1 //===-- ptrace_example.c --------------------------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8
9 #include <asm/ptrace.h>
10 #include <linux/elf.h>
11 #include <stdint.h>
12 #include <stdio.h>
13 #include <sys/prctl.h>
14 #include <sys/ptrace.h>
15 #include <sys/uio.h>
16 #include <sys/wait.h>
17 #include <unistd.h>
18
19 // The demo program shows how to do basic ptrace operations without lldb
20 // or lldb-server. For the purposes of experimentation or reporting bugs
21 // in kernels.
22 //
23 // It is AArch64 Linux specific, adapt as needed.
24 //
25 // Expected output:
26 // Before breakpoint
27 // After breakpoint
28
inferior()29 void inferior() {
30 if (ptrace(PTRACE_TRACEME, 0, 0, 0) < 0) {
31 perror("ptrace");
32 return;
33 }
34
35 printf("Before breakpoint\n");
36
37 // Go into debugger. Instruction replaced with nop later.
38 // We write 2 instuctions because POKETEXT works with
39 // 64 bit values and we don't want to overwrite the
40 // call to printf accidentally.
41 asm volatile("BRK #0 \n nop");
42
43 printf("After breakpoint\n");
44 }
45
debugger(pid_t child)46 void debugger(pid_t child) {
47 int wait_status;
48 // Wait until it hits the breakpoint.
49 wait(&wait_status);
50
51 while (WIFSTOPPED(wait_status)) {
52 if (WIFEXITED(wait_status)) {
53 printf("inferior exited normally\n");
54 return;
55 }
56
57 // Read general purpose registers to find the PC value.
58 struct user_pt_regs regs;
59 struct iovec io;
60 io.iov_base = ®s;
61 io.iov_len = sizeof(regs);
62 if (ptrace(PTRACE_GETREGSET, child, NT_PRSTATUS, &io) < 0) {
63 printf("getregset failed\n");
64 return;
65 }
66
67 // Replace brk #0 / nop with nop / nop by writing to memory
68 // at the current PC.
69 uint64_t replace = 0xd503201fd503201f;
70 if (ptrace(PTRACE_POKETEXT, child, regs.pc, replace) < 0) {
71 printf("replacing bkpt failed\n");
72 return;
73 }
74
75 // Single step over where the brk was.
76 if (ptrace(PTRACE_SINGLESTEP, child, 0, 0) < 0) {
77 perror("ptrace");
78 return;
79 }
80
81 // Wait for single step to be done.
82 wait(&wait_status);
83
84 // Run to completion.
85 if (ptrace(PTRACE_CONT, child, 0, 0) < 0) {
86 perror("ptrace");
87 return;
88 }
89
90 // Wait to see that the inferior exited.
91 wait(&wait_status);
92 }
93 }
94
main()95 int main() {
96 pid_t child = fork();
97
98 if (child == 0)
99 inferior();
100 else if (child > 0)
101 debugger(child);
102 else
103 return -1;
104
105 return 0;
106 }
107