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Revision as of 03:50, 13 December 2017
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Embedded Linux Notes
this wiki article created 2017-12-11 Monday
Contents
Overview
This wiki document is a collection of Ted's notes on embedded Linux studies, with a starting point of building a recipe for a Linux system to run on a RaspberryPi 2 target hardware platform. Near term goal is to build a customized Linux 4.x kernel and test that it runs on a RaspberryPi dev board. Long term goal has two parts: (1) build a more useful Linux system with working C and C++ toolchain, networking stack, web server, e-mail and database server support, an X server or comparable graphics and desktop support, and (2) target other hardware platforms beyond RaspberryPi 2 board.
As of 2017-12-11 these notes are a mess, so Ted reviewing work so far and here starting summary of what's important, what has worked, what best steps known today to take going forward. First the major pieces we are finding and using:
- cross-compiling toolchain, e.g. Linaro gcc
- QEMU system hardware emulator
The cross-compiler and related tools we use to build our kernel and 'target' a.k.a. 'guest' system softwares. The guest system in our case is a Linux kernel and additional programs compiled to run together as a complete system on an ARM based processor, in the target hardware which is the RaspberryPi 2 board. We cross compile in order to get the much faster compilation times available on a typical cerca 2010 Intel desktop computer. The QEMU software allows us to experiment, jumping through some hoops, with our ARM-targeted kernels and softwares, without a physical RaspberryPi board present. We also get to skip the step of creating a system image and flashing that to SD card. Knowing how to create an SD-card-ready image, however, is important. We'll return to this we hope sooner than later, once we have seen our cross-compiled system pieces run in normal expected ways in QEMU's target hardware emulating environment.
Our target system software pieces for a basic Linux operating system include:
- Linux kernel 4.x
- device tree binary (dtb file)
- kernel modules
- root file system
Kernel, device trees and kernel modules are all part of the official operating system space. These three pieces get compiled when configuring Linux kernel for a RaspberryPi target board, using the kernel's arch/arm/configs/bcm2709_defconfig default configuration file. Our needed root file system is a separate matter, which we must built separately. We also have a number of options for how to configure and specify what we want to build in this file system.
As of this Monday, Ted finds good notes at a page of Azeria Labs and also a post by graduate student MedicineYeh. Ted finds a little more success from Azeria Labs article, getting QEMU invocations to bring up an already-compiled QEMU Linux kernel for ARM. But Ted's custom compiled 4.x kernels haven't booted yet, and no diagnostics messages visible save four lines relating to some kind of sound card module. MedicineYeh's blog post goes into more details about root file systems and a couple of ways to build them quickly for basic testing and practice, but so far none of his example calls to QEMU have worked. These all hang and time-out without any diagnostics feedback. MedicineYeh's blog post seems to imply in its QEMU output captures that QEMU can put guest system message to the shell which invoked QEMU. But it's not clear to Ted how this would happen, and it doesn't appear to happen by default. QEMU will present the ARM-targeted kernel with a device tree that's expressed in the device tree binary file that the Linux kernel arch' ARM default configuration describes somewhere under the hood . . . that device tree is different and separate from the host's device tree, including the host system's.
Regarding QEMU passing guest kernel message to standard out, there's mention in Azeria Labs article about QEMU option and argument -serial stdio. Ted to try this once he has kernel, dtb file, kernel modules and rootfs all cross-compiled for ARM on Ubuntu host . . .
^ New section - Trouble points
Two trouble points as of 2017-12-11 Monday. One, we're not seeing guest system messages in any of invoking shell, QEMU window, nor Remmina VNC client window. Ted wants to see guest system diagnostics at QEMU-invoking shell prompt. Two, Ted unsure whether we're mounting a rootfs properly in our call to QEMU.
Figure x - problems building and running Linux for ARM under QEMU
- guest kernel diagnostics not visible
- questions about passing rootfs to QEMU properly
^ RaspberryPi Kernel Compilation
- 2017-11-25 SAT - These notes are of first efforts to cross-compile Linux kernel and device tree blob, on Intel i386/i686 host system, for target ARM system specifically RaspberryPi 2 dev board. As of 2017-DEC-09 Saturday, four or five custom kernel configurations with rpi target chosen / in mind have failed, for reasons such as "enermation or pound define value not an integer" and "alignment type of variable x not available [on target processor]". Ted noting that the Linux kernel stable release with all its options and supported target hardware platforms and peripherals is heavyweight, not by default configured to be small or simple as possible. Now also looking into Tiny Kernel wiki page and home page of Tiny Core Linux.
Here are instructions for compiling and for cross-compiling a Linux kernel for RaspberryPi target system:
Here are limited instructions on how to configure the Linux kernel for RaspberryPi target systems:
Back in 2017 February this year, February 24th just after Embedded Linux Conference, looks like Ted stepped through some of the instructions at this Raspberry Pi dot org documentation page. Ted noting there are two directories on compiling host in /mnt with this timestamp:
ted@localhost:/mnt$ ls -l make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- menuconfig total 44 drwxr-xr-x 2 root root 4096 Oct 24 2016 dvd-rom drwxr-xr-x 2 root root 4096 Feb 24 2017 ext4 drwxr-xr-x 2 root root 4096 Feb 24 2017 fat32 . . .
When issuing the cross-compile command that task seemed to complete quickly, giving the following messages which total less than two hundred lines:
ted@rangari:~/projects/raspberrypi/linux$ make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- bcm2709_defconfig # # configuration written to .config # ted@rangari:~/projects/raspberrypi/linux$ make -j 2 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- zImage modules dtbs scripts/kconfig/conf --silentoldconfig Kconfig CHK include/config/kernel.release CHK include/generated/uapi/linux/version.h CHK include/generated/utsrelease.h HOSTCC scripts/dtc/dtc.o HOSTCC scripts/dtc/flattree.o HOSTCC scripts/dtc/fstree.o HOSTCC scripts/dtc/data.o HOSTCC scripts/dtc/livetree.o HOSTCC scripts/dtc/treesource.o HOSTCC scripts/dtc/srcpos.o make[1]: 'include/generated/mach-types.h' is up to date. CHK include/generated/timeconst.h CHK include/generated/bounds.h CHK include/generated/asm-offsets.h CALL scripts/checksyscalls.sh HOSTCC scripts/dtc/checks.o make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- menuconfig HOSTCC scripts/dtc/util.o HOSTCC scripts/dtc/dtc-lexer.lex.o HOSTCC scripts/dtc/dtc-parser.tab.o HOSTLD scripts/dtc/dtc HOSTCC scripts/genksyms/genksyms.o HOSTCC scripts/genksyms/parse.tab.o HOSTCC scripts/mod/mk_elfconfig HOSTCC scripts/genksyms/lex.lex.o MKELF scripts/mod/elfconfig.hhttps://www.raspberrypi.org/forums/viewtopic.php?f=66&t=178806 HOSTCC scripts/mod/modpost.o HOSTLD scripts/genksyms/genksyms HOSTCC scripts/kallsyms HOSTCC scripts/mod/file2alias.o HOSTCC scripts/pnmtologo HOSTCC scripts/conmakehash make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- menuconfig HOSTCC scripts/mod/sumversion.o HOSTCC scripts/recordmcount HOSTLD scripts/mod/modpost HOSTCC scripts/sortextable HOSTCC usr/gen_init_cpio CHK include/generated/compile.h GEN usr/initramfs_data.cpio.gz HOSTCC arch/arm/vdso/vdsomunge AS usr/initramfs_data.o LD usr/built-in.o MUNGE arch/arm/vdso/vdso.so.dbg OBJCOPY arch/arm/vdso/vdso.so AS arch/arm/vdso/vdso.o LD arch/arm/vdso/built-in.o GZIP kernel/config_data.gz make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- menuconfig CHK kernel/config_data.h HOSTCC lib/gen_crc32table HOSTCC lib/raid6/mktables TABLE lib/raid6/tables.c CC [M] lib/raid6/tables.o LD [M] lib/raid6/raid6_pq.o GEN lib/crc32table.h CC lib/crc32.o LD lib/built-in.o LOGO drivers/video/logo/logo_linux_clut224.c LOGO drivers/video/logo/logo_linux_mono.c LOGO drivers/video/logo/logo_superh_mono.c make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- menuconfig LOGO drivers/video/logo/logo_superh_vga16.c make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- menuconfig LOGO drivers/video/logo/logo_linux_vga16.c LOGO drivers/video/logo/logo_blackfin_vga16.c LOGO drivers/video/logo/clut_vga16.c LOGO drivers/video/logo/logo_spe_clut224.c LOGO drivers/video/logo/logo_mac_clut224.c LOGO drivers/video/logo/logo_superh_clut224.c LOGO drivers/video/logo/logo_sun_clut224.c LOGO drivers/video/logo/logo_parisc_clut224.c LOGO drivers/video/logo/logo_blackfin_clut224.c LOGO drivers/video/logo/logo_dec_clut224.c LOGO drivers/video/logo/logo_m32r_clut224.c LOGO drivers/video/logo/logo_sgi_clut224.c CC drivers/video/logo/logo_linux_clut224.o LD drivers/video/logo/built-in.o LD drivers/video/built-in.o make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- menuconfig LD drivers/built-in.o LINK vmlinux LD vmlinux.o MODPOST vmlinux.o GEN .version CHK include/generated/compile.h UPD include/generated/compile.h CC init/version.o LD init/built-in.o KSYM .tmp_kallsyms1.o KSYM .tmp_kallsyms2.o LD vmlinux SORTEX vmlinux SYSMAP System.map OBJCOPY arch/arm/boot/Image Building modules, stage 2. Kernel: arch/arm/boot/Image is ready Kernel: arch/arm/boot/Image is ready GZIP arch/arm/boot/compressed/piggy.gzip AS arch/arm/boot/compressed/piggy.gzip.o LD arch/arm/boot/compressed/vmlinux OBJCOPY arch/arm/boot/zImage Kernel: arch/arm/boot/zImage is ready MODPOST 1540 modules LD [M] lib/raid6/raid6_pq.ko ted@rangari:~/projects/raspberrypi/linux$
At this point it looks like we may have enough to attempt the qemu invocation which was partially working off site west side, since couple days ago we were missing what appeared to be only the kernel when invoking qemu on build box rangari . . .
So we can launch Raspbian for the RaspberryPi 2 board, using a kernel we've built on an i386 architecture host server, using the default bcmp_2907 (mis-spelled) kernel config file. But we can't fully compile a kernel for an ARM / Rpi target architecture when we make any kernel configuration changes via `make menuconfig`. The script which successfully starts our qemu-system-arm version 2.10.0 is:
#!/bin/bash qemu-system-arm -kernel ./kernel-qemu-4.4.34-jessie -cpu arm1176 -m 256 -M versatilepb -serial stdio -append "root=/dev/sda2 rootfstype=ext4 rw" -hda ./2017-09-07-raspbian-stretch-lite.img -redir tcp:5022::22 -no-reboot exit 0
Right now this script is located along side several already compiled, ARM-targeted kernels which Ted believes are from the git available cross-compile Rpi project by one 'dhruvvyas90' . . . Dhruvvyas90 qemu-rpi-kernel.
ted@localhost:/var/local/ted/projects/raspberrypi/qemu_vms$ ls 2017-09-07-raspbian-stretch-lite.img kernel-qemu-4.1.7-jessie kernel-qemu-4.4.21-jessie README.md kernel-qemu-3.10.25-wheezy kernel-qemu-4.4.12-jessie kernel-qemu-4.4.26-jessie start-qemu.sh kernel-qemu-4.1.13-jessie kernel-qemu-4.4.13-jessie kernel-qemu-4.4.34-jessie tools ted@localhost:/var/local/ted/projects/raspberrypi/qemu_vms$
- Summary rpi kernel compilations -
As of 2017 Dec 2 we can using QEMU 2.10.0 boot and use Raspbian image and kernel from Raspberry Pi on-line store. We can also substitute alternate kernel in call to QEMU system emulator, a kernel from . . .
^ edit point - custom Rpi-targeted kernel config issues
- 2017-11-30 -
In file included from ./include/uapi/linux/stddef.h:1:0,
from ./include/linux/stddef.h:4,
from ./include/uapi/linux/posix_types.h:4,
from ./include/uapi/linux/types.h:13,
from ./include/linux/types.h:5,
from fs/xfs/xfs_linux.h:21,
from fs/xfs/xfs.h:32,
from fs/xfs/xfs_super.c:19:
In function ‘xfs_check_ondisk_structs’,
inlined from ‘init_xfs_fs’ at fs/xfs/xfs_super.c:1974:2:
./include/linux/compiler.h:518:38: error: call to ‘__compiletime_assert_119’ declared with attribute error: XFS: sizeof(xfs_dir2_sf_entry_t) is wrong, expected 3
_compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
^
./include/linux/compiler.h:501:4: note: in definition of macro ‘__compiletime_assert’
prefix ## suffix(); \
^
./include/linux/compiler.h:518:2: note: in expansion of macro ‘_compiletime_assert’
_compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
^
./include/linux/bug.h:54:37: note: in expansion of macro ‘compiletime_assert’
#define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
^
fs/xfs/xfs_ondisk.h:22:2: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
BUILD_BUG_ON_MSG(sizeof(structname) != (size), "XFS: sizeof(" \
^
fs/xfs/xfs_ondisk.h:119:2: note: in expansion of macro ‘XFS_CHECK_STRUCT_SIZE’
XFS_CHECK_STRUCT_SIZE(xfs_dir2_sf_entry_t, 3);
^
scripts/Makefile.build:293: recipe for target 'fs/xfs/xfs_super.o' failed
make[2]: *** [fs/xfs/xfs_super.o] Error 1
scripts/Makefile.build:544: recipe for target 'fs/xfs' failed
make[1]: *** [fs/xfs] Error 2
Makefile:991: recipe for target 'fs' failed
make: *** [fs] Error 2
real 17m33.542s
user 16m10.988s
sys 0m53.000s
Ok as of 2017-12-08 and a few days ago Ted realizing that the `make menuconfig` type call to configure a Linux kernel for a RaspberryPi/Arm target architecture must be of the form:
$ make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- menuconfig
Now again calling the version of this command with options to compile kernel, device tree binary, and modules:
$ make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- zImage modules dtbs
^ edit point - further references for kernel configuration wrt RaspberryPi target
Ted found these references in the README.md file of QEMU Rpi Tools project. Local directory is qemu-rpi-kernel/. Invoking `git status .` shows this to be a git repository. Invoking `git remote -v` shows this repository to be a clone of:
ted@localhost:~/projects/qemu/qemu-rpi-kernel$ git remote -v origin https://github.com/dhruvvyas90/qemu-rpi-kernel.git (fetch) origin https://github.com/dhruvvyas90/qemu-rpi-kernel.git (push) ted@localhost:~/projects/qemu/qemu-rpi-kernel$ #
In the READ.md file the Rpi kernel project author who doesn't identify him or herself lists the following four references together, and there are a couple more refs beyond these mentioned near the end of READ.md:
https://web.archive.org/web/20131210001638/http://xecdesign.com/compiling-a-kernel/ https://web.archive.org/web/20131209235952/http://xecdesign.com/compiling-qemu/ https://web.archive.org/web/20131210001407/http://xecdesign.com/working-with-qemu/ https://web.archive.org/web/20131210001526/http://xecdesign.com/qemu-emulating-raspberry-pi-the-easy-way/
^ Rpi kernel configuration further references
- https://www.raspberrypi.org/forums/viewtopic.php?t=125085&p=839033 . . . shows use of `dpkg-query -l` to find kernel version details on Linux system.
^ general kernel configuration and compile reference
- 2017-12-05 - Ted adding section on general articles, some non-Rpi articles and reference materials which explain how to configure a kernel and then how to invoke the build process and point `make` to the new custom configuration file. This so far not clear from the instructions at Raspberry Pi's articles https://www.raspberrypi.org/documentation/linux/kernel/building.md and https://www.raspberrypi.org/documentation/linux/kernel/configuring.md. These references found at Google via search phrase "invoking make after custom kernel configuration":
^ Buildroot
Per Medicine Yeh's tutorial setting out to compile and use buildroot project, to create Linux based root file system to run under QEMU. Mid-way messages from `make` call on buildroot project downloaded from git repository:
/usr/bin/install -m 0644 support/misc/target-dir-warning.txt /var/local/ted/projects-on-slash-var/buildroot/buildroot/output/target/THIS_IS_NOT_YOUR_ROOT_FILESYSTEM >>> skeleton-init-sysv Extracting >>> skeleton-init-sysv Patching >>> skeleton-init-sysv Configuring >>> skeleton-init-sysv Building >>> skeleton-init-sysv Installing to target rsync -a --ignore-times --exclude .svn --exclude .git --exclude .hg --exclude .bzr --exclude CVS --chmod=u=rwX,go=rX --exclude .empty --exclude '*~' package/skeleton-init-sysv//skeleton/ /var/local/ted/projects-on-slash-var/buildroot/buildroot/output/target/ >>> skeleton Extracting >>> skeleton Patching >>> skeleton Configuring >>> skeleton Building >>> skeleton Installing to target >>> linux-headers 4.14.4 Downloading --2017-12-09 23:11:28-- https://cdn.kernel.org/pub/linux/kernel/v4.x/linux-4.14.4.tar.xz Resolving cdn.kernel.org (cdn.kernel.org)... 151.101.53.176, 2a04:4e42:d::432 Connecting to cdn.kernel.org (cdn.kernel.org)|151.101.53.176|:443... connected. HTTP request sent, awaiting response... 200 OK Length: 100784788 (96M) [application/x-xz] Saving to: ‘/var/local/ted/projects-on-slash-var/buildroot/buildroot/output/build/.linux-4.14.4.tar.xz.VsSH6c/output’
Tail message from `make` on buildroot project:
chmod a+x /var/local/ted/projects-on-slash-var/buildroot/buildroot/output/build/buildroot-fs/fakeroot.fs rm -f /var/local/ted/projects-on-slash-var/buildroot/buildroot/output/target/THIS_IS_NOT_YOUR_ROOT_FILESYSTEM PATH="/var/local/ted/projects-on-slash-var/buildroot/buildroot/output/host/bin:/var/local/ted/projects-on-slash-var/buildroot/buildroot/output/host/sbin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:/sbin:/usr/sbin:/opt/cross/bin:/opt/cross/x-tools/arm-unknown-linux-gnueabi/bin:/home/ted/bin:/usr/local/mysql/bin:/usr/lib/xscreensaver:/etc/init.d:/var/opt/sam-ba_cdc_cdc_linux" /var/local/ted/projects-on-slash-var/buildroot/buildroot/output/host/bin/fakeroot -- /var/local/ted/projects-on-slash-var/buildroot/buildroot/output/build/buildroot-fs/fakeroot.fs rootdir=/var/local/ted/projects-on-slash-var/buildroot/buildroot/output/target table='/var/local/ted/projects-on-slash-var/buildroot/buildroot/output/build/buildroot-fs/device_table.txt' /usr/bin/install -m 0644 support/misc/target-dir-warning.txt /var/local/ted/projects-on-slash-var/buildroot/buildroot/output/target/THIS_IS_NOT_YOUR_ROOT_FILESYSTEM real 48m56.055s user 53m27.352s sys 4m47.896s ted@rangari:/var/local/ted/projects/buildroot/buildroot$
^ Putting The Pieces Together - QEMU, kernel, rootfs
On our day host system we need and have a cross-compiler, a guest system emulator, a cross-compiled Linux 4.x kernel, a corresponding device tree binary and a root file system . . .
cross-compiler ~/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian/bin qemu /usr/local/bin/qemu-system-arm kernel /var/local/raspberrypi/linux/arch/arm/boot/zImage device tree binary /var/local/raspberrypi/linux/arch/arm/boot/dts/[ bcm2709-rpi-2-b.dtb | bcm2836-rpi-2-b.dtb | ... ] not sure which dtb to use! - TMH root file system ...
One root file system we have which is part of a successful QEMU boot of a guest Raspbian system is the ~1.85GB raspbian stretch lite image, md5 check sum noted here:
projects-on-slash-var/raspberrypi/qemu_vms$ md5sum /var/local/ted/downloads/raspberrypi/2017-09-07-raspbian-stretch-lite.img 2d5f26a5c75ea7e5677542a3411851e3 /var/local/ted/downloads/raspberrypi/2017-09-07-raspbian-stretch-lite.img
Per Azeria Labs tutorial on emulating RaspberryPi operating system and hardware, a prerequisite step which modifies a system "reach run level" time must be modified. To modify a file in a disk image file we mount the image file in a manner like,
$ sudo mount -v -o offset=47185920 -t ext4 /var/local/raspberrypi/file-system-images/2017-04-10-raspbian-jessie.img /mnt/raspbian [sudo] password for user: mount: /dev/loop0 mounted on /mnt/raspbian. $
^ QEMU references
- https://lists.gnu.org/archive/html/qemu-discuss/2014-09/msg00060.html . . . example qemu-system-arm invocations
# qemu-system-arm -kernel arch/arm/boot/zImage -dtb rtsm_ve-cortex_a15x4.dtb -m 512 -M vexpress-a15 -serial stdio -append "console=ttyAMA0"
Extra Notes on QEMU
Gosh frustrating, we were just practicing with calling QEMU in the following way (figure x) which follows the form of invocations we have seen in multiple tutorials and forum posts. Nearly all calls fail with a two lines "audio: Could not init `oss' audio driver . . . Could not read keymap file: 'en-us'". Ted suspected these might be errors coming from the kernel starting up in QEMU, and thought to change the kernel to an earlier release in the pre-compiled kernels of Dhruvvyas. This thought led to choosing a non-existent kernel filename and trying that out in call to QEMU. This made no difference! Same error messages, looks like QEMU doesn't get to the point of sanity checking or needing a valid kernel file name. So how can we debug this failure to boot a kernel plus root filesystem for RaspberryPi "guest" platform? What program or executing code are we actually wanting to debug?
Figure x - QEMU invocation which fails with or without kernel . . .
$ qemu-system-arm -M versatilepb -cpu arm1176 -m 256 -serial stdio -kernel /var/local/raspberrypi/qemu-rpi-kernel/kernel-qemu-4.4.34-jessiez -dtb /var/local/raspberrypi/linux/arch/arm/boot/dts/bcm2709-rpi-2-b.dtb -append "root=/dev/sda2 rootfstype=ext4 rw init=/bin/bash console=ttyAMA0" -drive format=raw,file=/home/veris/Downloads/raspberrypi/2017-08-16-raspbian-stretch-lite.img audio: Could not init `oss' audio driver Could not read keymap file: 'en-us' $
References
