rework structure

hifive1-vp/hello/bsp/env/start.S

@@ -0,0 +1,54 @@
+// See LICENSE for license details.
+
+	.section .init
+	.globl _start
+	.type _start,@function
+
+_start:
+	la gp, _gp
+	la sp, _sp
+
+	/* Load data section */
+	la a0, _data_lma
+	la a1, _data
+	la a2, _edata
+	bgeu a1, a2, 2f
+1:
+	lw t0, (a0)
+	sw t0, (a1)
+	addi a0, a0, 4
+	addi a1, a1, 4
+	bltu a1, a2, 1b
+2:
+
+	/* Clear bss section */
+	la a0, __bss_start
+	la a1, _end
+	bgeu a0, a1, 2f
+1:
+	sw zero, (a0)
+	addi a0, a0, 4
+	bltu a0, a1, 1b
+2:
+
+	/* Call global constructors */
+	la a0, __libc_fini_array
+	call atexit
+	call __libc_init_array
+
+#ifndef __riscv_float_abi_soft
+	/* Enable FPU */
+	li t0, MSTATUS_FS
+	csrs mstatus, t0
+	csrr t1, mstatus
+	and t1, t1, t0
+	beqz t1, 1f
+	fssr x0
+1:
+#endif
+
+	/* argc = argv = 0 */
+	li a0, 0
+	li a1, 0
+	call main
+	tail exit