source: mainline/arch/ppc32/src/start.S@ 778c1e1

#
# Copyright (C) 2005 Jakub Jermar
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#include <arch/asm/regname.h>
#include <arch/asm/spr.h>

.section K_TEXT_START

.global kernel_image_start

.org 0x0
/* 256 bytes of some data */
/* exception table - must use 'ba' instructions for branches,
 * because it is elsewhere than the linker thinks
 */
.space 4096

kernel_image_start:
        /* Initialize OFW, might be needed before relocate_kernel? */
        lis r4, ofw@ha
        addi r4, r4, ofw@l
        stw r5, 0(r4)
        
        bl ofw_init
        bl preboot_read_config

        bl relocate_kernel
__after_reloc:
        /* Set stack to some more meaningful value */
        /* TODO: This is hardcoded for PearPC, must be changed later */
        lis r1, 0x70
        b main_bsp
        
relocate_kernel:
        /* TODO: We _know_ that pearpc loads it to 8MB, and
         * but it should be really generic
         */
        lis r4, 0x80 /* r4 is where data was loaded - 8MB */
        
        bl to_real_mode
        /* Now we are in real mode, copy first block and jump to it,
         * we are running in the loaded kernel now
         * We still have in r3 physical load kernel address
         */
        
        b __after_reloc /* We know in pearpc we are ok, so return,
                         * otherwise we should relocate kernel
                         * here
                         */

        

        
/* Turn off page translation
 * - assume that physical-loaded address is in r4
 */
to_real_mode:
        mflr r0
        
        lis   r5, ktext_start@ha // Expected start of kernel
        addi r5, r5, ktext_start@l
        
        add  r0, r4, r0         
        sub  r0, r0, r5         // r0 now contains physical return address
        
        mfmsr r3
        andis. r3, r3, (~MSR_DR | MSR_IR) >> 16
        mtspr SPRN_SRR0, r0
        mtspr SPRN_SRR1, r3
        sync                    // Really needed? RFI should do it as well?
        RFI