GCOV的使用-測試代碼覆寫率

1. gcov是什麼？

Gcov is GCC Coverage

是一個測試代碼覆寫率的工具

是一個指令行方式的控制台程式

伴随GCC釋出，配合GCC共同實作對C/C++檔案的語句覆寫和分支覆寫測試；

與程式概要分析工具(profiling tool，例如gprof)一起工作，可以估計程式中哪一段代碼最耗時；

注：程式概要分析工具是分析代碼性能的工具。

2. gcov能做什麼？

gcov可以統計

每一行代碼的執行頻率

實際上哪些代碼确實被執行了

每一段代碼(section code)的耗時(執行時間)

是以，gcov可以幫你優化代碼，當然這個優化動作還是應該有開發者完成。

3. 如何使用gcov？

#include <iostream>
using namespace std;
int main()
{
    int i,total;
    total = 0;
    for (i=0; i<10; i++)
        total += i;
    if (total != 45)
        cout << "Failure!" << endl;
    else
        cout << "Success!" << endl;
    return 0;
}

3.1 使用gcov的3個階段

(1) 編譯

$ g++ -fprofile-arcs -ftest-coverage -o main main.cpp

$   ls

-rwxrwxr-x. 1 heli heli 20281 Dec  7 11:54 main
-rw-rw-r--. 1 heli heli   217 Dec  7 10:57 main.cpp
-rw-rw-r--. 1 heli heli  6632 Dec  7 11:54 main.gcno

-fprofile-arcs -ftest-coverage告訴編譯器生成gcov需要的額外資訊，并在目标檔案中插入gcov需要的extra

profiling information。是以，該指令在生成可執行檔案test的同時生成mian.gcno檔案(gcov

note檔案)。

(2) 收集資訊

執行該程式，生成main.gcda檔案(gcov data檔案)。

(3) 報告

$ ./main 
Success!
$ ll
total 36
-rwxrwxr-x. 1 heli heli 20281 Dec  7 11:54 main
-rw-rw-r--. 1 heli heli   217 Dec  7 10:57 main.cpp
-rw-rw-r--. 1 heli heli   784 Dec  7 11:56 main.gcda
-rw-rw-r--. 1 heli heli  6632 Dec  7 11:54 main.gcno

$ gcov main.cpp 
File '/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/ios_base.h'
Lines executed:0.00% of 2
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/ios_base.h:creating 'ios_base.h.gcov'

File '/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/ostream'
Lines executed:0.00% of 11
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/ostream:creating 'ostream.gcov'

File '/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/basic_ios.h'
Lines executed:0.00% of 10
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/basic_ios.h:creating 'basic_ios.h.gcov'

File 'main.cpp'
Lines executed:88.89% of 9
main.cpp:creating 'main.cpp.gcov'

File '/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/iostream'
Lines executed:100.00% of 1
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/iostream:creating 'iostream.gcov'

File '/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/char_traits.h'
Lines executed:0.00% of 2
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/char_traits.h:creating 'char_traits.h.gcov'

File '/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/locale_facets.h'
Lines executed:0.00% of 5
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/locale_facets.h:creating 'locale_facets.h.gcov'

$ ll
total 300
-rw-rw-r--. 1 heli heli  22753 Dec  7 11:57 basic_ios.h.gcov
-rw-rw-r--. 1 heli heli  25834 Dec  7 11:57 char_traits.h.gcov
-rw-rw-r--. 1 heli heli  44130 Dec  7 11:57 ios_base.h.gcov
-rw-rw-r--. 1 heli heli   4084 Dec  7 11:57 iostream.gcov
-rw-rw-r--. 1 heli heli 132403 Dec  7 11:57 locale_facets.h.gcov
-rwxrwxr-x. 1 heli heli  20281 Dec  7 11:54 main
-rw-rw-r--. 1 heli heli    217 Dec  7 10:57 main.cpp
-rw-rw-r--. 1 heli heli    618 Dec  7 11:57 main.cpp.gcov
-rw-rw-r--. 1 heli heli    784 Dec  7 11:56 main.gcda
-rw-rw-r--. 1 heli heli   6632 Dec  7 11:54 main.gcno
-rw-rw-r--. 1 heli heli  27743 Dec  7 11:57 ostream.gcov

生成:

main.cpp.gcov

檔案，該檔案記錄了每行代碼被執行的次數。

main.cpp.gcov檔案内容如下:

-:    0:Source:main.cpp
        -:    0:Graph:main.gcno
        -:    0:Data:main.gcda
        -:    0:Runs:1
        -:    0:Programs:1
        -:    1:#include <iostream>
        -:    2:using namespace std;
        1:    3:int main()
        -:    4:{
        -:    5:    int i,total;
        1:    6:    total = 0;
        -:    7:
       11:    8:    for (i=0; i<10; i++)
       10:    9:        total += i;
        -:   10:
        1:   11:    if (total != 45)
    #####:   12:        cout << "Failure!" << endl;
        -:   13:    else
        1:   14:        cout << "Success!" << endl;
        1:   15:    return 0;
        3:   16:}

3.2 gcov的選項

gcov的選項不多，也好了解，此處選3個典型的選項并結合例子加以說明。

(1) -a, --all-blocks

在.gcov檔案中輸出每個基本快(basic block)的執行次數。如果沒有-a選項，則輸出'main'函數這個block的執行次數，如上所示。使用該選項可以

Write individual execution counts for every basic block. Normally gcov outputs execution counts only for the main blocks of a line. With this option you can determine if blocks within

a single line are not being executed.

# gcov -a main.cpp

$ gcov -a main.cpp
File '/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/ios_base.h'
Lines executed:0.00% of 2
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/ios_base.h:creating 'ios_base.h.gcov'

File '/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/ostream'
Lines executed:0.00% of 11
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/ostream:creating 'ostream.gcov'

File '/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/basic_ios.h'
Lines executed:0.00% of 10
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/basic_ios.h:creating 'basic_ios.h.gcov'

File 'main.cpp'
Lines executed:88.89% of 9
main.cpp:creating 'main.cpp.gcov'

File '/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/iostream'
Lines executed:100.00% of 1
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/iostream:creating 'iostream.gcov'

File '/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/char_traits.h'
Lines executed:0.00% of 2
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/char_traits.h:creating 'char_traits.h.gcov'

File '/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/locale_facets.h'
Lines executed:0.00% of 5
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/locale_facets.h:creating 'locale_facets.h.gcov'

main.cpp.gcov檔案内容。

-:    0:Source:main.cpp
        -:    0:Graph:main.gcno
        -:    0:Data:main.gcda
        -:    0:Runs:1
        -:    0:Programs:1
        -:    1:#include <iostream>
        -:    2:using namespace std;
        1:    3:int main()
        -:    4:{
        -:    5:    int i,total;
        1:    6:    total = 0;
        -:    7:
       11:    8:    for (i=0; i<10; i++)
        1:    8-block  0
       10:    8-block  1
       11:    8-block  2
       10:    9:        total += i;
        -:   10:
        1:   11:    if (total != 45)
        1:   11-block  0
    #####:   12:        cout << "Failure!" << endl;
    $$$$$:   12-block  0
        -:   13:    else
        1:   14:        cout << "Success!" << endl;
        1:   14-block  0
        1:   15:    return 0;
        1:   15-block  0
        3:   16:}
        1:   16-block  0
        1:   16-block  1
        1:   16-block  2
        1:   16-block  3

(2) -b, --branch-probabilities

在.gcov檔案中輸出每個分支的執行頻率，并有分支統計資訊。

# gcov -b main.cpp

(3) -c, --branch-counts

在.gcov檔案中輸出每個分支的執行次數。

# gcov -c main.cpp

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