5 Minute User Space “Hello, World!” ARM Cross Compile, Copy to a RootFS and Run on QEMU
This post shows you how to write a user space Hello, World! program, cross-compile it for ARM, copy into a Root FS and run the new Root FS on QEMU.
Before you Start
Read and follow the ARM instructions listed in 15 Minute Setup to Find, Change, Recompile and Test an ARM or x86 Linux Kernel Change in 12 Seconds at [link]
Steps
Create helloworld.c
1. Type cd ~/tla/linux-4.10.6
2. Type mkdir -p helloworld
3. Type cd helloworld
4. Type vi helloworld.c and enter:
#include <stdio.h>
int main(int argc, char *argv[])
{
printf("Hello, World!\n");
}
5. Save the file with :w and quit with :q
Compile It
1. Type cd ~/tla/linux-4.10.6
2. Type cd helloworld
3. Type arm-linux-gnueabi-gcc helloworld.c -o helloworld -static
4. Type ls -l
You should see the new exe
zpfeffer@z:~/tla/linux-4.10.6/helloworld$ ls -l
total 572
-rwxrwxr-x 1 zpfeffer zpfeffer 579368 Jan 4 23:09 helloworld
-rw-rw-r-- 1 zpfeffer zpfeffer 85 Jan 4 23:09 helloworld.c
Copy helloworld to the Rootfs Staging Area and repack the RootFS
1. Type cd ~/tla/linux-4.10.6
2. Type source ~/envset.sh
3. Type cd helloworld
4. Type cp -av helloworld $TOP/initramfs/arm-busybox
5. Create the initramfs
cd $TOP/initramfs/arm-busybox
find . | cpio -H newc -o > ../initramfs.cpio
cd ..
cat initramfs.cpio | gzip > $TOP/obj/initramfs.igz
Boot QEMU and Run helloworld
1. Type
STAGE=$HOME/tla
TOP=$STAGE/teeny-linux
qemu-system-arm -M versatilepb \
-dtb $TOP/obj/linux-arm-versatile_defconfig/arch/arm/boot/dts/versatile-pb.dtb \
-kernel $TOP/obj/linux-arm-versatile_defconfig/arch/arm/boot/zImage \
-initrd $TOP/obj/initramfs.igz \
-nographic -append "earlyprintk=serial,ttyS0 console=ttyAMA0"
2. After boot type ls /usr/bin check that helloworld is in /usr/bin
You should see:
/ # ls /usr/bin/
[ du last pgrep smemcap unix2dos
[[ dumpleases less pkill softlimit unlink
awk eject logger pmap sort unlzma
basename env logname printf split unlzop
beep envdir lpq pscan strings unshare
blkdiscard envuidgid lpr pstree sum unxz
bunzip2 expand lsof pwdx sv unzip
bzcat expr lspci readlink svc uptime
bzip2 fgconsole lsusb realpath tac users
cal find lzcat renice tail uudecode
chpst flock lzma reset tcpsvd uuencode
chrt fold lzopcat resize tee vlock
chvt free man rpm2cpio telnet volname
cksum ftpget md5sum runsv test wall
clear ftpput mesg runsvdir tftp wc
cmp fuser microcom rx time wget
comm groups mkfifo script timeout which
crontab hd mkpasswd seq top who
cryptpw head nc setkeycodes tr whoami
cut helloworld nmeter setsid traceroute whois
dc hexdump nohup setuidgid traceroute6 xargs
deallocvt hostid nsenter sha1sum truncate xz
diff id nslookup sha256sum tty xzcat
dirname install od sha3sum ttysize yes
dos2unix ipcrm openvt sha512sum udpsvd
dpkg ipcs passwd showkey unexpand
dpkg-deb killall patch shuf uniq
3. Run helloworld by typing helloworld
You should see:
/ # helloworld
Hello, World!
4. Type Control-a x to quit QEMU
References