build-c.sh

arm-none-eabi-gcc \
	-nostdlib \
	-mcpu=cortex-m0plus \
	-mthumb \
	-Tlinker-script2.ld \
	-Wl,--entry=Reset_Handler \
	src/main.c \
	-o main.elf

arm-none-eabi-objcopy \
	-O binary \
	main.elf \
	main.bin

bossac -e -w -v main.bin -R

linker-script2.ld

/*
  Copyright (c) 2014-2015 Arduino LLC.  All right reserved.

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either
  version 2.1 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
  See the GNU Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public
  License along with this library; if not, write to the Free Software
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/

/* Linker script to configure memory regions.
 * Need modifying for a specific board.
 *   FLASH.ORIGIN: starting address of flash
 *   FLASH.LENGTH: length of flash
 *   RAM.ORIGIN: starting address of RAM bank 0
 *   RAM.LENGTH: length of RAM bank 0
 */
MEMORY
{
  FLASH (rx) : ORIGIN = 0x00000000+0x2000, LENGTH = 0x00040000-0x2000 /* First 8KB used by bootloader */
  RAM (rwx) : ORIGIN = 0x20000000, LENGTH = 0x00008000
}

/* Linker script to place sections and symbol values. Should be used together
 * with other linker script that defines memory regions FLASH and RAM.
 * It references following symbols, which must be defined in code:
 *   Reset_Handler : Entry of reset handler
 *
 * It defines following symbols, which code can use without definition:
 *   __exidx_start
 *   __exidx_end
 *   __copy_table_start__
 *   __copy_table_end__
 *   __zero_table_start__
 *   __zero_table_end__
 *   __etext
 *   __data_start__
 *   __preinit_array_start
 *   __preinit_array_end
 *   __init_array_start
 *   __init_array_end
 *   __fini_array_start
 *   __fini_array_end
 *   __data_end__
 *   __bss_start__
 *   __bss_end__
 *   __end__
 *   end
 *   __HeapLimit
 *   __StackLimit
 *   __StackTop
 *   __stack
 */
ENTRY(Reset_Handler)

SECTIONS
{
	.text :
	{
		__text_start__ = .;

		KEEP(*(.isr_vector))
		*(.text*)

		KEEP(*(.init))
		KEEP(*(.fini))

		/* .ctors */
		*crtbegin.o(.ctors)
		*crtbegin?.o(.ctors)
		*(EXCLUDE_FILE(*crtend?.o *crtend.o) .ctors)
		*(SORT(.ctors.*))
		*(.ctors)

		/* .dtors */
 		*crtbegin.o(.dtors)
 		*crtbegin?.o(.dtors)
 		*(EXCLUDE_FILE(*crtend?.o *crtend.o) .dtors)
 		*(SORT(.dtors.*))
 		*(.dtors)

		*(.rodata*)

		KEEP(*(.eh_frame*))
	} > FLASH

	.ARM.extab :
	{
		*(.ARM.extab* .gnu.linkonce.armextab.*)
	} > FLASH

	__exidx_start = .;
	.ARM.exidx :
	{
		*(.ARM.exidx* .gnu.linkonce.armexidx.*)
	} > FLASH
	__exidx_end = .;

	/* To copy multiple ROM to RAM sections,
	 * uncomment .copy.table section and,
	 * define __STARTUP_COPY_MULTIPLE in startup_ARMCMx.S */
	/*
	.copy.table :
	{
		. = ALIGN(4);
		__copy_table_start__ = .;
		LONG (__etext)
		LONG (__data_start__)
		LONG (__data_end__ - __data_start__)
		LONG (__etext2)
		LONG (__data2_start__)
		LONG (__data2_end__ - __data2_start__)
		__copy_table_end__ = .;
	} > FLASH
	*/

	/* To clear multiple BSS sections,
	 * uncomment .zero.table section and,
	 * define __STARTUP_CLEAR_BSS_MULTIPLE in startup_ARMCMx.S */
	/*
	.zero.table :
	{
		. = ALIGN(4);
		__zero_table_start__ = .;
		LONG (__bss_start__)
		LONG (__bss_end__ - __bss_start__)
		LONG (__bss2_start__)
		LONG (__bss2_end__ - __bss2_start__)
		__zero_table_end__ = .;
	} > FLASH
	*/

	__etext = .;

	.data : AT (__etext)
	{
		__data_start__ = .;
		*(vtable)
		*(.data*)

		. = ALIGN(4);
		/* preinit data */
		PROVIDE_HIDDEN (__preinit_array_start = .);
		KEEP(*(.preinit_array))
		PROVIDE_HIDDEN (__preinit_array_end = .);

		. = ALIGN(4);
		/* init data */
		PROVIDE_HIDDEN (__init_array_start = .);
		KEEP(*(SORT(.init_array.*)))
		KEEP(*(.init_array))
		PROVIDE_HIDDEN (__init_array_end = .);


		. = ALIGN(4);
		/* finit data */
		PROVIDE_HIDDEN (__fini_array_start = .);
		KEEP(*(SORT(.fini_array.*)))
		KEEP(*(.fini_array))
		PROVIDE_HIDDEN (__fini_array_end = .);

		KEEP(*(.jcr*))
		. = ALIGN(16);
		/* All data end */
		__data_end__ = .;

	} > RAM

	.bss :
	{
		. = ALIGN(4);
		__bss_start__ = .;
		*(.bss*)
		*(COMMON)
		. = ALIGN(4);
		__bss_end__ = .;
	} > RAM

	.heap (COPY):
	{
		__end__ = .;
		PROVIDE(end = .);
		*(.heap*)
		__HeapLimit = .;
	} > RAM

	/* .stack_dummy section doesn't contains any symbols. It is only
	 * used for linker to calculate size of stack sections, and assign
	 * values to stack symbols later */
	.stack_dummy (COPY):
	{
		*(.stack*)
	} > RAM

	/* Set stack top to end of RAM, and stack limit move down by
	 * size of stack_dummy section */
	__StackTop = ORIGIN(RAM) + LENGTH(RAM);
	__StackLimit = __StackTop - SIZEOF(.stack_dummy);
	PROVIDE(__stack = __StackTop);

	__ram_end__ = ORIGIN(RAM) + LENGTH(RAM) -1 ;

	/* Check if data + heap + stack exceeds RAM limit */
	ASSERT(__StackLimit >= __HeapLimit, "region RAM overflowed with stack")
}

main.c

extern unsigned int __stack;

typedef struct {
	void *initial_stack_pointer_value;
	void *reset_handler;

	char other_interrupt_vectors[42 * 4]; // space for 42 32-bit pointers
} VectorTable; 

void Reset_Handler();

__attribute__ ((section(".vectors")))
const VectorTable vector_table = {
	(void *)(&__stack),
	(void *)Reset_Handler,
};

void Reset_Handler() {
  // put your setup code here, to run once: (this code works when uploaded from the IDE)
  *(unsigned long *)0x41004408 = 131072ul;   // Set the direction of the port pin PA17 to an output
  *(unsigned long *)0x41004418 = 131072ul;   // Switch the output to 1 or HIGH
}