显示C++ vtable以及相应的内容

例子

#include <iostream>

    struct Base {
      virtual void f(){
        std::cout << "base\n";
      }
    };

    struct Derived : Base {
      void f() override // 'override' is optional
      {
        std::cout << "derived\n";
      }
    };

    int main() {
      Base b;
      Derived d;

      // virtual function call through reference
      Base& br = b; // the type of br is Base&
      Base& dr = d; // the type of dr is Base& as well
    }

技巧

为了观察一个对象的虚表和相应虚表的内容，可以在启动gdb后设置如下命令 set print asm-demangle on set print demangle on 已下面程序为例子

 (gdb) l
    int main() {
    Base b;
    Derived d;

    // virtual function call through reference
    Base& br = b; // the type of br is Base&
    Base& dr = d; // the type of dr is Base& as well
(gdb) n
    The program is not being run.
(gdb) r
    Starting program: /home/qinliansong/pblearn/main
    [Thread debugging using libthread_db enabled]
    Using host libthread_db library "/lib64/libthread_db.so.1".

Breakpoint 1, main () at main.cc:21
    Base b;
Missing separate debuginfos, use: debuginfo-install libgcc-4.8.5-39.el7.x86_64 libstdc++-4.8.5-39.el7.x86_64
(gdb) n
    Derived d;
(gdb) n
    Base& br = b; // the type of br is Base&

此时设置如下两个命令，几个命令，更友好的观察vtbl

set print vtbl on set print object on set print pretty on

(gdb) set print vtbl on
(gdb) p d
$1 = {<Base> = {_vptr.Base = 0x4009c0 <vtable for Derived+16>}, <No data fields>}
(gdb) set print object on
(gdb) set print pretty on
(gdb) p d
$2 = (Derived) {
      <Base> = {
        _vptr.Base = 0x4009c0 <vtable for Derived+16>
  }, <No data fields>}

通过info vtbl [expr]观察对象的虚函数

(gdb) info vtbl d
    vtable for 'Derived' @ 0x4009c0 (subobject @ 0x7fffffffde00):
    [0]: 0x4008f2 <Derived::f()>

(gdb) set print demangle on
(gdb) set print asm-demangle on
(gdb) x/28x 0x4009c0
    0x4009c0 <vtable for Derived+16>:    0x004008f2    0x00000000    0x00000000    0x00000000
    0x4009d0 <vtable for Base+8>:    0x00400a08    0x00000000    0x004008d4    0x00000000
    0x4009e0 <typeinfo for Derived>:    0x00600d90    0x00000000    0x004009f8    0x00000000
    0x4009f0 <typeinfo for Derived+16>:    0x00400a08    0x00000000    0x72654437    0x64657669
    0x400a00 <typeinfo name for Derived+8>:    0x00000000    0x00000000    0x00600d30    0x00000000
    0x400a10 <typeinfo for Base+8>:    0x00400a18    0x00000000    0x73614234    0x00000065
    0x400a20:    0x3b031b01    0x00000054    0x00000009    0xfffffc80


(gdb) info variables vtable for Derived
    All variables matching regular expression "vtable for Derived":

    Non-debugging symbols:
    0x00000000004009b0  vtable for Derived
(gdb) x /4a 0x00000000004009b0
    0x4009b0 <vtable for Derived>:    0x0    0x4009e0 <typeinfo for Derived>
    0x4009c0 <vtable for Derived+16>:    0x4008f2 <Derived::f()>    0x0
(gdb) x /10a 0x4009c0
    0x4009c0 <vtable for Derived+16>:    0x4008f2 <Derived::f()>    0x0
    0x4009d0 <vtable for Base+8>:    0x400a08 <typeinfo for Base>    0x4008d4 <Base::f()>
    0x4009e0 <typeinfo for Derived>:    0x600d90 <vtable for __cxxabiv1::__si_class_type_info@@CXXABI_1.3+16>    0x4009f8 <typeinfo name for Derived>
    0x4009f0 <typeinfo for Derived+16>:    0x400a08 <typeinfo for Base>    0x6465766972654437
    0x400a00 <typeinfo name for Derived+8>:    0x0    0x600d30 <vtable for __cxxabiv1::__class_type_info@@CXXABI_1.3+16>

参考

gdb手册 vtable-part1

贡献者

qls152