riscv64-unknown-elf-gcc -S -m32 test.c

test.c:

int main() {
	extern start();
	start();
}
--

GCC:s assembly output:

	.file	"test.c"
	.option nopic
	.attribute arch, "rv64i2p0_m2p0_a2p0_f2p0_d2p0_c2p0"
	.attribute unaligned_access, 0
	.attribute stack_align, 16
	.text
	.align	1
	.globl	main
	.type	main, @function
main:
	addi	sp,sp,-16
	sd	ra,8(sp)
	sd	s0,0(sp)
	addi	s0,sp,16   <<--- WHAT HAPPENS HERE?
	call	start
	li	a5,0                 <<-- AND HERE
	mv	a0,a5                <<-- AND HERE
	ld	ra,8(sp)
	ld	s0,0(sp)
	addi	sp,sp,16
	jr	ra
	.size	main, .-main
	.ident	"GCC: () 8.3.0"