在Linux中访问另一个进程虚拟内存（调试） [英] Accessing another process virtual memory in Linux (debugging)

问题描述

gdb如何在Linux上访问另一个进程虚拟内存？这一切是通过/ proc完成的吗？

解决方案

gdb如何在Linux上访问另一个进程虚拟内存？这一切是通过/ proc完成的吗？

用于阅读内存的Linux

：

1）如果要读取的字节数小于 3 * sizeof（long）或文件系统 / proc 不可用或从 / proc / PID / mem 读取失败，则 ptrace 与 PTRACE_PEEKTEXT 来读取数据。

以下是函数 linux_proc_xfer_partial（）中的这些条件：

  / *不要打扰一个字。 * / 
 if（len <3 * sizeof（long））
 return 0; 
 
 / *我们可以保持这个文件打开并缓存它 - 可能是每
线程一个。这需要一些杂耍，但速度更快。 * / 
 xsnprintf（文件名，sizeof文件名，/ proc /％d / mem，
 ptid_get_pid（inferior_ptid））; 
 fd = gdb_open_cloexec（filename，O_RDONLY | O_LARGEFILE，0）; 
 if（fd == -1）
 return 0; 
  

<2>如果要读取的字节数大于或等于3 * sizeof（long）和 / proc 可用，然后 pread64 或（ lseek（）并使用 read（）：

  static LONGEST 
 linux_proc_xfer_partial（struct target_ops * ops，enum target_object object，
 const char * annex，gdb_byte * readbuf，
 const gdb_byte * writebuf，
 ULONGEST offset，LONGEST len）
 {
 ..... 
 $ b $ *如果pread64可用，则使用它。如果内核
支持它（只有一个系统调用），则速度更快，即使在64位安全
 32位平台（例如，SPARC调试SPARC64 
应用程序）* / 
 #ifdef HAVE_PREAD64 
 if（pread64（fd，readbuf，len，offset）！= len）
 #else 
 if（lseek（fd，offset，SEEK_SET）== -1 || read（fd，readbuf，len）！= len）
 #endif 
 ret = 0; 
 else 
 ret = len ; 
 
 close（fd）; 
 return ret; 
 
  

在用于写入内存的Linux上：

>

<1> ptrace with PTRACE_POKETEXT 或使用PTRACE_POKEDATA 。

---

至于第二个问题：

在哪里可以找到关于......设置硬件观察点的信息

gdb，内部Watchpoint：s http://sourceware.org/gdb/wiki/Internals%20Watchpoints

参考：

• http://linux.die.net/man/2/ptrace


• http://www.alexonlinux.com/how-debugger-works

How does gdb access another process virtual memory on Linux? Is it all done via /proc?

解决方案

How does gdb access another process virtual memory on Linux? Is it all done via /proc?

On Linux for reading memory:

1) If the number of bytes to read is fewer than 3 * sizeof (long) or the filesystem /proc is unavailable or reading from /proc/PID/mem is unsuccessful then ptrace is used with PTRACE_PEEKTEXT to read data.

These are these conditions in the function linux_proc_xfer_partial():

  /* Don't bother for one word.  */
  if (len < 3 * sizeof (long))
    return 0;

  /* We could keep this file open and cache it - possibly one per
     thread.  That requires some juggling, but is even faster.  */
  xsnprintf (filename, sizeof filename, "/proc/%d/mem",
         ptid_get_pid (inferior_ptid));
  fd = gdb_open_cloexec (filename, O_RDONLY | O_LARGEFILE, 0);
  if (fd == -1)
    return 0;

2) If the number of bytes to read is greater or equal to 3 * sizeof (long) and /proc is available then pread64 or (lseek() and read() are used:

static LONGEST
linux_proc_xfer_partial (struct target_ops *ops, enum target_object object,
             const char *annex, gdb_byte *readbuf,
             const gdb_byte *writebuf,
             ULONGEST offset, LONGEST len)
{
  .....

  /* If pread64 is available, use it.  It's faster if the kernel
     supports it (only one syscall), and it's 64-bit safe even on
     32-bit platforms (for instance, SPARC debugging a SPARC64
     application).  */
#ifdef HAVE_PREAD64
  if (pread64 (fd, readbuf, len, offset) != len)
#else
  if (lseek (fd, offset, SEEK_SET) == -1 || read (fd, readbuf, len) != len)
#endif
    ret = 0;
  else
    ret = len;

  close (fd);
  return ret;
}

On Linux for writing memory:

1) ptrace with PTRACE_POKETEXT or PTRACE_POKEDATA is used.

---

As for your second question:

where can I find information about ... setting hardware watchpoints

gdb, Internals Watchpoint:s http://sourceware.org/gdb/wiki/Internals%20Watchpoints

Reference:

• http://linux.die.net/man/2/ptrace
• http://www.alexonlinux.com/how-debugger-works

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