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mock C++ function for unit test

byronhe

发布于 2021-06-25 02:49:58

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文章被收录于专栏：Tech ExplorerTech Explorer

在单元测试中，我们需要提供业务逻辑的mock版本，当业务逻辑实现为C++的virtual function时，这是很容易的，我们只需要写一个子类，实现virtual function就行了，Google 的 gmock就针对这种情况设计。

可是，如果遗留代码中有一般C函数，非virtual的类成员函数，模板函数，inline函数，如何提供mock版本呢？

下面的代码用一点trick实现了上述函数的运行时mock。

原理是，在运行时，修改目标函数的机器码，改为jmp到mock版本的函数中。

实现如下：

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#include <stdint.h> #include <iostream> #include <string> #include <unistd.h> #include <string.h> #include <sys/mman.h> #include "patch_elf.h" using namespace std; int print_op(void * addr,int leng){ unsigned char * op=(unsigned char *) addr; cout<<endl<<"addr:"<<addr<<" code:"<<endl; for(int i=0;i<leng;++i){ cout<<"0x"<<hex<<(unsigned int)op[i]<<" "; } cout<<endl; return 0; } int patch_func(void * original,void * mock){ /* cout<<endl<<"----------------------------------------------------------------------" <<endl<<__func__<<" ,i am going to patch "<<original<<" to "<<mock <<endl; */ //rax 用于保存函数调用的返回值，所以可以占用 //4010e1: b8 20 0c 40 00 mov $0x400c20,%eax //4010e6: ff e0 jmpq *%rax uint32_t addr=(uint32_t)(uint64_t)mock; const int code_len=7; char inject_code[code_len]={0xb8,0x00,0x00,0x00,0x00,0xff,0xe0}; memcpy(&inject_code[1],(char*)&addr,4); //print_op(inject_code,code_len); //接下来，把inject_code复制到original这个位置 //print_op(original,100); //首先，要改掉内存的权限，增加写权限 const size_t length = sysconf(_SC_PAGESIZE); void * code_addr= (void*) ( ( (long) original/length)*length ); int ret=mprotect(code_addr, length, PROT_READ | PROT_WRITE | PROT_EXEC); if ( 0!=ret ) { cerr<<"mprotect failed! ret="<<ret<<endl; } //修改代码 memcpy( original,inject_code,code_len); //再去掉写权限 ret=mprotect(code_addr, length, PROT_READ | PROT_EXEC); if ( 0!=ret ) { cerr<<"mprotect failed! ret="<<ret<<endl; } //print_op(original,100); //cout<<"----------------------------------------------------------------------" // <<endl<<endl; return 0; }

测试了

1.一般函数 2.inline函数 3.一般成员函数 4.模板函数

并在：32位，64位; -O2, -O0，参数下编译

除了 inline函数没办法，其它的都有效

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#pragma once #include <iostream> #include <cstdio> using namespace std; class ST1{ public: uint32_t a; uint64_t b; char c[200]; double d; ST1 * e; ST1():a(0),b(0),d(0),e(0){ c[0]=0; } //类的成员函数 int member_func(); int member_func_mock(); }; int member_func_extern(ST1 * st); //一般函数 int original_func(ST1 * para1,ST1 para2,void * para3); int mock_func(ST1 * para1,ST1 para2,void * para3); //int ref_func(ST1 * para1,ST1 para2,void * para3); class Base{ private: uint32_t b; ST1 st; public: uint32_t a; Base():b(0),a(0){} }; //inline 函数 inline int inline_func(int a,int b){ int c=a+b+ 0x1111 * a + b/0x1111; printf("%s %d\n",__func__,c); return c; } inline int inline_func_mock(int a,int b){ int c=a+b+100; printf("%s %d\n",__func__,c); return c; } //模板函数 template <typename T> uint32_t get_member_a(T & t){ cout<<__func__<<" a="<<t.a<<endl; return t.a; } template <typename T> uint32_t get_member_b(T & t){ cout<<__func__<<" b="<<t.b<<endl; return t.b; }

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#include <stdint.h> #include <iostream> #include <string> #include <unistd.h> #include "func.h" using namespace std; int original_func(ST1 * para1,ST1 para2,void * para3){ cout<<__func__<<"\tcalled! " <<" a+a "<<para1->a+para2.a <<" b+b "<<para1->b+para2.b <<" c+c "<<para1->c<<para2.c <<" d+d "<<para1->d+para2.d <<" e+e "<<para1->e<<para2.e <<para3 <<endl; return 0; } int mock_func(ST1 * para1,ST1 para2,void * para3){ cout<<__func__<<"\tcalled!" <<endl; return 0; } int ref_func(ST1 * para1,ST1 para2,void * para3){ return mock_func(para1,para2,para3); } int ST1::member_func(){ cout<<__func__<<" called! " <<" a="<< this->a <<" b="<< this->b <<" c="<< this->c <<" d="<< this->d <<endl; return 0; } int ST1::member_func_mock(){ cout<<__func__<<" called! i do nothing." <<endl; return 0; } int member_func_extern(ST1 * st){ cout<<__func__<<" called! i am not member function." <<endl; return 0; }

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#include <stdint.h> #include <iostream> #include <string> #include <unistd.h> #include <string.h> #include <sys/mman.h> #include "func.h" #include "patch_elf.h" using namespace std; int test(){ ST1 s1,s2; char str[]="hello"; s1.a=s1.b=s1.d=1; s1.e=NULL; s2.a=s2.b=s2.d=2; s1.e=NULL; cout<<"----------------------------------------------------------------------"<<endl; //mock original_func，替换成mock_func original_func(&s1,s2,&str[0]); patch_func((void*)&original_func, (void*)&mock_func); original_func(&s1,s2,&str[0]); cout<<"----------------------------------------------------------------------"<<endl; //mock inline 函数貌似不行 int a=s1.a, b=s1.b; inline_func(a,b); patch_func( (void*) &inline_func, (void*) &inline_func_mock); inline_func(a,b); cout<<"----------------------------------------------------------------------"<<endl; s1.member_func(); patch_func( (void*) &ST1::member_func, (void*) &ST1::member_func_mock); s1.member_func(); patch_func( (void*) &ST1::member_func, (void*) &member_func_extern); s1.member_func(); cout<<"----------------------------------------------------------------------"<<endl; get_member_a(s1); patch_func( (void*) & get_member_a<ST1> , (void*) & get_member_b<ST1>); get_member_a(s1); return 0; } int main(){ test(); return 0; }

可以参考