stack() doesn't
work correctly. To fix that, this introduces ftrace_trace_stack_regs()
which traces stack via pt_regs instead of current stack register.

e.g.

 # echo p schedule+4 > /sys/kernel/debug/tracing/kprobe_events
 # echo 1 > /sys/kernel/debug/tracing/options/stacktrace
 # echo 1 > /sys/kernel/debug/tracing/events/kprobes/enable
 # head -n 20 /sys/kernel/debug/tracing/trace
            bash-2968  [000] 10297.050245: p_schedule_4: (schedule+0x4/0x4ca)
            bash-2968  [000] 10297.050247: <stack trace>
 => schedule_timeout
 => n_tty_read
 => tty_read
 => vfs_read
 => sys_read
 => system_call_fastpath
     kworker/0:1-2940  [000] 10297.050265: p_schedule_4: (schedule+0x4/0x4ca)
     kworker/0:1-2940  [000] 10297.050266: <stack trace>
 => worker_thread
 => kthread
 => kernel_thread_helper
            sshd-1132  [000] 10297.050365: p_schedule_4: (schedule+0x4/0x4ca)
            sshd-1132  [000] 10297.050365: <stack trace>
 => sysret_careful

Note: Even with this fix, the first entry will be skipped
if the probe is put on the function entry area before
the frame pointer is set up (usually, that is 4 bytes
 (push %bp; mov %sp %bp) on x86), because stack unwinder
depends on the frame pointer.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: yrl.pp-manager.tt@hitachi.com
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Namhyung Kim <namhyung@gmail.com>
Link: http://lkml.kernel.org/r/20110608070934.17777.17116.stgit@fedora15
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index f925c45f0afa..7053ef3d73d2 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -1397,7 +1397,8 @@ static __kprobes void kprobe_trace_func(struct kprobe *kp, struct pt_regs *regs)
         store_trace_args(sizeof(*entry), tp, regs, (u8 *)&entry[1], dsize);
 
         if (!filter_current_check_discard(buffer, call, entry, event))
-                trace_nowake_buffer_unlock_commit(buffer, event, irq_flags, pc);
+                trace_nowake_buffer_unlock_commit_regs(buffer, event,
+                                                       irq_flags, pc, regs);
 }
 
 /* Kretprobe handler */
@@ -1429,7 +1430,8 @@ static __kprobes void kretprobe_trace_func(struct kretprobe_instance *ri,
         store_trace_args(sizeof(*entry), tp, regs, (u8 *)&entry[1], dsize);
 
         if (!filter_current_check_discard(buffer, call, entry, event))
-                trace_nowake_buffer_unlock_commit(buffer, event, irq_flags, pc);
+                trace_nowake_buffer_unlock_commit_regs(buffer, event,
+                                                       irq_flags, pc, regs);
 }
 
 /* Event entry printers */