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| author | kaashoek <kaashoek> | 2006-06-22 01:28:57 +0000 |
|---|---|---|
| committer | kaashoek <kaashoek> | 2006-06-22 01:28:57 +0000 |
| commit | 21a88fd487177841c882d9017bd9f4476801c6f6 (patch) | |
| tree | bfa061e00662efde2186d6c0498fc78f889356ce /bootother.S | |
| parent | 7baa34a421e4c970ee90c2537ceacd7230f2474e (diff) | |
| download | xv6-labs-21a88fd487177841c882d9017bd9f4476801c6f6.tar.gz xv6-labs-21a88fd487177841c882d9017bd9f4476801c6f6.tar.bz2 xv6-labs-21a88fd487177841c882d9017bd9f4476801c6f6.zip | |
checkpoint. booting second processor. stack is messed up, but thanks to cliff
and plan 9 code, at least boots and gets into C code.
Diffstat (limited to 'bootother.S')
| -rw-r--r-- | bootother.S | 77 |
1 files changed, 77 insertions, 0 deletions
diff --git a/bootother.S b/bootother.S new file mode 100644 index 0000000..cba4a5f --- /dev/null +++ b/bootother.S @@ -0,0 +1,77 @@ +#include "asm.h" + +/* + * Start an Application Processor. This must be placed on a 4KB boundary + * somewhere in the 1st MB of conventional memory (APBOOTSTRAP). However, + * due to some shortcuts below it's restricted further to within the 1st + * 64KB. The AP starts in real-mode, with + * CS selector set to the startup memory address/16; + * CS base set to startup memory address; + * CS limit set to 64KB; + * CPL and IP set to 0. + * + * Credit: Cliff Frey + */ + +.set PROT_MODE_CSEG,0x8 # code segment selector +.set PROT_MODE_DSEG,0x10 # data segment selector +.set CR0_PE_ON,0x1 # protected mode enable flag + +.globl start +start: .code16 # This runs in real mode + cli # Disable interrupts + cld # String operations increment + + # Set up the important data segment registers (DS, ES, SS). + xorw %ax,%ax # Segment number zero + movw %ax,%ds # -> Data Segment + movw %ax,%es # -> Extra Segment + movw %ax,%ss # -> Stack Segment + + # Set up the stack pointer, growing downward from 0x7000. + movw $start,%sp # Stack Pointer + +#### Switch from real to protected mode +#### The descriptors in our GDT allow all physical memory to be accessed. +#### Furthermore, the descriptors have base addresses of 0, so that the +#### segment translation is a NOP, ie. virtual addresses are identical to +#### their physical addresses. With this setup, immediately after +#### enabling protected mode it will still appear to this code +#### that it is running directly on physical memory with no translation. +#### This initial NOP-translation setup is required by the processor +#### to ensure that the transition to protected mode occurs smoothly. + + lgdt gdtdesc # load GDT -- mandatory in protected mode + movl %cr0, %eax # turn on protected mode + orl $CR0_PE_ON, %eax # + movl %eax, %cr0 # + ### CPU magic: jump to relocation, flush prefetch queue, and reload %cs + ### Has the effect of just jmp to the next instruction, but simultaneous + ### loads CS with $PROT_MODE_CSEG. + ljmp $PROT_MODE_CSEG, $protcseg + +#### we are in 32-bit protected mode (hence the .code32) +.code32 +protcseg: + # Set up the protected-mode data segment registers + movw $PROT_MODE_DSEG, %ax # Our data segment selector + movw %ax, %ds # -> DS: Data Segment + movw %ax, %es # -> ES: Extra Segment + movw %ax, %fs # -> FS + movw %ax, %gs # -> GS + movw %ax, %ss # -> SS: Stack Segment + + # XXX hack + movl 0x10018, %eax # elfhdr->entry (left over in scratch space) + # subl $KERNBASE, %eax + jmp *%eax # this jumps to _start in kern/entry.S + +.p2align 2 # force 4 byte alignment +gdt: + SEG_NULL # null seg + SEG(STA_X|STA_R, 0x0, 0xffffffff) # code seg + SEG(STA_W, 0x0, 0xffffffff) # data seg + +gdtdesc: + .word 0x17 # sizeof(gdt) - 1 + .long gdt # address gdt |