linux内核默认会包含git的commit ID。
而linux的内核在insmod模块时，会对模块和内核本身的版本做严格的校验。在开发产品时，改动内核后，由于commit ID变更，会导致linux内核变更，之前已编译发布的模块与升级后的linux版本不一致，必须重新编译，非常麻烦。
为了解决这个问题，很多开发者通过配置make menuconfig，去掉CONFIG_LOCALVERSION_AUTO选项，从而不再包含git commit ID。
关于linux包含git commit的实现原理，可以参考博文：
转： linux内核版本本地版本号的检查——setlocalversion
http://www.cnblogs.com/liuwanpeng/p/6148572.html
但是git的commit ID对于版本追溯又很有帮助，能够帮助我们追溯到特定的内核版本，本文通过以下方法，把git
commit ID包含到内核中，但是不属于内核版本的一部分，从而解决上述问题。
1.make menuconfig，去掉CONFIG_LOCALVERSION_AUTO选项，不自动包含git commit ID
2. 修改 /scripts/setlocalverison脚本，把git commit ID导出到一个单独的文件，命名为git_ver.h
#!/bin/sh # # This scripts adds local version information from the version # control systems git, mercurial (hg) and subversion (svn). # # If something goes wrong, send a mail the kernel build mailinglist # (see MAINTAINERS) and CC Nico Schottelius # <nico-linuxsetlocalversion -at- schottelius.org>. # # usage() { echo "Usage: $0 [--save-scmversion] [srctree]" >&2 exit 1 } scm_only=false srctree=. if test "$1" = "--save-scmversion"; then scm_only=true shift fi if test $# -gt 0; then srctree=$1 shift fi if test $# -gt 0 -o ! -d "$srctree"; then usage fi scm_version() { local short short=false cd "$srctree" if test -e .scmversion; then cat .scmversion return fi if test "$1" = "--short"; then short=true fi # Check for git and a git repo. if test -z "$(git rev-parse --show-cdup 2>/dev/null)" && head=`git rev-parse --verify --short HEAD 2>/dev/null`; then # If we are at a tagged commit (like "v2.6.30-rc6"), we ignore # it, because this version is defined in the top level Makefile. if [ -z "`git describe --exact-match 2>/dev/null`" ]; then # If only the short version is requested, don't bother # running further git commands if $short; then #echo "+" // modify by *，不要+号了，没啥意义 return fi # If we are past a tagged commit (like # "v2.6.30-rc5-302-g72357d5"), we pretty print it. if atag="`git describe 2>/dev/null`"; then echo "$atag" | awk -F- '{printf("-d-%s", $(NF-1),$(NF))}' # If we don't have a tag at all we print -g{commitish}. else #printf '%s%s' -g $head // modify by * printf '%s%s' $head fi fi # Is this git on svn? if git config --get svn-remote.svn.url >/dev/null; then printf -- '-svn%s' "`git svn find-rev $head`" fi # Check for uncommitted changes if git diff-index --name-only HEAD | grep -qv "^scripts/package"; then printf '%s' -dirty fi # All done with git return fi # Check for mercurial and a mercurial repo. if test -d .hg && hgid=`hg id 2>/dev/null`; then # Do we have an tagged version? If so, latesttagdistance == 1 if [ "`hg log -r . --template '{latesttagdistance}'`" == "1" ]; then id=`hg log -r . --template '{latesttag}'` printf '%s%s' -hg "$id" else tag=`printf '%s' "$hgid" | cut -d' ' -f2` if [ -z "$tag" -o "$tag" = tip ]; then id=`printf '%s' "$hgid" | sed 's/[+ ].*//'` printf '%s%s' -hg "$id" fi fi # Are there uncommitted changes? # These are represented by + after the changeset id. case "$hgid" in *+|*+\ *) printf '%s' -dirty ;; esac # All done with mercurial return fi # Check for svn and a svn repo. if rev=`LANG= LC_ALL= LC_MESSAGES=C svn info 2>/dev/null | grep '^Last Changed Rev'`; then rev=`echo $rev | awk '{print $NF}'` printf -- '-svn%s' "$rev" # All done with svn return fi } collect_files() { local file res for file; do case "$file" in *\~*) continue ;; esac if test -e "$file"; then res="$res$(cat "$file")" fi done echo "$res" } if $scm_only; then if test ! -e .scmversion; then res=$(scm_version) echo "$res" >.scmversion fi exit fi if test -e include/config/auto.conf; then . include/config/auto.conf else echo "Error: kernelrelease not valid - run 'make prepare' to update it" exit 1 fi # localversion* files in the build and source directory res="$(collect_files localversion*)" if test ! "$srctree" -ef .; then res="$res$(collect_files "$srctree"/localversion*)" fi # CONFIG_LOCALVERSION and LOCALVERSION (if set) res="${res}${CONFIG_LOCALVERSION}${LOCALVERSION}" # scm version string if not at a tagged commit if test "$CONFIG_LOCALVERSION_AUTO" = "y"; then # full scm version string res="$res$(scm_version)" else # append a plus sign if the repository is not in a clean # annotated or signed tagged state (as git describe only # looks at signed or annotated tags - git tag -a/-s) and # LOCALVERSION= is not specified if test "${LOCALVERSION+set}" != "set"; then scm=$(scm_version --short) res="$res${scm:++}" fi fi # add by *,save git commit id to ./include/generated/git_ver.h rm -rf "$srctree"/include/generated/git_ver.h GIT_VER_INC_PATH="$srctree/include/generated/git_ver.h" // 将git commit ID导出到git_ver.h中 echo "/*" >> $GIT_VER_INC_PATH echo "* auto generate. Don't edit!" >> $GIT_VER_INC_PATH echo "*/" >> $GIT_VER_INC_PATH echo "#ifndef __GIT_VERSION_H__" >> $GIT_VER_INC_PATH echo >> $GIT_VER_INC_PATH echo "#define __GIT_VERSION_H__" >> $GIT_VER_INC_PATH echo >> $GIT_VER_INC_PATH echo "#define GIT_COMMIT_ID_STR \"$(scm_version)\" ">> $GIT_VER_INC_PATH echo >> $GIT_VER_INC_PATH echo "#endif" >> $GIT_VER_INC_PATH echo "$res"上述代码红色部分是修改的地方，编译linux内核以后，自动生成的git_ver.h如下：
/* * auto generate. Don't edit! */ #ifndef __GIT_VERSION_H__ #define __GIT_VERSION_H__ #define GIT_COMMIT_ID_STR "afb275c" // 可以通过git show afb275c，方便的查询这个版本的log #endif
3. 从git_ver.h中获取git commit ID，并打印，且存放到到 /proc/version文件系统中
linux启动时，start_kernel()函数会打印版本号
init/main.c:asmlinkage void __init start_kernel(void) { ...... boot_cpu_init(); page_address_init(); pr_notice("%s", linux_banner); ...... } linux_banner的定义： init/version.c:/* FIXED STRINGS! Don't touch! */ const char linux_banner[] = "Linux version " UTS_RELEASE " (" LINUX_COMPILE_BY "@" LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION "\nGit commit id: " GIT_COMMIT_ID_STR "\n"; // 再次全局变量中增加git commit ID用于显示 const char linux_proc_banner[] = "%s version %s" " (" LINUX_COMPILE_BY "@" LINUX_COMPILE_HOST ")" " (" LINUX_COMPILER ") %s\n""Git commit id: " GIT_COMMIT_ID_STR"\n";除了初始化打印，/proc/version文件系统中也提供版本相关的信息，正好用到linux_proc_banner变量，也添加上git commit ID
fs/proc/version.c:#include <linux/fs.h> #include <linux/init.h> #include <linux/kernel.h> #include <linux/proc_fs.h> #include <linux/seq_file.h> #include <linux/utsname.h> static int version_proc_show(struct seq_file *m, void *v) { seq_printf(m, linux_proc_banner, utsname()->sysname, utsname()->release, utsname()->version); return 0; } static int version_proc_open(struct inode *inode, struct file *file) { return single_open(file, version_proc_show, NULL); } static const struct file_operations version_proc_fops = { .open = version_proc_open, .read = seq_read, .llseek = seq_lseek, .release = single_release, }; static int __init proc_version_init(void) { proc_create("version", 0, NULL, &version_proc_fops); return 0; } fs_initcall(proc_version_init);4.修改后的结果
（1）串口打印：
Starting kernel ...machid 0, r2(bi_boot_params): 16ffa000gd 1fb8df38, bd 1fb8dfe0 bi_arch_number: 0kernel entry 00008000Booting Linux on physical CPU 0x0Linux version 3.14.0-xilinx (****@ubuntu) (gcc version 4.8.3 20140320 (prerelease) (Sourcery CodeBench Lite 2014.05-23) ) #8 SMP PREEMPT Mon Dec 12 11:28:17 CST 2016Git commit id: afb275c
（2）/proc/version
zynq> cat /proc/version Linux version 3.14.0-xilinx (liuwanpeng@ubuntu) (gcc version 4.8.3 20140320 (prerelease) (Sourcery CodeBench Lite 2014.05-23) ) #8 SMP PREEMPT Mon Dec 12 11:28:17 CST 2016Git commit id: afb275c
OK，job‘s done !
转载于:https://www.cnblogs.com/liuwanpeng/p/6164565.html
