working code v1

Makefile

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+CROSS_COMPILE = arm-none-eabi-
+
+build: start.S
+	$(CROSS_COMPILE)gcc -x assembler-with-cpp -c -O0 -g3 -mcpu=cortex-m4 -mthumb -Wall -o start.o start.S
+	$(CROSS_COMPILE)gcc start.o -mcpu=cortex-m4 -mthumb -Wall --specs=nosys.specs -nostdlib -lgcc -T./ldscript.ld -o start.elf
+	$(CROSS_COMPILE)objcopy -O binary -F elf32-littlearm start.elf start.bin
+
+qemu: build
+	qemu-system-gnuarmeclipse --verbose --verbose --board STM32F4-Discovery \
+		--mcu STM32F407VG -d unimp,guest_errors \
+		--semihosting-config enable=on,target=native -s -S \
+		--image start.bin
+
+clean:
+	rm *.o
+	rm *.elf
+	rm *.bin

ldscript.ld

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+MEMORY
+{
+    FLASH ( rx )  : ORIGIN = 0x08000000, LENGTH = 1M
+    RAM   ( rwx ) : ORIGIN = 0x20000000, LENGTH = 128K
+}
+
+__stack_start = ORIGIN(RAM) + LENGTH(RAM);

start.S

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+.syntax unified
+.cpu cortex-m4
+.thumb
+
+.global vtable
+.global reset_handler
+
+.type vtable, %object
+vtable:
+    .word __stack_start
+    .word __hard_reset__+1
+    .size vtable, .-vtable
+
+__hard_reset__:
+    ldr sp, =__stack_start
+    b __hard_reset__