GDB：如何将内存地址转换为 STL 对象

Question

I am analyzing a core dump by using GDB. I know about a memory address that it is pointing to "std::basic_fstream<wchar_t, std::char_traits<wchar_t> >".

How to cast raw memory address to this template object on GDB prompt?

I tried by below command:

(gdb) p *('std::basic_fstream<wchar_t, std::char_traits<wchar_t> >' *)0x7fae3800b280 No symbol "std::basic_fstream<wchar_t, std::char_traits<wchar_t> >" in current context.

(gdb) p *(std::basic_fstream<wchar_t, std::char_traits<wchar_t> > *)0x7fae3800b280 A syntax error in expression, near `)0x7fae3800b280'.

Answer 1

I tried by below command:

Wild guess: do you have set auto-solib-add off in your ~/.gdbinit ?

The following example works fine for me:

cat t.cc
#include <fstream>

int main(int argc, char *argv[])
{
  std::wfstream s("/dev/tty", s.out);
  for (int j = 0; j < argc; j++)
    s << j << " " << argv[j] << std::endl;
  return 0;
}

g++ -g t.cc && gdb -q ./a.out

(gdb) b 8
Breakpoint 1 at 0x1235: file t.cc, line 8.
(gdb) run foo
Starting program: /tmp/a.out foo
0 /tmp/a.out
1 foo

Breakpoint 1, main (argc=2, argv=0x7fffffffdc28) at t.cc:8
8         return 0;
(gdb) set print static off

(gdb) p s
$1 = {<std::basic_iostream<wchar_t, std::char_traits<wchar_t> >> = {<std::basic_istream<wchar_t, std::char_traits<wchar_t> >> = {<std::basic_ios<wchar_t, std::char_traits<wchar_t> >> = ...

(gdb) p &s
$2 = (std::wfstream *) 0x7fffffffd900

(gdb) p *('std::basic_fstream<wchar_t, std::char_traits<wchar_t> >' *)0x7fffffffd900
$3 = {<std::basic_iostream<wchar_t, std::char_traits<wchar_t> >> = {<std::basic_istream<wchar_t, std::char_traits<wchar_t> >> = {<std::basic_ios<wchar_t, std::char_traits<wchar_t> >> = {<std::ios_base> = ...

You should try to replicate above output.

If you can reproduce it, your tools are working as expected, and you need to concentrate on how you are analyzing the core dump.

If above example doesn't work as expected, you have some part of the toolchain which is misbehaving or misconfigured.

One way I was able to achieve No symbol result is by setting auto-solib-add off :

gdb -q ./a.out
Reading symbols from ./a.out...

(gdb) b 8
Breakpoint 1 at 0x1235: file t.cc, line 8.
(gdb) set auto-solib-add off
(gdb) run
Starting program: /tmp/a.out
0 /tmp/a.out

Breakpoint 1, main (argc=1, argv=0x7fffffffdc28) at t.cc:8
8         return 0;

(gdb) p &s
$1 = (std::wfstream *) 0x7fffffffd900

(gdb) p *('std::basic_fstream<wchar_t, std::char_traits<wchar_t> >' *) 0x7fffffffd900
No symbol "std::basic_fstream<wchar_t, std::char_traits<wchar_t> >" in current context.