lldb/examples/ptrace_example.c

   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
  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
  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 = &regs;
  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
  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 }