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Annotation of qemu/pc-bios/optionrom/linuxboot.S, revision 1.1

1.1     ! root        1: /*
        !             2:  * Linux Boot Option ROM
        !             3:  *
        !             4:  * This program is free software; you can redistribute it and/or modify
        !             5:  * it under the terms of the GNU General Public License as published by
        !             6:  * the Free Software Foundation; either version 2 of the License, or
        !             7:  * (at your option) any later version.
        !             8:  *
        !             9:  * This program is distributed in the hope that it will be useful,
        !            10:  * but WITHOUT ANY WARRANTY; without even the implied warranty of
        !            11:  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
        !            12:  * GNU General Public License for more details.
        !            13:  *
        !            14:  * You should have received a copy of the GNU General Public License
        !            15:  * along with this program; if not, see <http://www.gnu.org/licenses/>.
        !            16:  *
        !            17:  * Copyright Novell Inc, 2009
        !            18:  *   Authors: Alexander Graf <[email protected]>
        !            19:  *
        !            20:  * Based on code in hw/pc.c.
        !            21:  */
        !            22: 
        !            23: #include "optionrom.h"
        !            24: 
        !            25: BOOT_ROM_START
        !            26: 
        !            27: run_linuxboot:
        !            28: 
        !            29:        cli
        !            30:        cld
        !            31: 
        !            32:        jmp             copy_kernel
        !            33: boot_kernel:
        !            34: 
        !            35:        read_fw         FW_CFG_SETUP_ADDR
        !            36: 
        !            37:        mov             %eax, %ebx
        !            38:        shr             $4, %ebx
        !            39: 
        !            40:        /* All segments contain real_addr */
        !            41:        mov             %bx, %ds
        !            42:        mov             %bx, %es
        !            43:        mov             %bx, %fs
        !            44:        mov             %bx, %gs
        !            45:        mov             %bx, %ss
        !            46: 
        !            47:        /* CX = CS we want to jump to */
        !            48:        add             $0x20, %bx
        !            49:        mov             %bx, %cx
        !            50: 
        !            51:        /* SP = cmdline_addr-real_addr-16 */
        !            52:        read_fw         FW_CFG_CMDLINE_ADDR
        !            53:        mov             %eax, %ebx
        !            54:        read_fw         FW_CFG_SETUP_ADDR
        !            55:        sub             %eax, %ebx
        !            56:        sub             $16, %ebx
        !            57:        mov             %ebx, %esp
        !            58: 
        !            59:        /* Build indirect lret descriptor */
        !            60:        pushw           %cx             /* CS */
        !            61:        xor             %ax, %ax
        !            62:        pushw           %ax             /* IP = 0 */
        !            63: 
        !            64:        /* Clear registers */
        !            65:        xor             %eax, %eax
        !            66:        xor             %ebx, %ebx
        !            67:        xor             %ecx, %ecx
        !            68:        xor             %edx, %edx
        !            69:        xor             %edi, %edi
        !            70:        xor             %ebp, %ebp
        !            71: 
        !            72:        /* Jump to Linux */
        !            73:        lret
        !            74: 
        !            75: 
        !            76: copy_kernel:
        !            77: 
        !            78:        /* We need to load the kernel into memory we can't access in 16 bit
        !            79:           mode, so let's get into 32 bit mode, write the kernel and jump
        !            80:           back again. */
        !            81: 
        !            82:        /* Reserve space on the stack for our GDT descriptor. */
        !            83:        mov             %esp, %ebp
        !            84:        sub             $16, %esp
        !            85: 
        !            86:        /* Now create the GDT descriptor */
        !            87:        movw            $((3 * 8) - 1), -16(%bp)
        !            88:        mov             %cs, %eax
        !            89:        shl             $4, %eax
        !            90:        addl            $gdt, %ebx
        !            91:        movl            %ebx, -14(%bp)
        !            92: 
        !            93:        /* And load the GDT */
        !            94:        data32 lgdt     -16(%bp)
        !            95:        mov             %ebp, %esp
        !            96: 
        !            97:        /* Get us to protected mode now */
        !            98:        mov             $1, %eax
        !            99:        mov             %eax, %cr0
        !           100: 
        !           101:        /* So we can set ES to a 32-bit segment */
        !           102:        mov             $0x10, %eax
        !           103:        mov             %eax, %es
        !           104: 
        !           105:        /* We're now running in 16-bit CS, but 32-bit ES! */
        !           106: 
        !           107:        /* Load kernel and initrd */
        !           108:        read_fw_blob(FW_CFG_KERNEL)
        !           109:        read_fw_blob(FW_CFG_INITRD)
        !           110:        read_fw_blob(FW_CFG_CMDLINE)
        !           111:        read_fw_blob(FW_CFG_SETUP)
        !           112: 
        !           113:        /* And now jump into Linux! */
        !           114:        mov             $0, %eax
        !           115:        mov             %eax, %cr0
        !           116: 
        !           117:        /* ES = CS */
        !           118:        mov             %cs, %ax
        !           119:        mov             %ax, %es
        !           120: 
        !           121:        jmp             boot_kernel
        !           122: 
        !           123: /* Variables */
        !           124: 
        !           125: .align 4, 0
        !           126: gdt:
        !           127:        /* 0x00 */
        !           128: .byte  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
        !           129: 
        !           130:        /* 0x08: code segment (base=0, limit=0xfffff, type=32bit code exec/read, DPL=0, 4k) */
        !           131: .byte  0xff, 0xff, 0x00, 0x00, 0x00, 0x9a, 0xcf, 0x00
        !           132: 
        !           133:        /* 0x10: data segment (base=0, limit=0xfffff, type=32bit data read/write, DPL=0, 4k) */
        !           134: .byte  0xff, 0xff, 0x00, 0x00, 0x00, 0x92, 0xcf, 0x00
        !           135: 
        !           136: BOOT_ROM_END

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