start.S

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/*-
 * Copyright (c) 2008 Semihalf, Rafal Czubak
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * $FreeBSD: releng/10.2/sys/boot/arm/uboot/start.S 283505 2015-05-25 01:06:55Z ian $
 */

#include <machine/asm.h>
#include <machine/armreg.h>

   .text
   .extern _C_LABEL(self_reloc), _C_LABEL(main)
   .weak   _DYNAMIC

/*
 * Entry point to the loader that U-Boot passes control to.
 */
   .globl  _start
_start:

#ifdef _ARM_ARCH_6
   mrc     p15, 0, ip, c1, c0, 0
   orr     ip, ip, #(CPU_CONTROL_UNAL_ENABLE)
   orr     ip, ip, #(CPU_CONTROL_AFLT_ENABLE)
   mcr     p15, 0, ip, c1, c0, 0
#endif
   /* 
    * Do self-relocation when the weak external symbol _DYNAMIC is non-NULL.
    * When linked as a dynamic relocatable file, the linker automatically
    * defines _DYNAMIC with a value that is the offset of the dynamic
    * relocation info section.
    * Note that we're still on u-boot's stack here, but the self_reloc 
    * code uses only a couple dozen bytes of stack space.
    */
   adr     ip, .here_off           /* .here_off is a symbol whose value */
   ldr     r0, [ip]                /* is its own offset in the text seg. */
   sub     r0, ip, r0              /* Get its pc-relative address and */
   ldr     r1, .dynamic_off        /* subtract its value and we get */
   teq     r1, #0                  /* r0 = physaddr we were loaded at. */
   addne   r1, r1, r0              /* r1 = dynamic section physaddr. */
   blne    _C_LABEL(self_reloc)    /* Do reloc if _DYNAMIC is non-NULL. */

   /* Hint where to look for the API signature */
   ldr     ip, =uboot_address
   str     sp, [ip]

   /* Save U-Boot's r8 and r9 */
   ldr     ip, =saved_regs
   str     r8, [ip, #0]
   str     r9, [ip, #4]

   /* 
    * Start loader.  This is basically a tail-recursion call; if main()
    * returns, it returns to u-boot (which reports the value returned r0).
    */
   b       main

   /* 
    * Data for self-relocation, in the text segment for pc-rel access.
    */
.here_off:
   .word   .
.dynamic_off:
   .word   _DYNAMIC

/*
 * syscall()
 */
ENTRY(syscall)
   /* Save caller's lr, r8 and r9 */
   ldr     ip, =saved_regs
   str     r8, [ip, #8]
   str     r9, [ip, #12]
   str     lr, [ip, #16]
   /* Restore U-Boot's r8 and r9 */
   ldr     r8, [ip, #0]
   ldr     r9, [ip, #4]
   /* Call into U-Boot */
   ldr     lr, =return_from_syscall
   ldr     ip, =syscall_ptr
   ldr     pc, [ip]
return_from_syscall:
   /* Restore loader's r8, r9 and lr */
   ldr     ip, =saved_regs
   ldr     lr, [ip, #16]
   ldr     r9, [ip, #12]
   ldr     r8, [ip, #8]
   /* Return to caller */
   mov     pc, lr

/*
 * Data section
 */
   .data
   .align  4
   .globl  syscall_ptr
syscall_ptr:
   .long   0

   .globl  uboot_address
uboot_address:
   .long   0

saved_regs:
   .long   0       /* U-Boot's r8 */
   .long   0       /* U-Boot's r9 */
   .long   0       /* Loader's r8 */
   .long   0       /* Loader's r9 */
   .long   0       /* Loader's lr */