Basics on ARM processor

I am also teaching "Laboratory of Microprocessors" focusing ARM. I use ARM Lab Manual for the first experiences. 

I have been asking students to install a tool chain in ubuntu to develop experiments in the simulator provided by arm-...-gdb. Last year, one team made everything as the docker image:
https://github.com/EpicEric/gcc-arm.git

In order to use it: 

• git clone https://github.com/EpicEric/gcc-arm.git
• See README.md 
• cd gcc-arm/
• ./build_docker.sh emacs # any other editor that you prefer; perhaps, you will need sudo,and perhaps gedit suchs as: 
•               sudo ./build_docker.sh gedit
• docker run --rm -ti -v "$PWD/src":/home/student/src epiceric/gcc-arm

Note that your directory $PWD/src is attached to /home/student/src.

In this docker image, we have 2 tool-chains: arm-elf and arm-none-eabi. In the first part of the course, we are using arm-elf. We will use arm-none-eabi to deal with the versatille board, emulated by qemu.

The environment contains the alias:

student:~/src$ alias 

alias alert='notify-send --urgency=low -i "$([ $? = 0 ] && echo terminal || echo error)" "$(history|tail -n1|sed -e '\''s/^\s*[0-9]\+\s*//;s/[;&|]\s*alert$//'\'')"'

alias arm='arm-elf-gcc -S'

alias e7t='arm-elf-gdb -tui --command=/home/student/.gdbinit/evaluator7t'

alias eabi-as='arm-none-eabi-as -c -mcpu=arm926ej-s -g'

alias eabi-bin='arm-none-eabi-objcopy -O binary'

alias eabi-gcc='arm-none-eabi-gcc -c -mcpu=arm926ej-s -Wall -Wextra -g'

alias eabi-gdb='arm-none-eabi-gdb -tui --command=/home/student/.gdbinit/default'

alias eabi-ld='arm-none-eabi-ld'

alias eabi-qemu='arm-none-eabi-gdb -tui --command=/home/student/.gdbinit/qemu'

alias egrep='egrep --color=auto'

alias fgrep='fgrep --color=auto'

alias gcc='arm-elf-gcc -Wall -Wextra -g'

alias gdb='arm-elf-gdb -tui --command=/home/student/.gdbinit/default'

alias grep='grep --color=auto'

alias l='ls -CF'

alias la='ls -A'

alias ll='ls -alF'

alias ls='ls --color=auto'

alias qemu='qemu-system-arm -M versatilepb -m 128M -nographic -s -S -kernel'

Let us one very silly program.

Edit hello.c:

void main() {

     printf("hello");

}

If you can not create hello.c, it must be due to permission. In this case, try:
~/gcc-arm$ chmod 777 src

Let us compile it:

arm-elf-gcc -Wall -g -o hello hello.c

-g: for debug in the ARM simulator provided by arm-elf-gdb:

To run and debug:

arm-elf-gdb hello

(gdb) target sim

(gdb) load

(gdb) break main

(gdb) run

(gdb) continue

Making "C-x A" (control-x A) you may see the following screen:

If you do: "C-x 2", you may see the C code or the machine code. Pretty cool, isn't it?

Compile hello.c to see the machine code as in:

arm-elf-gcc -S hello.c

which generates hello.s 

student:~/src$ arm-elf-gcc -S hello.c

hello.c: In function `main':

hello.c:1: warning: return type of 'main' is not `int'

student:~/src$ ls -alt |more

total 404

-rw-rw-r-- 1 student student    396 Apr 23 18:01 hello.s

See hello.s:

student:~/src$ more hello.s

.file "hello.c"

.section .rodata

.align 2

.LC0:

.ascii "hello\000"

.text

.align 2

.global main

.type main, %function

main:

@ args = 0, pretend = 0, frame = 0

@ frame_needed = 1, uses_anonymous_args = 0

mov ip, sp

stmfd sp!, {fp, ip, lr, pc}

sub fp, ip, #4

ldr r0, .L2

bl printf

ldmfd sp, {fp, sp, pc}

.L3:

.align 2

.L2:

.word .LC0

.size main, .-main

.ident "GCC: (GNU) 3.4.3"

You may use this file hello.s to generate the ARM executable file as in:

arm-elf-gcc -Wall -g -o alo hello.s