Fedora 28 : ARM programming and testing .

This is a simple tutorial about ARM programming and QEMU:
The test.c program is this :

volatile unsigned int * const UART0DR = (unsigned int *)0x101f1000;
 
void print_uart0(const char *s) {
 while(*s != '\0') { /* Loop until end of string */
 *UART0DR = (unsigned int)(*s); /* Transmit char */
 s++; /* Next char */
 }
}
 
void c_entry() {
 print_uart0("Hello world!\n");
}

Using volatile keyword is necessary to instruct the compiler that the memory pointed.
The unsigned int type enforces 32-bits read and write access.
The QEMU model like in a real system on chip the Transmit FIFO Full flag must be checked in the UARTFR register before writing on the UARTDR register.
Create the startup.s assembler file:

.global _Reset
_Reset:
 LDR sp, =stack_top
 BL c_entry
 B .

Create the script linker named test.ld:

ENTRY(_Reset)
SECTIONS
{
 . = 0x10000;
 .startup . : { startup.o(.text) }
 .text : { *(.text) }
 .data : { *(.data) }
 .bss : { *(.bss COMMON) }
 . = ALIGN(8);
 . = . + 0x1000; /* 4kB of stack memory */
 stack_top = .;
}

Next step is the install of arm-none-eabi x86_64 tools :

[root@desk arm-source]# dnf install arm-none-eabi-gcc-cs-c++.x86_64 
Last metadata expiration check: 1:54:04 ago on Fri 15 Jun 2018 06:55:54 PM EEST.
Package arm-none-eabi-gcc-cs-c++-1:7.1.0-5.fc27.x86_64 is already installed, skipping.
Dependencies resolved.
Nothing to do.
Complete!
[root@desk arm-source]# dnf install arm-none-eabi-gdb.x86_64 
Last metadata expiration check: 1:54:48 ago on Fri 15 Jun 2018 06:55:54 PM EEST.
Package arm-none-eabi-gdb-7.6.2-4.fc24.x86_64 is already installed, skipping.
Dependencies resolved.
Nothing to do.
Complete!
[mythcat@desk arm-source]$ ll
total 12
-rw-rw-r--. 1 mythcat mythcat  60 Jun 15 20:28 startup.s
-rw-rw-r--. 1 mythcat mythcat 288 Jun 15 20:26 test.c
-rw-rw-r--. 1 mythcat mythcat 223 Jun 15 20:29 test.ld

Let's test this with qemu virtual tool ( use Ctr+A and X keys to stop qemu) :

[mythcat@desk arm-source]$ qemu-system-arm -M versatilepb -m 64M -nographic -kernel test.bin
pulseaudio: set_sink_input_volume() failed
pulseaudio: Reason: Invalid argument
pulseaudio: set_sink_input_mute() failed
pulseaudio: Reason: Invalid argument
Hello world!
QEMU: Terminated