samples/ftrace/ftrace-direct-modify.c

0001 // SPDX-License-Identifier: GPL-2.0-only
0002 #include <linux/module.h>
0003 #include <linux/kthread.h>
0004 #include <linux/ftrace.h>
0005 #include <asm/asm-offsets.h>
0006
0007 extern void my_direct_func1(void);
0008 extern void my_direct_func2(void);
0009
0010 void my_direct_func1(void)
0011 {
0012     trace_printk("my direct func1\n");
0013 }
0014
0015 void my_direct_func2(void)
0016 {
0017     trace_printk("my direct func2\n");
0018 }
0019
0020 extern void my_tramp1(void *);
0021 extern void my_tramp2(void *);
0022
0023 static unsigned long my_ip = (unsigned long)schedule;
0024
0025 #ifdef CONFIG_X86_64
0026
0027 #include <asm/ibt.h>
0028
0029 asm (
0030 "   .pushsection    .text, \"ax\", @progbits\n"
0031 "   .type       my_tramp1, @function\n"
0032 "   .globl      my_tramp1\n"
0033 "   my_tramp1:"
0034     ASM_ENDBR
0035 "   pushq %rbp\n"
0036 "   movq %rsp, %rbp\n"
0037 "   call my_direct_func1\n"
0038 "   leave\n"
0039 "   .size       my_tramp1, .-my_tramp1\n"
0040     ASM_RET
0041
0042 "   .type       my_tramp2, @function\n"
0043 "   .globl      my_tramp2\n"
0044 "   my_tramp2:"
0045     ASM_ENDBR
0046 "   pushq %rbp\n"
0047 "   movq %rsp, %rbp\n"
0048 "   call my_direct_func2\n"
0049 "   leave\n"
0050     ASM_RET
0051 "   .size       my_tramp2, .-my_tramp2\n"
0052 "   .popsection\n"
0053 );
0054
0055 #endif /* CONFIG_X86_64 */
0056
0057 #ifdef CONFIG_S390
0058
0059 asm (
0060 "   .pushsection    .text, \"ax\", @progbits\n"
0061 "   .type       my_tramp1, @function\n"
0062 "   .globl      my_tramp1\n"
0063 "   my_tramp1:"
0064 "   lgr     %r1,%r15\n"
0065 "   stmg        %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
0066 "   stg     %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
0067 "   aghi        %r15,"__stringify(-STACK_FRAME_OVERHEAD)"\n"
0068 "   stg     %r1,"__stringify(__SF_BACKCHAIN)"(%r15)\n"
0069 "   brasl       %r14,my_direct_func1\n"
0070 "   aghi        %r15,"__stringify(STACK_FRAME_OVERHEAD)"\n"
0071 "   lmg     %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
0072 "   lg      %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
0073 "   lgr     %r1,%r0\n"
0074 "   br      %r1\n"
0075 "   .size       my_tramp1, .-my_tramp1\n"
0076 "   .type       my_tramp2, @function\n"
0077 "   .globl      my_tramp2\n"
0078 "   my_tramp2:"
0079 "   lgr     %r1,%r15\n"
0080 "   stmg        %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
0081 "   stg     %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
0082 "   aghi        %r15,"__stringify(-STACK_FRAME_OVERHEAD)"\n"
0083 "   stg     %r1,"__stringify(__SF_BACKCHAIN)"(%r15)\n"
0084 "   brasl       %r14,my_direct_func2\n"
0085 "   aghi        %r15,"__stringify(STACK_FRAME_OVERHEAD)"\n"
0086 "   lmg     %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
0087 "   lg      %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
0088 "   lgr     %r1,%r0\n"
0089 "   br      %r1\n"
0090 "   .size       my_tramp2, .-my_tramp2\n"
0091 "   .popsection\n"
0092 );
0093
0094 #endif /* CONFIG_S390 */
0095
0096 static unsigned long my_tramp = (unsigned long)my_tramp1;
0097 static unsigned long tramps[2] = {
0098     (unsigned long)my_tramp1,
0099     (unsigned long)my_tramp2,
0100 };
0101
0102 static int simple_thread(void *arg)
0103 {
0104     static int t;
0105     int ret = 0;
0106
0107     while (!kthread_should_stop()) {
0108         set_current_state(TASK_INTERRUPTIBLE);
0109         schedule_timeout(2 * HZ);
0110
0111         if (ret)
0112             continue;
0113         t ^= 1;
0114         ret = modify_ftrace_direct(my_ip, my_tramp, tramps[t]);
0115         if (!ret)
0116             my_tramp = tramps[t];
0117         WARN_ON_ONCE(ret);
0118     }
0119
0120     return 0;
0121 }
0122
0123 static struct task_struct *simple_tsk;
0124
0125 static int __init ftrace_direct_init(void)
0126 {
0127     int ret;
0128
0129     ret = register_ftrace_direct(my_ip, my_tramp);
0130     if (!ret)
0131         simple_tsk = kthread_run(simple_thread, NULL, "event-sample-fn");
0132     return ret;
0133 }
0134
0135 static void __exit ftrace_direct_exit(void)
0136 {
0137     kthread_stop(simple_tsk);
0138     unregister_ftrace_direct(my_ip, my_tramp);
0139 }
0140
0141 module_init(ftrace_direct_init);
0142 module_exit(ftrace_direct_exit);
0143
0144 MODULE_AUTHOR("Steven Rostedt");
0145 MODULE_DESCRIPTION("Example use case of using modify_ftrace_direct()");
0146 MODULE_LICENSE("GPL");