摘要
Gcov是gcc自带的代码覆盖率统计工具，配合lcov工具可以统计并生成代码覆盖率。Linux kernel将Gcov嵌入了原生的内核编译框架中，可以使用gcov统计内核代码覆盖情况。
内核编译
1.版本编译
1）打开kernel GCOV支持
我们需要打开如下的几个config项：
CONFIG_DEBUG_FS=y
CONFIG_GCOV_KERNEL=y
CONFIG_GCOV_FORMAT_AUTODETECT=y
CONFIG_GCOV_PROFILE_ALL=y
2）使用
make; make install等步骤替换系统内核，然后重启系统，进入新编译内核。
覆盖了统计
1.执行下面命令对覆盖率清零
# lcov -z
Auto-detecting gcov kernel support.
Found upstream gcov kernel support at /sys/kernel/debug/gcov
Resetting kernel execution counters
Done.
2.编译下面测试用例，并执行
# cat test.c
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
void main()
{
open("a", O_WRONLY|O_CREAT);
}
# ./test
3.下面命令统计覆盖率
# lcov -c -o kernel.info （统计内核下所有代码覆盖了）
# lcov -c -k fs -o fs.info（指定内核代码下fs文件夹代码覆盖率）
4.获取 HTML 输出
# genhtml fs.info -o fs_conv_result
fs_conv_result 指定生成的文件存放路径，然后文件夹拷贝出来可浏览器打开查看。
5.Linux下查看
# lcov -l fs.info
Reading tracefile fs.info
lcov: WARNING: negative counts found in tracefile fs.info
|Lines |Functions|Branches
Filename |Rate Num|Rate Num|Rate Num
================================================================================
[/home/cuibixuan/git/linux/]
arch/x86/include/asm/arch_hweight.h | 0.0% 2| - 0| - 0
arch/x86/include/asm/atomic.h |64.3% 14| - 0| - 0
arch/x86/include/asm/atomic64_64.h |92.3% 13| - 0| - 0
arch/x86/include/asm/barrier.h | 100% 1| - 0| - 0
arch/x86/include/asm/bitops.h |63.3% 30| - 0| - 0
arch/x86/include/asm/cpufeature.h | 0.0% 1| - 0| - 0
arch/x86/include/asm/current.h | 100% 1| - 0| - 0
arch/x86/include/asm/elf.h | 100% 7| - 0| - 0
arch/x86/include/asm/hugetlb.h | 0.0% 1| - 0| - 0
arch/x86/include/asm/io.h | 0.0% 1| - 0| - 0
arch/x86/include/asm/irqflags.h | 100% 5| - 0| - 0
arch/x86/include/asm/jump_label.h | 100% 1| - 0| - 0
arch/x86/include/asm/msr.h | 0.0% 2| - 0| - 0
arch/x86/include/asm/page.h | 0.0% 1| - 0| - 0
arch/x86/include/asm/page_64.h |66.7% 3| - 0| - 0
arch/x86/include/asm/pgtable.h | 0.0% 18| - 0| - 0
arch/x86/include/asm/pgtable_64.h | 0.0% 1| - 0| - 0
arch/x86/include/asm/pgtable_types.h | 0.0% 4| - 0| - 0
arch/x86/include/asm/pkeys.h | 0.0% 1| - 0| - 0
arch/x86/include/asm/preempt.h | 100% 1| - 0| - 0
arch/x86/include/asm/processor.h | 100% 2| - 0| - 0
arch/x86/include/asm/smap.h | 100% 2| - 0| - 0
arch/x86/include/asm/stacktrace.h | 0.0% 2| - 0| - 0
arch/x86/include/asm/uaccess.h |83.3% 6| - 0| - 0
arch/x86/include/asm/uaccess_64.h |37.5% 24| - 0| - 0
arch/x86/include/asm/word-at-a-time.h | 100% 5| - 0| - 0
fs/aio.c | 0.7% 591| 2.0% 50| - 0
fs/anon_inodes.c | 0.0% 42| 0.0% 5| - 0
fs/attr.c |57.1% 112|66.7% 6| - 0
fs/autofs/autofs_i.h | 0.0% 17| - 0| - 0
fs/autofs/dev-ioctl.c | 0.0% 212| 0.0% 25| - 0
fs/autofs/expire.c | 0.0% 193| 0.0% 13| - 0
fs/autofs/init.c | 0.0% 12| 0.0% 3| - 0
fs/autofs/inode.c | 0.0% 170| 0.0% 9| - 0
fs/autofs/root.c | 0.0% 277| 0.0% 21| - 0
fs/autofs/symlink.c | 0.0% 6| 0.0% 1| - 0
fs/autofs/waitq.c | 0.0% 215| 0.0% 8| - 0
fs/bad_inode.c | 3.4% 58| 4.0% 25| - 0
fs/binfmt_elf.c |42.2% 661|33.3% 24| - 0
fs/binfmt_script.c |83.7% 49|33.3% 3| - 0
fs/block_dev.c | 1.9% 748| 6.8% 73| - 0
fs/btrfs/acl.c | 0.0% 48| 0.0% 4| - 0
fs/btrfs/async-thread.c | 0.0% 133| 0.0% 34| - 0
fs/btrfs/backref.c | 0.0% 760| 0.0% 38| - 0
fs/btrfs/btrfs_inode.h | 0.0% 26| - 0| - 0
fs/btrfs/compression.c | 0.0% 493| 0.0% 27| - 0
fs/btrfs/ctree.c | 0.0% 2151| 0.0% 86| - 0
