X64调试模式下返回STL容器的函数调试异常咨询

在X64架构Debug模式调试应用程序时，返回std::string、std::stack、std::vector这类非平凡类型的函数（如fooNoOk、barNook、bar2NoOk）会出现异常调试行为：调试器进入函数后会先跳转到return语句，再执行函数内代码，最后再次跳转至return语句。反汇编显示这类函数的return语句对应代码被生成两次；而返回int类型的foOk函数调试行为完全正常。

测试代码 #

#include <stack>
#include <vector>
#include <string>

std::stack<std::string> fooNoOk()
{
    std::stack<std::string> s;
    int r = 0;
    return s;
}

std::vector<int> barNook()
{
    std::vector<int> s;
    int r = 0;
    return s;
}

std::string bar2NoOk()
{
    std::string s;
    int r = 0;
    return s;
}

int foOk()
{
    int s{};
    int r = 0;
    return s;
}

int main()
{
    fooNoOk();
    barNook();
    bar2NoOk();
    foOk();
}

异常函数反汇编示例（fooNoOk） #

std::stack<std::string> fooNoOk()
{
00007FF63B544D30  mov         qword ptr [rsp+8],rcx  
00007FF63B544D35  push        rbp  
00007FF63B544D36  push        rdi  
00007FF63B544D37  sub         rsp,188h  
00007FF63B544D3E  lea         rbp,[rsp+20h]  
00007FF63B544D43  lea         rdi,[rsp+20h]  
00007FF63B544D48  mov         ecx,2Ah  
00007FF63B544D4D  mov         eax,0CCCCCCCCh  
00007FF63B544D52  rep stos    dword ptr [rdi]  
00007FF63B544D54  mov         rcx,qword ptr [rsp+1A8h]  
00007FF63B544D5C  mov         dword ptr [rbp+144h],0  
00007FF63B544D66  lea         rcx,[__F9076511_TestReturn@cpp (07FF63B55906Ah)]  
00007FF63B544D6D  call        __CheckForDebuggerJustMyCode (07FF63B54161Dh)  
    std::stack<std::string> s;
00007FF63B544D72  mov         edx,28h  
00007FF63B544D77  mov         rcx,qword ptr [rbp+180h]  
00007FF63B544D7E  call        std::stack<std::basic_string<char,std::char_traits<char>,std::allocator<char> >,std::deque<std::basic_string<char,std::char_traits<char>,std::allocator<char> >,std::allocator<std::basic_string<char,std::char_traits<char>,std::allocator<char> > > > >::__autoclassinit2 (07FF63B541280h)  
00007FF63B544D83  mov         rcx,qword ptr [rbp+180h]  
00007FF63B544D8A  call        std::stack<std::basic_string<char,std::char_traits<char>,std::allocator<char> >,std::deque<std::basic_string<char,std::char_traits<char>,std::allocator<char> >,std::allocator<std::basic_string<char,std::char_traits<char>,std::allocator<char> > > > >::stack<std::basic_string<char,std::char_traits<char>,std::allocator<char> >,std::deque<std::basic_string<char,std::char_traits<char>,std::allocator<char> >,std::allocator<std::basic_string<char,std::char_traits<char>,std::allocator<char> > > > > (07FF63B541532h)  
00007FF63B544D8F  mov         qword ptr [rbp+158h],rax  
    return s;
00007FF63B544D96  mov         eax,dword ptr [rbp+144h]  
00007FF63B544D9C  or          eax,1  
00007FF63B544D9F  mov         dword ptr [rbp+144h],eax  
    int r = 0;
00007FF63B544DA5  mov         dword ptr [r],0  
    return s;
00007FF63B544DAC  mov         rax,qword ptr [rbp+180h]  
}

正常函数反汇编示例（foOk） #

int foOk()
{
00007FF63B545500  push        rbp  
00007FF63B545502  push        rdi  
00007FF63B545503  sub         rsp,128h  
00007FF63B54550A  lea         rbp,[rsp+20h]  
00007FF63B54550F  lea         rcx,[__F9076511_TestReturn@cpp (07FF63B55906Ah)]  
00007FF63B545516  call        __CheckForDebuggerJustMyCode (07FF63B54161Dh)  
    int s{};
00007FF63B54551B  mov         dword ptr [s],0  
    int r = 0;
00007FF63B545522  mov         dword ptr [r],0  
    return s;
00007FF63B545529  mov         eax,dword ptr [s]  
}

问题原因 #

这是MSVC Debug模式下的返回值优化与调试信息错位导致的：

• Debug模式为了支持编辑并继续（Edit and Continue）功能，对返回非平凡类型（需要调用构造/析构函数）的函数，会生成额外的代码路径。第一次return对应的是编译器插入的临时对象初始化标记代码，用于处理返回值的构造逻辑；
• 第二次return才是执行完用户代码后的真正返回操作。调试器的源代码映射因为额外生成的代码出现错位，导致视觉上出现先跳转到return再执行函数体的异常现象；
• 返回int这类平凡类型的函数不需要复杂的返回值构造逻辑，编译器不会生成额外代码路径，因此调试行为完全正常。

内容的提问来源于stack exchange，提问作者amplifier