我正在尝试关注this guide以设置断点来获得相同的结果，唯一的区别是我在x64系统上。所以，我有“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
此代码编译如下：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，在C程序中，我试图设置一个断点，正如文章中所描述的那样。
#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;
}
此代码也会编译，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它在x64上正常运行（在断点处停止并恢复）？
答案 0 :(得分：3)
您的C代码在strsignal中是分段的，因为您忘记了#include <string.h>。
准确地说，它是segfaulting，因为没有原型，strsignal的返回值被假定为int（32位），而实际上它是64位的指针。
答案 1 :(得分：1)
@Enchantner，谢谢您的提问。我最近遇到类似的问题。这启发了我很多。根据@Jester修复错误后，仍然存在段错误。所以我花了一些时间来研究它。最后，我解决了。
在x86-64 Linux上，peek / poke的ptrace字长为64位而不是32位。但是代码使用的是unsigned（32位），它将在ptrace(2)调用中转换为64位长型。
例如，0xaabbccdd的POKETEXT实际上会将0x00000000aabbccdd写到内存中，假设调用者恰好将其扩展了零。必然会破坏内存。
因此可以将类型更改为long，这是x86-64 System V ABI中的64位。
#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>
#include <string.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);
long addr = 0x004000cb;//0x004000da;
long 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 */
long data_with_trap = (data & 0xFFFFFFFFFFFFFF00) | 0xCC;
ptrace(PTRACE_POKETEXT, child_pid, (void*)addr, (void*)data_with_trap);
/* See what's there again... */
long 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);
/* See what's there again... */
readback_data = ptrace(PTRACE_PEEKTEXT, child_pid, (void*)addr, 0);
procmsg("After restore, data at 0x%08x: 0x%08x\n", addr, readback_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 if(WIFSIGNALED(wait_status)) {
procmsg("signal !!!\n");
}
else {
procmsg("Unexpected signal. %s \n", strsignal(WSTOPSIG(wait_status)));
}
}
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;
}
此外，您必须根据编译的目标文件来修改long addr = 0x004000cb;//0x004000da;。您会发现我的Ubuntu系统中的指南有所不同。
________________除法器______________________________
首先，这是我的推断，确实表明它可以解决问题。但我想测试更多以证实结论。这是我的测试代码。
objdump -d hello2输出
hello2: file format elf64-x86-64
Disassembly of section .text:
00000000004000b0 <.text>:
4000b0: b8 01 00 00 00 mov $0x1,%eax
4000b5: bf 01 00 00 00 mov $0x1,%edi
4000ba: 48 be f4 00 60 00 00 movabs $0x6000f4,%rsi
4000c1: 00 00 00
4000c4: ba 08 00 00 00 mov $0x8,%edx
4000c9: 0f 05 syscall
4000cb: b8 01 00 00 00 mov $0x1,%eax
4000d0: bf 01 00 00 00 mov $0x1,%edi
4000d5: 48 be fc 00 60 00 00 movabs $0x6000fc,%rsi
4000dc: 00 00 00
4000df: ba 07 00 00 00 mov $0x7,%edx
4000e4: 0f 05 syscall
4000e6: b8 3c 00 00 00 mov $0x3c,%eax
4000eb: bf 00 00 00 00 mov $0x0,%edi
4000f0: 0f 05 syscall
debugger.c内容
#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>
#include <string.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%016x\n", regs.rip);
long addr = 0x004000cb;//0x004000da;
unsigned data = ptrace(PTRACE_PEEKTEXT, child_pid, (void*)addr, 0);
procmsg("Original data at 0x%016x: 0x%016x\n", addr, data);
//test
unsigned data_u = data;
procmsg("test data_u: 0x%08x\n", data_u);
/* Write the trap instruction 'int 3' into the address */
long data_with_trap = (data & 0xFFFFFFFFFFFFFF00) | 0xCC;
ptrace(PTRACE_POKETEXT, child_pid, (void*)addr, (void*)data_with_trap);
/* See what's there again... */
long readback_data = ptrace(PTRACE_PEEKTEXT, child_pid, (void*)addr, 0);
procmsg("After trap,set breakpoint, data at 0x%016x: 0x%016x\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 to breakpoint
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%016x\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.
*/
int result = ptrace(PTRACE_POKETEXT, child_pid, (void*)addr, (void*)data);
procmsg("poketext origin back result %d\n", result);
/* See what's there again... */
readback_data = ptrace(PTRACE_PEEKTEXT, child_pid, (void*)addr, 0);
procmsg("After restore, data at 0x%llx: 0x%llx\n", addr, readback_data);
int offset = 0;
for(offset = 1; offset < 25; offset++) {
readback_data = ptrace(PTRACE_PEEKTEXT, child_pid, (void*)(addr+offset), 0);
procmsg("After restore, data at 0x%llx: 0x%llx\n", addr+offset, readback_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 if(WIFSIGNALED(wait_status)) {
procmsg("signal !!!\n");
}
else {
procmsg("Unexpected signal. %s \n", strsignal(WSTOPSIG(wait_status)));
}
}
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;
}
./debugger.o hello2输出
[20832] debugger started
[20833] target started. will run 'hello2'
[20832] Child started. RIP = 0x00000000004000b0
[20832] Original data at 0x00000000004000cb: 0x00000000000001b8
[20832] test data_u: 0x000001b8
[20832] After trap,set breakpoint, data at 0x00000000004000cb: 0x00000000000001cc
Hello,
[20832] Child got a signal: Trace/breakpoint trap
[20832] Child stopped at RIP = 0x00000000004000cc
[20832] poketext origin back result 0
[20832] After restore, data at 0x4000cb: 0x1b8
[20832] After restore, data at 0x4000cc: 0x1
[20832] After restore, data at 0x4000cd: 0x0
[20832] After restore, data at 0x4000ce: 0x4800000000000000
[20832] After restore, data at 0x4000cf: 0xbe48000000000000
[20832] After restore, data at 0x4000d0: 0xfcbe480000000000
[20832] After restore, data at 0x4000d1: 0xfcbe4800000000
[20832] After restore, data at 0x4000d2: 0x6000fcbe48000000
[20832] After restore, data at 0x4000d3: 0x6000fcbe480000
[20832] After restore, data at 0x4000d4: 0x6000fcbe4800
[20832] After restore, data at 0x4000d5: 0x6000fcbe48
[20832] After restore, data at 0x4000d6: 0x6000fcbe
[20832] After restore, data at 0x4000d7: 0x6000fc
[20832] After restore, data at 0x4000d8: 0xba00000000006000
[20832] After restore, data at 0x4000d9: 0x7ba000000000060
[20832] After restore, data at 0x4000da: 0x7ba0000000000
[20832] After restore, data at 0x4000db: 0x7ba00000000
[20832] After restore, data at 0x4000dc: 0x7ba000000
[20832] After restore, data at 0x4000dd: 0xf00000007ba0000
[20832] After restore, data at 0x4000de: 0x50f00000007ba00
[20832] After restore, data at 0x4000df: 0xb8050f00000007ba
[20832] After restore, data at 0x4000e0: 0x3cb8050f00000007
[20832] After restore, data at 0x4000e1: 0x3cb8050f000000
[20832] After restore, data at 0x4000e2: 0x3cb8050f0000
[20832] After restore, data at 0x4000e3: 0x3cb8050f00
[20832] Unexpected signal. Segmentation fault
很显然，我要花很长时间才能取消签名并写回并循环打印。
......
unsigned data = ptrace(PTRACE_PEEKTEXT, child_pid, (void*)addr, 0);
procmsg("After restore, data at 0x%llx: 0x%llx\n", addr, readback_data);
......
int offset = 0;
for(offset = 1; offset < 25; offset++) {
readback_data = ptrace(PTRACE_PEEKTEXT, child_pid, (void*)(addr+offset), 0);
procmsg("After restore, data at 0x%llx: 0x%llx\n", addr+offset, readback_data);
}
.....
最后，输出，
[20832] After restore, data at 0x4000d0: 0xfcbe480000000000，
显示内存中的指令
4000d0: bf 01 00 00 00 mov $0x1,%edi
写入零。这将导致Segmentation fault达到预期。
我现在对答案感到满意。 ~~