LCOV在函数末尾分支

Question

这个函数末尾的分支是什么.我怎么能掩盖他们？

Answer 1

您正在观察gcc生成的代码,用于销毁静态存储持续时间(全局)变量.

您的报道显示该函数foo已输入三次,但是示波器末尾附近的计数器显示代码已执行八次,包括您查询的分支.

现在你必须考虑编译器将头文件放在转换单元中,并且gcov没有完全看到你的代码,而是作为汇编指令的控制流图,其中分支作为图的边缘.

因此,foolcov html输出中的" 范围结束"实际上并不是foo方法范围的结束,而是foo整个翻译单元中包含的所有内容,包括销毁在头文件中声明的全局变量.

标题本身没有包含在问题中,但即使__static_initialization_and_destruction是gcc生成的最基本的程序集也包含了许多分支.

请注意,您可能已包含全局变量,或者您可能没有 - gcc仍可能为每个翻译单元生成此代码.

看看gcov的底层输出:

function _Z3fooi called 1 returned 100% blocks executed 50%
        1:    4:int foo(int x) {
        1:    5:    if (x==1) {
branch  0 taken 0% (fallthrough)
branch  1 taken 100%
    #####:    6:        std::cout << "foo" << std::endl;
call    0 never executed
call    1 never executed
    #####:    7:        return 0;
        -:    8:    }
        1:    9:    return 1;
function _GLOBAL__sub_D__Z3fooi called 1 returned 100% blocks executed 100%
function _GLOBAL__sub_I__Z3fooi called 1 returned 100% blocks executed 100%
function _Z41__static_initialization_and_destruction_0ii called 2 returned 100% blocks executed 100%
        6:   10:}
call    0 returned 100%
call    1 returned 100%
branch  2 taken 50% (fallthrough)
branch  3 taken 50%
branch  4 taken 100% (fallthrough)
branch  5 taken 0%
        -:   11:

并查看生成的程序集,修剪以澄清要点:

        ...
        ret
        .seh_endproc
        .def    _Z41__static_initialization_and_destruction_0ii;        .scl    3;      .type   32;     .endef
        .seh_proc       _Z41__static_initialization_and_destruction_0ii
_Z41__static_initialization_and_destruction_0ii:
.LFB978:
        ...
        mov     QWORD PTR __gcov0._Z41__static_initialization_and_destruction_0ii[rip], rax
        cmp     DWORD PTR 16[rbp], 1
        jne     .L5                                 <-- BRANCH
        mov     rax, QWORD PTR __gcov0._Z41__static_initialization_and_destruction_0ii[rip+8]
        add     rax, 1
        mov     QWORD PTR __gcov0._Z41__static_initialization_and_destruction_0ii[rip+8], rax
        cmp     DWORD PTR 24[rbp], 65535
        jne     .L5                                 <-- BRANCH
        ...
.L5:
        cmp     DWORD PTR 16[rbp], 0
        je      .L6                                 <-- BRANCH