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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-exception6//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 lldb20// or lldb-server. For the purposes of experimentation or reporting bugs21// in kernels.22//23// It is AArch64 Linux specific, adapt as needed.24//25// Expected output:26// Before breakpoint27// After breakpoint28 29void 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 with39 // 64 bit values and we don't want to overwrite the40 // call to printf accidentally.41 asm volatile("BRK #0 \n nop");42 43 printf("After breakpoint\n");44}45 46void 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 memory68 // 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 95int main() {96 pid_t child = fork();97 98 if (child == 0)99 inferior();100 else if (child > 0)101 debugger(child);102 else103 return -1;104 105 return 0;106}107