Bare-metal SERV C example

link.ld

/*
 * link.ld : Linker script for subservient SoC
 *
 * SPDX-FileCopyrightText: 2021 Olof Kindgren <olof.kindgren@gmail.com>
 * SPDX-License-Identifier: Apache-2.0
 */

OUTPUT_ARCH( "riscv" )
/*ENTRY(_start)*/

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

Makefile

#
# Makefile: Makefile for building subservient firmware
#
# SPDX-FileCopyrightText: 2021 Olof Kindgren <olof.kindgren@gmail.com>
# SPDX-License-Identifier: Apache-2.0
#
TOOLCHAIN_PREFIX ?= riscv64-unknown-elf-

%.elf: start.S %.c
	$(TOOLCHAIN_PREFIX)gcc -Os -march=rv32i -mabi=ilp32 -nostdlib -o $@ \
		-Wl,-Bstatic,-Tlink.ld $^

%.elf: %.S
	$(TOOLCHAIN_PREFIX)gcc -nostartfiles -march=rv32i -mabi=ilp32 -Tlink.ld -o$@ $<
%.hex: %.elf
	$(TOOLCHAIN_PREFIX)objcopy -O verilog $< $@
%.bin: %.elf
	$(TOOLCHAIN_PREFIX)objcopy -O binary $< $@
clean:
	rm -f *.elf *.bin *.hex

start.S

.section .text
_start:
	li sp, 0x300
	call main

sum.c

void main(void) {
  volatile int i;
  volatile int sum;
  for (i=0;i<100;i++)
    sum += i;
}