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[QEMU] Build linux for SoC board using ARM.md

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[QEMU] Build linux for SoC board using ARM.md

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In this tutorial, I will show you how to build a kernel with our toolchain.

Important note: Please follow the linux branch as the guide to ensure successfully of kernel as well as the root filesystem which will be guided in the next post.

Get the linux source code

git clone git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git

In the configuration of cross compiler, we use the linux version of v4.10.17 so we should checkout to that linux branch to avoid errors.

cd linux-stable
git checkout v4.10.17

Make the configuration file for a target board

There are a set of known working configuration files in <PATH>/arch/arm/configs, each containing suitable configuration values for a single SoC or a group of SoCs. You can select one with make configuration_file_name.

For example, to configure Linux to run on a wide range of SoCs using the armv7-a architecture, you would type:

	PATH=~/x-tools/arm-unknown-linux-gnueabi/bin:$PATH
	make ARCH=arm CROSS_COMPILE=arm-unknown-linux-gnueabi- multi_v7_defconfig

multi_v7_defconfig is a generic kernel that runs on various different boards. For a more specialized application, for example when using a vendor-supplied kernel, the default configuration file is part of the board support package; you will need to find out which one to use before you can build the kernel.

Again, you may want to change the default configuration in .config file by using the menuconfig or edit .config file.

	make ARCH=arm CROSS_COMPILE=arm-unknown-linux-gnueabi- menuconfig

I will keep it as default.

Build linux with zImage output

	make ARCH=arm CROSS_COMPILE=arm-unknown-linux-gnueabi- zImage

Check the kernel version: make kernelversion

Build dtbs

	make ARCH=arm CROSS_COMPILE=arm-unknown-linux-gnueabi- dtbs

After that, you already have zImage and dtb output in <PATH>/arch/arm/boot/ directory.

Run the zImage with vexpress-a9 board as the following commands:

	QEMU_AUDIO_DRV=none qemu-system-arm -m 256M -nographic -M vexpress-a9 -kernel arch/arm/boot/zImage -dtb arch/arm/boot/dts/vexpress-v2p-ca9.dtb -append "console=ttyAMA0"

The console would end up with the Kernel panic error because it can't find the rootfs which is the next jobs we have to build.

...
[    2.272285] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
[    2.272707] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.10.17 #1
[    2.272888] Hardware name: ARM-Versatile Express
[    2.274024] [<c030fed4>] (unwind_backtrace) from [<c030b4a8>] (show_stack+0x10/0x14)
[    2.274337] [<c030b4a8>] (show_stack) from [<c05aff5c>] (dump_stack+0x84/0x98)
[    2.274559] [<c05aff5c>] (dump_stack) from [<c03d4214>] (panic+0xd8/0x264)
[    2.274861] [<c03d4214>] (panic) from [<c1201218>] (mount_block_root+0x1b8/0x250)
[    2.275114] [<c1201218>] (mount_block_root) from [<c1201624>] (prepare_namespace+0x180/0x1c4)
[    2.275351] [<c1201624>] (prepare_namespace) from [<c1200e04>] (kernel_init_freeable+0x1c8/0x1d8)
[    2.276585] [<c1200e04>] (kernel_init_freeable) from [<c0c3cd18>] (kernel_init+0x8/0x10c)
[    2.276756] [<c0c3cd18>] (kernel_init) from [<c0307978>] (ret_from_fork+0x14/0x3c)
[    2.277493] ---[ end Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

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