【发布时间】：2014-04-17 11:21:29
【问题描述】：
我正在尝试按照this guide 设置断点来实现相同的结果，唯一的区别是我使用的是 x64 系统。所以，我有这个“Hello, World!”的代码：
; The _start symbol must be declared for the linker (ld)
global _start
section .text
_start:
; Prepare arguments for the sys_write system call:
; - rax: system call number (sys_write)
; - rdi: file descriptor (stdout)
; - rsi: pointer to string
; - rdx: string length
mov rax, 1
mov rdi, 1
mov rsi, msg1
mov rdx, len1
syscall
; int3 should be here
mov rax, 1
mov rdi, 1
mov rsi, msg2
mov rdx, len2
syscall
; Execute sys_exit
mov rax, 60
mov rdi, 0
syscall
section .data
msg1 db 'Hello, ', 0xa
len1 equ $ - msg1
msg2 db 'world!', 0xa
len2 equ $ - msg2
这段代码编译如下：nasm -f elf64 hello.s && ld -s -o hello hello.o:
~$ objdump -d hello
hello: file format elf64-x86-64
Disassembly of section .text:
00000000004000b0 <.text>:
4000b0: 48 b8 01 00 00 00 00 movabs $0x1,%rax
4000b7: 00 00 00
4000ba: 48 bf 01 00 00 00 00 movabs $0x1,%rdi
4000c1: 00 00 00
4000c4: 48 be 1c 01 60 00 00 movabs $0x60011c,%rsi
4000cb: 00 00 00
4000ce: 48 ba 08 00 00 00 00 movabs $0x8,%rdx
4000d5: 00 00 00
4000d8: 0f 05 syscall
4000da: 48 b8 01 00 00 00 00 movabs $0x1,%rax
4000e1: 00 00 00
4000e4: 48 bf 01 00 00 00 00 movabs $0x1,%rdi
4000eb: 00 00 00
4000ee: 48 be 24 01 60 00 00 movabs $0x600124,%rsi
4000f5: 00 00 00
4000f8: 48 ba 07 00 00 00 00 movabs $0x7,%rdx
4000ff: 00 00 00
400102: 0f 05 syscall
400104: 48 b8 3c 00 00 00 00 movabs $0x3c,%rax
40010b: 00 00 00
40010e: 48 bf 00 00 00 00 00 movabs $0x0,%rdi
400115: 00 00 00
400118: 0f 05 syscall
之后，我尝试在 C 程序中设置断点，如文章中所述。
#include <stdio.h>
#include <stdarg.h>
#include <stdlib.h>
#include <signal.h>
#include <syscall.h>
#include <sys/ptrace.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/reg.h>
#include <sys/user.h>
#include <unistd.h>
#include <errno.h>
void procmsg(const char* format, ...)
{
va_list ap;
fprintf(stdout, "[%d] ", getpid());
va_start(ap, format);
vfprintf(stdout, format, ap);
va_end(ap);
}
void run_target(const char* programname)
{
procmsg("target started. will run '%s'\n", programname);
/* Allow tracing of this process */
if (ptrace(PTRACE_TRACEME, 0, 0, 0) < 0) {
perror("ptrace");
return;
}
/* Replace this process's image with the given program */
execl(programname, programname, (char *)NULL);
}
void run_debugger(pid_t child_pid)
{
int wait_status;
struct user_regs_struct regs;
procmsg("debugger started\n");
/* Wait for child to stop on its first instruction */
wait(&wait_status);
/* Obtain and show child's instruction pointer */
ptrace(PTRACE_GETREGS, child_pid, 0, ®s);
procmsg("Child started. RIP = 0x%08x\n", regs.rip);
unsigned addr = 0x004000da;
unsigned data = ptrace(PTRACE_PEEKTEXT, child_pid, (void*)addr, 0);
procmsg("Original data at 0x%08x: 0x%08x\n", addr, data);
/* Write the trap instruction 'int 3' into the address */
unsigned data_with_trap = (data & 0xFFFFFF00) | 0xCC;
ptrace(PTRACE_POKETEXT, child_pid, (void*)addr, (void*)data_with_trap);
/* See what's there again... */
unsigned readback_data = ptrace(PTRACE_PEEKTEXT, child_pid, (void*)addr, 0);
procmsg("After trap, data at 0x%08x: 0x%08x\n", addr, readback_data);
/* Let the child run to the breakpoint and wait for it to
** reach it
*/
ptrace(PTRACE_CONT, child_pid, 0, 0);
wait(&wait_status);
if (WIFSTOPPED(wait_status)) {
procmsg("Child got a signal: %s\n", strsignal(WSTOPSIG(wait_status)));
}
else {
perror("wait");
return;
}
/* See where the child is now */
ptrace(PTRACE_GETREGS, child_pid, 0, ®s);
procmsg("Child stopped at RIP = 0x%08x\n", regs.rip);
/* Remove the breakpoint by restoring the previous data
** at the target address, and unwind the EIP back by 1 to
** let the CPU execute the original instruction that was
** there.
*/
ptrace(PTRACE_POKETEXT, child_pid, (void*)addr, (void*)data);
regs.rip -= 1;
ptrace(PTRACE_SETREGS, child_pid, 0, ®s);
/* The child can continue running now */
ptrace(PTRACE_CONT, child_pid, 0, 0);
wait(&wait_status);
if (WIFEXITED(wait_status)) {
procmsg("Child exited\n");
}
else {
procmsg("Unexpected signal\n");
}
}
int main(int argc, char** argv)
{
pid_t child_pid;
if (argc < 2) {
fprintf(stderr, "Expected a program name as argument\n");
return -1;
}
child_pid = fork();
if (child_pid == 0)
run_target(argv[1]);
else if (child_pid > 0)
run_debugger(child_pid);
else {
perror("fork");
return -1;
}
return 0;
}
此代码也可以编译，但在执行期间会导致分段错误：
~$ ./ptrace_test_bp hello
[24100] debugger started
[24101] target started. will run 'hello'
[24100] Child started. RIP = 0x004000b0
[24100] Original data at 0x004000da: 0x0001b848
[24100] After trap, data at 0x004000da: 0x0001b8cc
Hello,
[1] 24100 segmentation fault (core dumped) ./ptrace_test_bp hello
我应该怎么做才能使其在 x64 上正常运行（在断点处停止并恢复）？
【问题讨论】：
标签： c linux debugging x86-64 ptrace