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ftrace-direct-modify.c
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// SPDX-License-Identifier: GPL-2.0-only
#include <linux/module.h>
#include <linux/kthread.h>
#include <linux/ftrace.h>
#include <asm/asm-offsets.h>
extern void my_direct_func1(void);
extern void my_direct_func2(void);
void my_direct_func1(void)
{
trace_printk("my direct func1\n");
}
void my_direct_func2(void)
{
trace_printk("my direct func2\n");
}
extern void my_tramp1(void *);
extern void my_tramp2(void *);
static unsigned long my_ip = (unsigned long)schedule;
#ifdef CONFIG_X86_64
#include <asm/ibt.h>
asm (
" .pushsection .text, \"ax\", @progbits\n"
" .type my_tramp1, @function\n"
" .globl my_tramp1\n"
" my_tramp1:"
ASM_ENDBR
" pushq %rbp\n"
" movq %rsp, %rbp\n"
" call my_direct_func1\n"
" leave\n"
" .size my_tramp1, .-my_tramp1\n"
ASM_RET
" .type my_tramp2, @function\n"
" .globl my_tramp2\n"
" my_tramp2:"
ASM_ENDBR
" pushq %rbp\n"
" movq %rsp, %rbp\n"
" call my_direct_func2\n"
" leave\n"
ASM_RET
" .size my_tramp2, .-my_tramp2\n"
" .popsection\n"
);
#endif /* CONFIG_X86_64 */
#ifdef CONFIG_S390
asm (
" .pushsection .text, \"ax\", @progbits\n"
" .type my_tramp1, @function\n"
" .globl my_tramp1\n"
" my_tramp1:"
" lgr %r1,%r15\n"
" stmg %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
" stg %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
" aghi %r15,"__stringify(-STACK_FRAME_OVERHEAD)"\n"
" stg %r1,"__stringify(__SF_BACKCHAIN)"(%r15)\n"
" brasl %r14,my_direct_func1\n"
" aghi %r15,"__stringify(STACK_FRAME_OVERHEAD)"\n"
" lmg %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
" lg %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
" lgr %r1,%r0\n"
" br %r1\n"
" .size my_tramp1, .-my_tramp1\n"
" .type my_tramp2, @function\n"
" .globl my_tramp2\n"
" my_tramp2:"
" lgr %r1,%r15\n"
" stmg %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
" stg %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
" aghi %r15,"__stringify(-STACK_FRAME_OVERHEAD)"\n"
" stg %r1,"__stringify(__SF_BACKCHAIN)"(%r15)\n"
" brasl %r14,my_direct_func2\n"
" aghi %r15,"__stringify(STACK_FRAME_OVERHEAD)"\n"
" lmg %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
" lg %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
" lgr %r1,%r0\n"
" br %r1\n"
" .size my_tramp2, .-my_tramp2\n"
" .popsection\n"
);
#endif /* CONFIG_S390 */
static unsigned long my_tramp = (unsigned long)my_tramp1;
static unsigned long tramps[2] = {
(unsigned long)my_tramp1,
(unsigned long)my_tramp2,
};
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(my_ip, my_tramp, 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_init(void)
{
int ret;
ret = register_ftrace_direct(my_ip, my_tramp);
if (!ret)
simple_tsk = kthread_run(simple_thread, NULL, "event-sample-fn");
return ret;
}
static void __exit ftrace_direct_exit(void)
{
kthread_stop(simple_tsk);
unregister_ftrace_direct(my_ip, my_tramp);
}
module_init(ftrace_direct_init);
module_exit(ftrace_direct_exit);
MODULE_AUTHOR("Steven Rostedt");
MODULE_DESCRIPTION("Example use case of using modify_ftrace_direct()");
MODULE_LICENSE("GPL");