Add linkerscript (experimental)

x1/linkerscript/crt0.s

@@ -0,0 +1,41 @@
+.text
+.arm
+.align 4
+
+.global _start
+_start:
+    stmdb   sp!, {r4, lr}
+    /* store context */
+    movs    r4, r0
+
+    /* Clear the .bss section */
+    bl      .L_clean_bss
+
+    /* restore context */
+    adr     r0, [.L_context]
+    str     r4, [r0]
+    ldr     r0, [r0]
+
+    /* call user's main */
+    bl      main
+
+    ldmia   sp!, {r4, pc}
+
+.L_context:
+.long 0
+
+/*
+    r0 = start address
+    r1 = end address
+    tmp: r2
+*/
+.L_clean_bss:
+    ldr     r0, =__bss_start
+    ldr     r1, =__bss_end
+    sub     r1, r1, #4
+    mov     r2, #0
+.L_clean_bss_loop:
+    cmp     r0, r1
+    strlt   r2, [r0], #4
+    blt     .L_clean_bss_loop
+    bx      lr