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ftrace: Add sample module that uses register_ftrace_direct()

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Add a sample module that shows a simple use case for
regsiter_ftrace_direct(), and how to use it.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (VMware) 2019-11-08 13:12:33 -05:00
parent 013bf0da04
commit b06457c83a
4 changed files with 57 additions and 0 deletions
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8
samples/Kconfig
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@ -19,6 +19,14 @@ config SAMPLE_TRACE_PRINTK
This builds a module that calls trace_printk() and can be used to
test various trace_printk() calls from a module.
config SAMPLE_FTRACE_DIRECT
tristate "Build register_ftrace_direct() example"
depends on DYNAMIC_FTRACE_WITH_DIRECT_CALLS && m
depends on X86_64 # has x86_64 inlined asm
help
This builds an ftrace direct function example
that hooks to wake_up_process and prints the parameters.
config SAMPLE_KOBJECT
tristate "Build kobject examples"
help

1
samples/Makefile
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@ -17,6 +17,7 @@ obj-$(CONFIG_SAMPLE_RPMSG_CLIENT) += rpmsg/
subdir-$(CONFIG_SAMPLE_SECCOMP) += seccomp
obj-$(CONFIG_SAMPLE_TRACE_EVENTS) += trace_events/
obj-$(CONFIG_SAMPLE_TRACE_PRINTK) += trace_printk/
obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace/
obj-$(CONFIG_VIDEO_PCI_SKELETON) += v4l/
obj-y += vfio-mdev/
subdir-$(CONFIG_SAMPLE_VFS) += vfs

3
samples/ftrace/Makefile Normal file
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@ -0,0 +1,3 @@
# SPDX-License-Identifier: GPL-2.0-only
obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace-direct.o

45
samples/ftrace/ftrace-direct.c Normal file
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@ -0,0 +1,45 @@
// SPDX-License-Identifier: GPL-2.0-only
#include <linux/module.h>
#include <linux/sched.h> /* for wake_up_process() */
#include <linux/ftrace.h>
void my_direct_func(struct task_struct *p)
{
trace_printk("wakeing up %s-%d\n", p->comm, p->pid);
}
extern void my_tramp(void *);
asm (
" .pushsection .text, \"ax\", @progbits\n"
" my_tramp:"
" pushq %rbp\n"
" movq %rsp, %rbp\n"
" pushq %rdi\n"
" call my_direct_func\n"
" popq %rdi\n"
" leave\n"
" ret\n"
" .popsection\n"
);
static int __init ftrace_direct_init(void)
{
return register_ftrace_direct((unsigned long)wake_up_process,
(unsigned long)my_tramp);
}
static void __exit ftrace_direct_exit(void)
{
unregister_ftrace_direct((unsigned long)wake_up_process,
(unsigned long)my_tramp);
}
module_init(ftrace_direct_init);
module_exit(ftrace_direct_exit);
MODULE_AUTHOR("Steven Rostedt");
MODULE_DESCRIPTION("Example use case of using register_ftrace_direct()");
MODULE_LICENSE("GPL");