[PATCH] trace-cmd: add plugin for decoding syscalls/sys_enter_futex

[Julia Cartwright]

The futex syscall is a complicated one.  It supports thirteen
multiplexed operations, each with different semantics and encodings for
the syscalls six arguments.

Manually decoding these arguments is tedious and error prone.

This plugin provides symbolic names for futex operations, futex flags,
and tries to be intelligent about the intent of specific arguments (for
example, waking operations use 'val' as an integer count, not just an
arbitrary value).

It doesn't do a full decode of the FUTEX_WAKE_OP's 'val3' argument,
however, this is a good starting point.

Signed-off-by: Julia Cartwright <julia@xxxxxx>
---
 Makefile       |   1 +
 plugin_futex.c | 135 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 136 insertions(+)
 create mode 100644 plugin_futex.c

diff --git a/Makefile b/Makefile
index 5c35143c8867..58b957d9a578 100644
--- a/Makefile
+++ b/Makefile
@@ -365,6 +365,7 @@ PLUGIN_OBJS += plugin_kvm.o
 PLUGIN_OBJS += plugin_mac80211.o
 PLUGIN_OBJS += plugin_sched_switch.o
 PLUGIN_OBJS += plugin_function.o
+PLUGIN_OBJS += plugin_futex.o
 PLUGIN_OBJS += plugin_xen.o
 PLUGIN_OBJS += plugin_scsi.o
 PLUGIN_OBJS += plugin_cfg80211.o
diff --git a/plugin_futex.c b/plugin_futex.c
new file mode 100644
index 000000000000..b12c92d91a86
--- /dev/null
+++ b/plugin_futex.c
@@ -0,0 +1,135 @@
+/*
+ * Copyright (C) 2017 National Instruments Corp.
+ *
+ * Author: Julia Cartwright <julia@xxxxxx>
+ *
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation;
+ * version 2.1 of the License (not later!)
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this program; if not,  see <http://www.gnu.org/licenses>
+ *
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <linux/futex.h>
+
+#include "trace-cmd.h"
+
+struct futex_args {
+	unsigned long long	uaddr;
+	unsigned long long	op;
+	unsigned long long	val;
+	unsigned long long	utime; /* or val2 */
+	unsigned long long	uaddr2;
+	unsigned long long	val3;
+};
+
+struct futex_op {
+	const char	*name;
+	const char	*fmt_val;
+	const char	*fmt_utime;
+	const char	*fmt_uaddr2;
+	const char	*fmt_val3;
+};
+
+static const struct futex_op futex_op_tbl[] = {
+	{            "FUTEX_WAIT", " val=0x%08llx", " utime=0x%08llx",               NULL,             NULL },
+	{            "FUTEX_WAKE",     " val=%llu",              NULL,               NULL,             NULL },
+	{              "FUTEX_FD",     " val=%llu",              NULL,               NULL,             NULL },
+	{         "FUTEX_REQUEUE",     " val=%llu",      " val2=%llu", " uaddr2=0x%08llx",             NULL },
+	{     "FUTEX_CMP_REQUEUE",     " val=%llu",      " val2=%llu", " uaddr2=0x%08llx", " val3=0x%08llx" },
+	{         "FUTEX_WAKE_OP",     " val=%llu",      " val2=%llu", " uaddr2=0x%08llx", " val3=0x%08llx" },
+	{         "FUTEX_LOCK_PI",            NULL, " utime=0x%08llx",               NULL,             NULL },
+	{       "FUTEX_UNLOCK_PI",            NULL,              NULL,               NULL,             NULL },
+	{      "FUTEX_TRYLOCK_PI",            NULL,              NULL,               NULL,             NULL },
+	{     "FUTEX_WAIT_BITSET", " val=0x%08llx", " utime=0x%08llx",               NULL, " val3=0x%08llx" },
+	{     "FUTEX_WAKE_BITSET",     " val=%llu",              NULL,               NULL, " val3=0x%08llx" },
+	{ "FUTEX_WAIT_REQUEUE_PI", " val=0x%08llx", " utime=0x%08llx", " uaddr2=0x%08llx", " val3=0x%08llx" },
+	{  "FUTEX_CMP_REQUEUE_PI",     " val=%llu",      " val2=%llu", " uaddr2=0x%08llx", " val3=0x%08llx" },
+};
+
+
+static void futex_print(struct trace_seq *s, const struct futex_args *args,
+			const struct futex_op *fop)
+{
+	trace_seq_printf(s, " uaddr=0x%08llx", args->uaddr);
+
+	if (fop->fmt_val)
+		trace_seq_printf(s, fop->fmt_val, args->val);
+
+	if (fop->fmt_utime)
+		trace_seq_printf(s,fop->fmt_utime, args->utime);
+
+	if (fop->fmt_uaddr2)
+		trace_seq_printf(s, fop->fmt_uaddr2, args->uaddr2);
+
+	if (fop->fmt_val3)
+		trace_seq_printf(s, fop->fmt_val3, args->val3);
+}
+
+static int futex_handler(struct trace_seq *s, struct pevent_record *record,
+			 struct event_format *event, void *context)
+{
+	const struct futex_op *fop;
+	struct futex_args args;
+	unsigned long long cmd;
+
+	if (pevent_get_field_val(s, event, "uaddr", record, &args.uaddr, 1))
+		return 1;
+
+	if (pevent_get_field_val(s, event, "op", record, &args.op, 1))
+		return 1;
+
+	if (pevent_get_field_val(s, event, "val", record, &args.val, 1))
+		return 1;
+
+	if (pevent_get_field_val(s, event, "utime", record, &args.utime, 1))
+		return 1;
+
+	if (pevent_get_field_val(s, event, "uaddr2", record, &args.uaddr2, 1))
+		return 1;
+
+	if (pevent_get_field_val(s, event, "val3", record, &args.val3, 1))
+		return 1;
+
+	cmd = args.op & FUTEX_CMD_MASK;
+	if (cmd >= ARRAY_SIZE(futex_op_tbl))
+		return 1;
+
+	fop = &futex_op_tbl[cmd];
+
+	trace_seq_printf(s, "op=%s", fop->name);
+
+	if (args.op & FUTEX_PRIVATE_FLAG)
+		trace_seq_puts(s, "|FUTEX_PRIVATE_FLAG");
+
+	if (args.op & FUTEX_CLOCK_REALTIME)
+		trace_seq_puts(s, "|FUTEX_CLOCK_REALTIME");
+
+	futex_print(s, &args, fop);
+	return 0;
+}
+
+int PEVENT_PLUGIN_LOADER(struct pevent *pevent)
+{
+	pevent_register_event_handler(pevent, -1, "syscalls", "sys_enter_futex",
+				      futex_handler, NULL);
+	return 0;
+}
+
+void PEVENT_PLUGIN_UNLOADER(struct pevent *pevent)
+{
+	pevent_unregister_event_handler(pevent, -1, "syscalls", "sys_enter_futex",
+					futex_handler, NULL);
+}
-- 
2.14.2