The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/amd64/amd64/mpboot.S

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    1 /*-
    2  * Copyright (c) 2003 Peter Wemm
    3  * All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  *
   14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   24  * SUCH DAMAGE.
   25  *
   26  * $FreeBSD: releng/6.3/sys/amd64/amd64/mpboot.S 173886 2007-11-24 19:45:58Z cvs2svn $
   27  */
   28 
   29 #include <machine/asmacros.h>           /* miscellaneous asm macros */
   30 #include <machine/specialreg.h>
   31 
   32 #include "assym.s"
   33 
   34         .data                           /* So we can modify it */
   35 
   36         .p2align 4,0
   37         .globl  mptramp_start
   38 mptramp_start:
   39         .code16
   40         /*
   41          * The AP enters here in response to the startup IPI.
   42          * We are in real mode. %cs is the only segment register set.
   43          */
   44         cli                             /* make sure no interrupts */
   45         mov     %cs, %ax                /* copy %cs to %ds.  Remember these */
   46         mov     %ax, %ds                /* are offsets rather than selectors */
   47         mov     %ax, %ss
   48 
   49         /*
   50          * Find relocation base and patch the gdt descript and ljmp targets
   51          */
   52         xorl    %ebx,%ebx
   53         mov     %cs, %bx
   54         sall    $4, %ebx                /* %ebx is now our relocation base */
   55         orl     %ebx, lgdt_desc-mptramp_start+2
   56         orl     %ebx, jmp_32-mptramp_start+2
   57         orl     %ebx, jmp_64-mptramp_start+1
   58 
   59         /*
   60          * Load the descriptor table pointer.  We'll need it when running
   61          * in 16 bit protected mode.
   62          */
   63         lgdt    lgdt_desc-mptramp_start
   64 
   65         /* Enable protected mode */
   66         movl    $CR0_PE, %eax
   67         mov     %eax, %cr0 
   68 
   69         /*
   70          * Now execute a far jump to turn on protected mode.  This
   71          * causes the segment registers to turn into selectors and causes
   72          * %cs to be loaded from the gdt.
   73          *
   74          * The following instruction is:
   75          * ljmpl $bootcode-gdt, $protmode-mptramp_start
   76          * but gas cannot assemble that.  And besides, we patch the targets
   77          * in early startup and its a little clearer what we are patching.
   78          */
   79 jmp_32:
   80         .byte   0x66                    /* size override to 32 bits */
   81         .byte   0xea                    /* opcode for far jump */
   82         .long   protmode-mptramp_start  /* offset in segment */
   83         .word   bootcode-gdt            /* index in gdt for 32 bit code */
   84 
   85         /*
   86          * At this point, we are running in 32 bit legacy protected mode.
   87          */
   88         .code32
   89 protmode:
   90         mov     $bootdata-gdt, %eax
   91         mov     %ax, %ds
   92 
   93         /* Turn on the PAE, PSE and PGE bits for when paging is enabled */
   94         mov     %cr4, %eax
   95         orl     $(CR4_PAE | CR4_PSE), %eax
   96         mov     %eax, %cr4
   97 
   98         /*
   99          * Enable EFER.LME so that we get long mode when all the prereqs are
  100          * in place.  In this case, it turns on when CR0_PG is finally enabled.
  101          * Pick up a few other EFER bits that we'll use need we're here.
  102          */
  103         movl    $MSR_EFER, %ecx
  104         rdmsr
  105         orl     $EFER_LME | EFER_SCE, %eax
  106         wrmsr
  107 
  108         /*
  109          * Point to the embedded page tables for startup.  Note that this
  110          * only gets accessed after we're actually in 64 bit mode, however
  111          * we can only set the bottom 32 bits of %cr3 in this state.  This
  112          * means we are required to use a temporary page table that is below
  113          * the 4GB limit.  %ebx is still our relocation base.  We could just
  114          * subtract 3 * PAGE_SIZE, but that would be too easy.
  115          */
  116         leal    mptramp_pagetables-mptramp_start(%ebx),%eax
  117         movl    (%eax), %eax
  118         mov     %eax, %cr3
  119 
  120         /*
  121          * Finally, switch to long bit mode by enabling paging.  We have
  122          * to be very careful here because all the segmentation disappears
  123          * out from underneath us.  The spec says we can depend on the
  124          * subsequent pipelined branch to execute, but *only if* everthing
  125          * is still identity mapped.  If any mappings change, the pipeline
  126          * will flush.
  127          */
  128         mov     %cr0, %eax
  129         orl     $CR0_PG, %eax
  130         mov     %eax, %cr0
  131 
  132         /*
  133          * At this point paging is enabled, and we are in "compatability" mode.
  134          * We do another far jump to reload %cs with the 64 bit selector.
  135          * %cr3 points to a 4-level page table page.
  136          * We cannot yet jump all the way to the kernel because we can only
  137          * specify a 32 bit linear address.  So, yet another trampoline.
  138          *
  139          * The following instruction is:
  140          * ljmp $kernelcode-gdt, $tramp_64-mptramp_start
  141          * but gas cannot assemble that.  And besides, we patch the targets
  142          * in early startup and its a little clearer what we are patching.
  143          */
  144 jmp_64:
  145         .byte   0xea                    /* opcode for far jump */
  146         .long   tramp_64-mptramp_start  /* offset in segment */
  147         .word   kernelcode-gdt          /* index in gdt for 64 bit code */
  148 
  149         /*
  150          * Yeehar!  We're running in 64 bit mode!  We can mostly ignore our
  151          * segment registers, and get on with it.
  152          * Note that we are running at the correct virtual address, but with
  153          * a 1:1 1GB mirrored mapping over entire address space.  We had better
  154          * switch to a real %cr3 promptly so that we can get to the direct map
  155          * space. Remember that jmp is relative and that we've been relocated,
  156          * so use an indirect jump.
  157          */
  158         .code64
  159 tramp_64:
  160         movabsq $entry_64,%rax          /* 64 bit immediate load */
  161         jmp     *%rax
  162 
  163         .p2align 4,0
  164 gdt:
  165         /*
  166          * All segment descriptor tables start with a null descriptor
  167          */
  168         .long   0x00000000
  169         .long   0x00000000
  170 
  171         /*
  172          * This is the 64 bit long mode code descriptor.  There is no
  173          * 64 bit data descriptor.
  174          */
  175 kernelcode:
  176         .long   0x00000000
  177         .long   0x00209800
  178 
  179         /*
  180          * This is the descriptor for the 32 bit boot code.
  181          * %cs:  +A, +R, -C, DPL=0, +P, +D, +G
  182          * Accessed, Readable, Present, 32 bit, 4G granularity
  183          */
  184 bootcode:
  185         .long   0x0000ffff
  186         .long   0x00cf9b00
  187 
  188         /*
  189          * This is the descriptor for the 32 bit boot data.
  190          * We load it into %ds and %ss.  The bits for each selector
  191          * are interpreted slightly differently.
  192          * %ds:  +A, +W, -E, DPL=0, +P, +D, +G
  193          * %ss:  +A, +W, -E, DPL=0, +P, +B, +G
  194          * Accessed, Writeable, Expand up, Present, 32 bit, 4GB 
  195          * For %ds, +D means 'default operand size is 32 bit'.
  196          * For %ss, +B means the stack register is %esp rather than %sp.
  197          */
  198 bootdata:
  199         .long   0x0000ffff
  200         .long   0x00cf9300
  201 
  202 gdtend:
  203 
  204         /*
  205          * The address of our page table pages that the boot code
  206          * uses to trampoline up to kernel address space.
  207          */
  208         .globl  mptramp_pagetables
  209 mptramp_pagetables:
  210         .long   0
  211 
  212         /*
  213          * The pseudo descriptor for lgdt to use.
  214          */
  215 lgdt_desc:      
  216         .word   gdtend-gdt              /* Length */
  217         .long   gdt-mptramp_start       /* Offset plus %ds << 4 */
  218 
  219         .globl  mptramp_end
  220 mptramp_end:
  221 
  222         /*
  223          * From here on down is executed in the kernel .text section.
  224          *
  225          * Load a real %cr3 that has all the direct map stuff and switches
  226          * off the 1GB replicated mirror.  Load a stack pointer and jump
  227          * into AP startup code in C.
  228          */
  229         .text
  230         .code64
  231         .p2align 4,0
  232 entry_64:
  233         movq    KPML4phys, %rax
  234         movq    %rax, %cr3
  235         movq    bootSTK, %rsp
  236         jmp     init_secondary

Cache object: 71001b0242224caeafd90729ccbfc24a


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