ARM bare-metal test.

init.S

#define push(a...) stmdb r13!,{a}
#define pop(a...) ldmia r13!,{a}
#define PRINTK(STR)\
    push(r3,r4,r5,r14); \
    adr r4,1f; \
    bl  debugprint; \
    bl  2f; \
    1: .ASCIZ STR; \
    .ALIGN 4; \
    2: pop(r14,r5,r4,r3)
#define SERIAL0_BASE 0x10009000
#define SERIAL0_FLAG 0x10009018


.text
PRINTK("TEST\r\n")
1: b 1b

debugprint:
    ldr     r3,=SERIAL0_FLAG
1:  ldr     r5,[r3]
    ands    r5,#(1<<5)
    bne     1b
    ldr     r3,=SERIAL0_BASE
    ldrb    r5,[r4],#1
    cmp     r5,#0
    moveq   r15,r14
    str     r5,[r3]
    b       debugprint

link.ld

SECTIONS {
    . = 0x70001000;
    .text : { * (.text); }
}

Makefile

SOURCES=init.S
TARGET=os
BINDIR=bin/
AS=arm-unknown-linux-gnueabi-gcc
LD=arm-unknown-linux-gnueabi-ld
CC=arm-unknown-linux-gnueabi-cc
OBJDUMP=arm-unknown-linux-gnueabi-objdump
OBJCOPY=arm-unknown-linux-gnueabi-objcopy
OBJECTS=$(SOURCES:%.S=$(BINDIR)%.o)

all: $(TARGET).bin
    cp $(BINDIR)$(TARGET).bin $(BINDIR)disk.img

$(OBJECTS): $(BINDIR)%.o : ./%.S
    $(AS) -mcpu=cortex-a8 -ffreestanding -c $< -o $@

os.bin: $(OBJECTS)
    $(LD) -T link.ld $(OBJECTS) -o $(BINDIR)$(TARGET).elf
    $(OBJCOPY) $(BINDIR)$(TARGET).elf -O binary $(BINDIR)$(TARGET).bin

run: all
    qemu-system-arm -M realview-pb-a8 -m 512 -kernel $(BINDIR)disk.img -nographic -no-reboot -monitor telnet:127.0.0.1:2048,server,nowait,ipv4