yocto的hello world
为了辅助理解yocto编译的架构和编译过程，写一遍helloworld会好很多。
首先下载编译poky
$ git clone git://git.yoctoproject.org/poky
$ cd poky
$ source oe-init-build-env
$ bitbake core-image-sato
创建自己的layer：meta-mylayer
$ bitbake-layers create-layer meta-mylayer
NOTE: Starting bitbake server...
Add your new layer with 'bitbake-layers add-layer meta-mylayer'
在poky目录下通过bitbake-layers增加meta-layer，提示找不到bblayers.conf，原来是要在build目录下添加才对：
hui@hui:~/disk4t/codes/poky
$ bitbake-layers add-layer meta-mylayer
NOTE: Starting bitbake server...
Unable to find bblayers.conf
在build目录下add-layer, 没有指定meta-mylayer路径报错
hui@hui:~/disk4t/codes/poky/build
$ bitbake-layers add-layer meta-mylayer
NOTE: Starting bitbake server...
Specified layer directory /home/hui/disk4t/codes/poky/build/meta-mylayer doesn't exist
指定路径后可以了：
$ bitbake-layers add-layer ../meta-mylayer
NOTE: Starting bitbake server...
cat bblayer.conf可以看到meta-mylayer加到了最后一行
$ cat conf/bblayers.conf
# POKY_BBLAYERS_CONF_VERSION is increased each time build/conf/bblayers.conf
# changes incompatibly
POKY_BBLAYERS_CONF_VERSION = "2"
BBPATH = "${TOPDIR}"
BBFILES ?= ""
BBLAYERS ?= " \
/home/hui/disk4t/codes/poky/meta \
/home/hui/disk4t/codes/poky/meta-poky \
/home/hui/disk4t/codes/poky/meta-yocto-bsp \
/home/hui/disk4t/codes/poky/meta-mylayer \
"
查看meta-mylayer目录
$ tree .
.
├── conf
│ └── layer.conf
├── COPYING.MIT
├── README
└── recipes-example
└── example
└── example_0.1.bb
新建files目录，在files目录下添加hello.c文件
$ tree meta-mylayer/
meta-mylayer/
├── conf
│ └── layer.conf
├── COPYING.MIT
├── README
└── recipes-example
└── example
├── example_0.1.bb
└── files
└── hello.c
修改example_0.1.bb，定义编译规则
SUMMARY = "bitbake-layers recipe"
LICENSE = "MIT"
python do_display_banner() {
bb.plain("***********************************************");
bb.plain("* *");
bb.plain("* Example recipe created by bitbake-layers *");
bb.plain("* *");
bb.plain("***********************************************");
}
DESCRIPTION = "Simple helloworld application"
LICENSE = "MIT"
LIC_FILES_CHKSUM = "file://${COMMON_LICENSE_DIR}/MIT;md5=0835ade698e0bcf8506ecda2f7b4f302"
SRC_URI = "file://hello.c"
S = "${WORKDIR}"
do_compile() {
${CC} hello.c ${LDFLAGS} -o helloworld
}
do_install() {
install -d ${D}${bindir}
install -m 0755 helloworld ${D}${bindir}
}
编译
$ bitbake example
Loading cache: 100% |########################################################################################################################################################################| Time: 0:00:00
Loaded 1470 entries from dependency cache.
NOTE: Resolving any missing task queue dependencies
Build Configuration:
BB_VERSION = "1.51.1"
BUILD_SYS = "x86_64-linux"
NATIVELSBSTRING = "universal"
TARGET_SYS = "x86_64-poky-linux"
MACHINE = "qemux86-64"
DISTRO = "poky"
DISTRO_VERSION = "3.3+snapshot-bf47addb34debc049b59e5e466228f00045c2061"
TUNE_FEATURES = "m64 core2"
TARGET_FPU = ""
meta
meta-poky
meta-yocto-bsp
meta-mylayer = "master:bf47addb34debc049b59e5e466228f00045c2061"
Initialising tasks: 100% |###################################################################################################################################################################| Time: 0:00:00
Sstate summary: Wanted 0 Local 0 Network 0 Missed 0 Current 153 (0% match, 100% complete)
NOTE: Executing Tasks
NOTE: Tasks Summary: Attempted 623 tasks of which 623 didn't need to be rerun and all succeeded.
然后在tmp目录下find生成的Helloworld
$ find . -name "helloworld"
./work-shared/gcc-11.2.0-r0/gcc-11.2.0/libgo/misc/cgo/fortran/helloworld
./work/core2-64-poky-linux/gstreamer1.0/1.18.4-r0/gstreamer-1.18.4/tests/examples/helloworld
./work/core2-64-poky-linux/example/0.1-r0/packages-split/example/usr/bin/helloworld
./work/core2-64-poky-linux/example/0.1-r0/packages-split/example-dbg/usr/bin/.debug/helloworld
./work/core2-64-poky-linux/example/0.1-r0/package/usr/bin/.debug/helloworld
./work/core2-64-poky-linux/example/0.1-r0/package/usr/bin/helloworld
./work/core2-64-poky-linux/example/0.1-r0/image/usr/bin/helloworld
./work/core2-64-poky-linux/example/0.1-r0/helloworld
在conf/local.conf文件中增加IMAGE_INSTALL
IMAGE_INSTALL = "example"
IMAGE_INSTALL_append = "example",用IMAGE_INSTALL_append如下会报错，没有研究应该怎么用
$ bitbake core-image-sato
ERROR: Variable IMAGE_INSTALL_append contains an operation using the old override syntax. Please convert this layer/metadata before attempting to use with a newer bitbake.
然后build core-image-sato
$ bitbake core-image-sato
编译完成后再次运行，这次可能因为加了helloworld的缘故，没有进入到图形界面，但是在QEMU的shell环境中就可以运行helloworld程序，输出’Hello World!’。
$ runqemu tmp/deploy/images/qemux86-64/bzImage-qemux86-64.bin tmp/deploy/images/qemux86-64/core-image-sato-qemux86-64.ext4
参考：