I'm following a tutorial that offers this file (start.s),

.section ".text.boot"

.globl _start
_start:
   la sp, _stack_start
   call dstart
_hlt:
   j _hlt  # jump to _hlt

...assembled with this,
riscv64-unknown-elf-as -mno-relax -march=rv64imac start.s -c -o start.o

...which responds with,
start.s: Assembler messages:
start.s:1: Error: unrecognized opcode `.section ".text.boot"'

The only way I can get start.s to compile is by removing these first three lines:

.section ".text.boot"

.globl _start

Any help would be appreciated.