[PATCH 3/3] ftrace/samples: Add module to test multi direct modify interface

Jiri Olsa
2021-12-05T23:21:01Z

Adding ftrace-direct-multi-modify.ko kernel module that uses
modify_ftrace_direct_multi API. The core functionality is taken
from ftrace-direct-modify.ko kernel module and changed to fit
multi direct interface.

The init function creates kthread that periodically calls
modify_ftrace_direct_multi to change the trampoline address
for the direct ftrace_ops. The ftrace trace_pipe then shows
trace from both trampolines.

Also adding SAMPLE_FTRACE_MULTI_DIRECT to enable build of
direct multi interface sample modules. It's used in Makefile,
but not defined at the moment.

Same as for ftrace-direct-multi.ko, the new module is enabled
only for x86_64, so there's no need to ifdef the inlined assembly.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
samples/Kconfig | 8 ++
samples/ftrace/Makefile | 1 +
samples/ftrace/ftrace-direct-multi-modify.c | 105 ++++++++++++++++++++
3 files changed, 114 insertions(+)
create mode 100644 samples/ftrace/ftrace-direct-multi-modify.c

diff --git a/samples/Kconfig b/samples/Kconfig
index bec3528aa2de..38daae5a06b5 100644
--- a/samples/Kconfig
+++ b/samples/Kconfig
@@ -31,6 +31,14 @@ config SAMPLE_FTRACE_DIRECT
This builds an ftrace direct function example
that hooks to wake_up_process and prints the parameters.

+config SAMPLE_FTRACE_MULTI_DIRECT
+ tristate "Build register_ftrace_direct_multi() examples"
+ depends on DYNAMIC_FTRACE_WITH_DIRECT_CALLS && m
+ depends on HAVE_SAMPLE_FTRACE_MULTI_DIRECT
+ help
+ This builds an ftrace direct multi function examples
+ that hooks trampolines to multiple functions.
+
config SAMPLE_TRACE_ARRAY
tristate "Build sample module for kernel access to Ftrace instancess"
depends on EVENT_TRACING && m
diff --git a/samples/ftrace/Makefile b/samples/ftrace/Makefile
index e8a3f8520a44..027d375890f8 100644
--- a/samples/ftrace/Makefile
+++ b/samples/ftrace/Makefile
@@ -4,6 +4,7 @@ obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace-direct.o
obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace-direct-too.o
obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace-direct-modify.o
obj-$(CONFIG_SAMPLE_FTRACE_MULTI_DIRECT) += ftrace-direct-multi.o
+obj-$(CONFIG_SAMPLE_FTRACE_MULTI_DIRECT) += ftrace-direct-multi-modify.o

CFLAGS_sample-trace-array.o := -I$(src)
obj-$(CONFIG_SAMPLE_TRACE_ARRAY) += sample-trace-array.o
diff --git a/samples/ftrace/ftrace-direct-multi-modify.c b/samples/ftrace/ftrace-direct-multi-modify.c
new file mode 100644
index 000000000000..ba309cb33c77
--- /dev/null
+++ b/samples/ftrace/ftrace-direct-multi-modify.c
@@ -0,0 +1,105 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/module.h>
+#include <linux/kthread.h>
+#include <linux/ftrace.h>
+
+void my_direct_func1(unsigned long ip)
+{
+ trace_printk("my direct func1 ip %lx\n", ip);
+}
+
+void my_direct_func2(unsigned long ip)
+{
+ trace_printk("my direct func2 ip %lx\n", ip);
+}
+
+extern void my_tramp1(void *);
+extern void my_tramp2(void *);
+
+asm (
+" .pushsection .text, \"ax\", @progbits\n"
+" .type my_tramp1, @function\n"
+" .globl my_tramp1\n"
+" my_tramp1:"
+" pushq %rbp\n"
+" movq %rsp, %rbp\n"
+" pushq %rdi\n"
+" movq 8(%rbp), %rdi\n"
+" call my_direct_func1\n"
+" popq %rdi\n"
+" leave\n"
+" ret\n"
+" .size my_tramp1, .-my_tramp1\n"
+" .type my_tramp2, @function\n"
+"\n"
+" .globl my_tramp2\n"
+" my_tramp2:"
+" pushq %rbp\n"
+" movq %rsp, %rbp\n"
+" pushq %rdi\n"
+" movq 8(%rbp), %rdi\n"
+" call my_direct_func2\n"
+" popq %rdi\n"
+" leave\n"
+" ret\n"
+" .size my_tramp2, .-my_tramp2\n"
+" .popsection\n"
+);
+
+static unsigned long my_tramp = (unsigned long)my_tramp1;
+static unsigned long tramps[2] = {
+ (unsigned long)my_tramp1,
+ (unsigned long)my_tramp2,
+};
+
+static struct ftrace_ops direct;
+
+static int simple_thread(void *arg)
+{
+ static int t;
+ int ret = 0;
+
+ while (!kthread_should_stop()) {
+ set_current_state(TASK_INTERRUPTIBLE);
+ schedule_timeout(2 * HZ);
+
+ if (ret)
+ continue;
+ t ^= 1;
+ ret = modify_ftrace_direct_multi(&direct, tramps[t]);
+ if (!ret)
+ my_tramp = tramps[t];
+ WARN_ON_ONCE(ret);
+ }
+
+ return 0;
+}
+
+static struct task_struct *simple_tsk;
+
+static int __init ftrace_direct_multi_init(void)
+{
+ int ret;
+
+ ftrace_set_filter_ip(&direct, (unsigned long) wake_up_process, 0, 0);
+ ftrace_set_filter_ip(&direct, (unsigned long) schedule, 0, 0);
+
+ ret = register_ftrace_direct_multi(&direct, my_tramp);
+
+ if (!ret)
+ simple_tsk = kthread_run(simple_thread, NULL, "event-sample-fn");
+ return ret;
+}
+
+static void __exit ftrace_direct_multi_exit(void)
+{
+ kthread_stop(simple_tsk);
+ unregister_ftrace_direct_multi(&direct, my_tramp);
+}
+
+module_init(ftrace_direct_multi_init);
+module_exit(ftrace_direct_multi_exit);
+
+MODULE_AUTHOR("Jiri Olsa");
+MODULE_DESCRIPTION("Example use case of using modify_ftrace_direct_multi()");
+MODULE_LICENSE("GPL");
--
2.33.1