gcov-dump原理分析_Linux平台代码覆盖率测试 dump

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gcov-dump原理分析_Linux平台代码覆盖率测试 时间：2011/7/12 8:18:44来源：本站原创作者：清晨我要评论(0)

第 12 页 dump_file 函数分析

2.2 dump_file 函数分析

gcov-dump 程序的主函数 main ，是靠调用 dump_file() 函数来完成文件内容的输出。该函数定义如下。其中的注释为笔者所加。

static void
dump_file ( const char * filename )
{
    unsigned tags [ 4 ];
    unsigned depth = 0 ;

    if ( ! gcov_open ( filename , 1 )) /* it will open .gcda/.gcno file, and save information into gcov_var */
    {
        fprintf ( stderr , "%s:cannot open/n" , filename );
        return ;
    }

    /* magic */
    {
        unsigned magic = gcov_read_unsigned ();
        unsigned version ;
        const char * type = NULL ;
        int endianness = 0 ;
        char m [ 4 ], v [ 4 ];

        /***** compare magic read just now with "gcda" or "gcno" to confirm file type */
        if (( endianness = gcov_magic ( magic , GCOV_DATA_MAGIC )))
            type = "data" ;
        else if (( endianness = gcov_magic ( magic , GCOV_NOTE_MAGIC )))
             type = "note" ;
        else
        {
            printf ( "%s:not a gcov file/n" , filename );
            gcov_close ();
            return ;
        }
        /***** read version, an unsigned word */
        version = gcov_read_unsigned ();

        /***** Convert a magic or version number to a 4 character string with ASCII */
        GCOV_UNSIGNED2STRING ( v , version );
        GCOV_UNSIGNED2STRING ( m , magic );
        printf ("%s:%s:magic `%.4s':version `%.4s'%s/n", filename , type ,
                m , v , endianness < 0 ? " (swapped endianness)" : "");
        if ( version != GCOV_VERSION )
        {
              char e [ 4 ];
             GCOV_UNSIGNED2STRING ( e , GCOV_VERSION );
             printf ( "%s:warning:current version is `%.4s'/n" , filename , e );
        }
    }

    /* stamp */
    {
        unsigned stamp = gcov_read_unsigned ();
        printf ( "%s:stamp %lu/n" , filename , ( unsigned long ) stamp );
    }

    while ( 1 )
    {
        gcov_position_t base , position = gcov_position ();
        unsigned tag , length ; tag_format_t const * format ; unsigned tag_depth ;
        int error ;
        unsigned mask ;

        /***** read a tag, for example, 0x01000000, 0x01a10000, 0xa1000000, etc */
        tag = gcov_read_unsigned ();
        if ( ! tag ) /***** tag=0x00000000, then, to the end of file, break *****/
            break ;

        /***** read its length tag */
        length = gcov_read_unsigned ();
        base = gcov_position ();

        /***** for example, tag=0x01000000, then, tag- 1=0xFFFFFF,
          * then, GCOV_TAG_MASK (tag)=0x1FFFFFF, then, mask = 0x1FFFFFF/ 2 = 0xFFFFFF
        */
        mask = GCOV_TAG_MASK ( tag ) >> 1 ;

        /****** validate the tag */
        for ( tag_depth = 4 ; mask ; mask >>= 8 )
        {
            if (( mask & 0xff ) != 0xff )
            {
                printf ( "%s:tag `%08x' is invalid/n" , filename , tag );
                break ;
            }
            tag_depth -- ;
        }

        /***** find the tag in tag_table, if found, then call its procedure */
        for ( format = tag_table ; format - >name ; format ++ )
            if ( format - >tag == tag )
                goto found ;
        format = & tag_table [ GCOV_TAG_IS_COUNTER ( tag ) ? 2 : 1 ];
found :
        ;
        if ( tag )
        {
            if ( depth && depth < tag_depth )
            {
                if ( ! GCOV_TAG_IS_SUBTAG ( tags [ depth - 1 ], tag ))
                printf ( "%s:tag `%08x' is incorrectly nested/n" ,
                filename , tag );
            }
            depth = tag_depth ;
            tags [ depth - 1 ] = tag ;
        }

        /***** print some spaces to represent the depth level */
        print_prefix ( filename , tag_depth , position );
        printf ( "%08x:%4u:%s" , tag , length , format - >name );
        /***** call the procedure of this tag stored in tag_table */
        if ( format - >proc )
             (*format- >proc) (filename, tag, length); // 此处调用相应的 tag 处理函数

        printf ( "/n" );
        if ( flag_dump_contents && format - >proc )
        {
            unsigned long actual_length = gcov_position () - base ;
            if ( actual_length > length )
                printf ( "%s:record size mismatch %lu bytes overread/n" ,
                    filename , actual_length - length );
            else if ( length > actual_length )
                printf ( "%s:record size mismatch %lu bytes unread/n" ,
                    filename , length - actual_length );
        }

        /***** base stands for the base position of a tag, then, synchronize the pointer */
        gcov_sync ( base , length );
        if (( error = gcov_is_error ()))
        {
            printf ( error < 0 ? "%s:counter overflow at %lu/n" :
                "%s:read error at %lu/n" , filename ,
                ( long unsigned ) gcov_position ());
            break ;
        }
    }
    gcov_close ();
}

dump_file 函数首先通过 gcov_open 打开 .gcda/.gcno 文件，将文件信息保存到全局变量 gcov_var( 稍后介绍该变量 ) ，接着读取文件头信息，包括 magic ， version ， stamp ，然后循环读取每个 tag ， length ，并通过函数指针处理该 tag ，直到文件结束 (0x00000000) 。下面介绍各种 tag 的 callback 。

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