Set development environment with UART debug output for aarch64

Makefile

@@ -6,14 +6,13 @@ AARCH64_TOOLCHAIN ?= aarch64-linux-gnu
 # Shortcuts
 
 CC=clang --target=aarch64-none-elf -mcpu=cortex-a57
-# CC=$(AARCH64_TOOLCHAIN)-gcc
-LD=$(AARCH64_TOOLCHAIN)-ld
+LD=ld.lld
 OBJCOPY=$(AARCH64_TOOLCHAIN)-objcopy --target elf64-littleaarch64
 
 CFLAGS += -O0
 CFLAGS += -g
-CFLAGS += -nostdlib
-CFLAGS += -march=armv8-a
+#CFLAGS += -nostdlib
+#CFLAGS += -march=armv8-a
 #CFLAGS += -std=c99
 #CFLAGS += -pedantic
 #CFLAGS += -Wall
@@ -26,7 +25,7 @@ BUILD_DIR=build
 
 # Files
 
-KERNEL_MEMMAP = sys/memmap
+KERNEL_MEMMAP = aarch64/memmap
 
 KERNEL_SOURCES = \
   aarch64/boot.s \
@@ -45,7 +44,7 @@ kernel: $(BUILD_DIR)/kernel.elf # $(BUILD_DIR)/kernel.sym
 
 $(BUILD_DIR)/kernel.elf: $(KERNEL_OBJS)
 	$(info linking target: $@)
-	$(LD) -T$(KERNEL_MEMMAP) $^ -o $@
+	$(LD) -T$(KERNEL_MEMMAP) -nostdlib $^ -o $@
 	$(info done: $@)
 
 $(BUILD_DIR)/kernel.bin: $(BUILD_DIR)/kernel.elf
@@ -66,14 +65,15 @@ $(BUILD_DIR)/%.o: %
 # helpers
 QEMU_CMD = \
   qemu-system-aarch64 \
+    -M virt \
     -cpu cortex-a57 \
-    -machine type=virt \
     -nographic \
     -smp 4 \
-    -m 4098 \
+    -m 4096 \
     -kernel build/kernel.elf \
     -serial stdio \
-    -monitor none
+    -monitor none \
+
 
 clean:
 	rm -Rf ./$(BUILD_DIR)/*
@@ -83,4 +83,8 @@ run: kernel
 
 
 debug: kernel
-	$(QEMU_CMD) -gdb tcp::1234 -S
+	$(QEMU_CMD) -S -gdb tcp::1234 & \
+  gdb-multiarch -q \
+  -ex 'file build/kernel.elf' \
+  -ex 'target remote localhost:1234'
+	kill %1

aarch64/boot.S

@@ -1,22 +0,0 @@
-	.global _boot
-	.extern k_main
-
-
-_boot:
-	mrs x0, mpidr_el1       // Check CPU ID
-	mov x1, 0xC1000000
-	bic x0, x0, x1
-	cbz x0, set_stack
-	b idle
-
-set_stack:
-	ldr     x30, =0x40001000
-	mov     sp,  x30
-	bl      start
-
-start:
-	mov x0, x30
-	bl k_main
-
-idle: b idle
-

aarch64/boot.s

@@ -1,10 +1,7 @@
-	.text
-
 	.globl _start
-	.extern k_main
-	.extern stack_ptr 
 
 _start:
+
 	mrs x0, mpidr_el1       // Check CPU ID
 	mov x1, 0xC1000000
 	bic x0, x0, x1
@@ -12,13 +9,9 @@ _start:
 	b   idle
 
 set_stack:
-	ldr x30, stack_ptr  // defined in sys/memmap
+	ldr x30, =stack_ptr  // defined in sys/memmap
 	mov sp,  x30
-	bl  start
-
-start:
-	mov x0, x30
-	bl k_main
+	bl  k_main
 
 idle:
 	b idle

aarch64/memmap

@@ -0,0 +1,16 @@
+ENTRY(_start)
+
+SECTIONS
+{
+	/* For some reason qemu UART doesn't work with smaller address */
+	. = 0x40000000; 
+
+	.boot . : { boot.o(.text) }
+	.text : { *(.text) }
+	.data : { *(.data) }
+	.bss : { *(.bss COMMON) }
+
+	. = ALIGN(8);
+	. = . + 0x1000;
+	stack_ptr = . ;
+}

sys/main.c

@@ -25,13 +25,10 @@ k_main(void)
 {
 	uart_init();
 
-	uart_putc('L');
-	uart_putc('o');
-	uart_putc('w');
-	uart_putc('e');
-	uart_putc('\n');
+	uart_puts((unsigned char *) "Lowe OS\n");
 
 	for (;;) {
+		__asm__("WFE");
 	}
 }
 

sys/memmap

@@ -1,12 +0,0 @@
-    ENTRY(_start)
-
-    SECTIONS
-    {
-      . = 0x40000000;
-      .text : { *(.text) }
-      .data : { *(.data) }
-      .bss : { *(.bss COMMON) }
-      . = ALIGN(8);
-      . = . + 0x1000;
-      stack_ptr = . ;
-    }

sys/uart.c

@@ -15,7 +15,7 @@
 
 #include "uart.h"
 
-unsigned int *uart_base = (unsigned int *)UART_BASE;
+volatile unsigned int *UART0 = (unsigned int *)UART_BASE;
 
 
 void
@@ -24,10 +24,18 @@ uart_init(void)
 
 }
 
+
 void
 uart_putc(unsigned char c)
 {
-	*uart_base = c;
-	if(c == '\n')
-		*uart_base = '\r';
+	*UART0 = (unsigned int) c;
+}
+
+
+void
+uart_puts(const unsigned char *s)
+{
+	while(*s) {
+		*UART0 = (unsigned int) *(s++);
+	}
 }

sys/uart.h

@@ -22,9 +22,12 @@
 void
 uart_init(void);
 
+
 void
 uart_putc(unsigned char c);
 
 
+void
+uart_puts(const unsigned char *s);
 
 #endif /* !UART_H */