Fixed 32-bit protected-mode test code
This commit is contained in:
Jeff Parsons
jeffpar
parent
f36b79cd25
commit
9ab1f92adc
5 changed files with 115 additions and 81 deletions
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@ -21,6 +21,7 @@ ACC_TYPE_WRITABLE equ 0x0200
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ACC_TYPE_CODE_READABLE equ (0x1a00 | ACC_PRESENT)
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ACC_TYPE_DATA_WRITABLE equ (0x1200 | ACC_PRESENT)
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EXT_NONE equ 0x0000
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EXT_BIG equ 0x0040
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;
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@ -33,7 +34,7 @@ EXT_BIG equ 0x0040
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; 0x0d08-0x0d0f GDTR
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; 0x0d10-0x0fff reserved
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;
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; And in the second page (0x1000-0x1fff), let's build a page directory, followed by a single page table that
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; And in the second page (0x1000-0x1fff), we build a page directory, followed by a single page table that
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; will allow us to map up to 4Mb (although we'll only create entries for the first 1Mb).
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;
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RAM_GDT equ 0x0c00
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@ -50,8 +51,12 @@ CR0_MSW_PE equ 0x0001
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; set initializes a register to the specified value (eg, "set eax,0")
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;
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%macro set 2
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%if %2 = 0
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sub %1,%1
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%ifnum %2
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%if %2 = 0
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xor %1,%1
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%else
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mov %1,%2
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%endif
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%else
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mov %1,%2
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%endif
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@ -60,7 +65,7 @@ CR0_MSW_PE equ 0x0001
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;
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; defDesc defines a descriptor, given a base (%1), limit (%2), type (%3), dpl (%4), and ext (%5)
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;
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%macro defDesc 1-4 0,0,0,0
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%macro defDesc 1-5 0,0,0,0,0
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dw (%2 & 0x0000ffff)
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dw (%1 & 0x0000ffff)
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dw ((%1 & 0x00ff0000) >> 16) | %3 | (%4 << 13)
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@ -68,15 +73,16 @@ CR0_MSW_PE equ 0x0001
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%endmacro
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;
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; setDesc creates a descriptor, given a base (%1), limit (%2), type (%3), dpl (%4), and ext (%5)
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; setDesc creates a descriptor, given a base (%1), limit (%2), type (%3), ext (%4), and selector (%5)
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;
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%assign selDesc 0
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%macro setDesc 1-4 0,0,0,none
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%macro setDesc 1-5 0,0,0,0,none
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set ebx,%1
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set ecx,%2
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set edx,%3
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set dx,%3
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set ax,%4
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call storeDesc
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%assign %4 selDesc
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%assign %5 selDesc
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%assign selDesc selDesc+8
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%endmacro
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@ -99,11 +105,13 @@ start: cli ; disable all interrupts
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cmp eax,ebx
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je near initRAM ; apparently we have to tell NASM "near" because this is a forward reference
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times 32768 nop ; lots of NOPs to force a 16-bit conditional jump
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;
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; storeDesc(EBX=base, ECX=limit, EDX=type, EDI=target)
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; storeDesc(EBX=base, ECX=limit, DX=type, AX=ext, DI=address of descriptor)
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;
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storeDesc:
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cld
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push ax
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mov ax,cx
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stosw ; store the low 16 bits of limit from ECX
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mov ax,bx
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@ -112,13 +120,17 @@ storeDesc:
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shr ebx,16
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mov al,bl
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stosw
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pop ax
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shr ecx,16
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mov al,cl
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and al,0xf
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and cl,0xf
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or al,cl
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mov ah,bh
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stosw
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ret
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;
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; The following ROM-based data structures are obsolete, because we build these data structures in RAM now.
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;
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addrGDT:dw romGDTEnd - romGDT - 1 ; 16-bit limit of romGDT
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dw romGDT, 0xffff ; 32-bit base address of romGDT (works as long as we're aliased at 0xffff0000)
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@ -126,13 +138,18 @@ romGDT: defDesc 0 ; the first descriptor in any descriptor table is always a d
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defDesc 0x000f0000,0x0000ffff,ACC_TYPE_CODE_READABLE
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defDesc 0x00000000,0x000fffff,ACC_TYPE_DATA_WRITABLE
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romGDTEnd:
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;
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; End of ROM-based data structures
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;
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initRAM:
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set edi,RAM_GDT
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mov [RAM_GDTR+2],edi
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setDesc 0,0,0,NULL
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setDesc 0x000f0000,0x0000ffff,ACC_TYPE_CODE_READABLE,CSEG_PROT
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setDesc 0x00000000,0x000fffff,ACC_TYPE_DATA_WRITABLE,DSEG_PROT
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setDesc 0,0,0,0,NULL
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mov eax,cs
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shl eax,4
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setDesc eax,0x0000ffff,ACC_TYPE_CODE_READABLE,EXT_BIG,CSEG_PROT
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setDesc 0x0,0x000fffff,ACC_TYPE_DATA_WRITABLE,EXT_BIG,DSEG_PROT
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sub edi,RAM_GDT
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dec edi
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mov [RAM_GDTR],di
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@ -141,20 +158,25 @@ goProt: o32 lgdt [RAM_GDTR]
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mov eax,cr0
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or eax,CR0_MSW_PE
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mov cr0,eax
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jmp dword CSEG_PROT:inProt
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inProt: mov ax,DSEG_PROT
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jmp CSEG_PROT:inProt
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inProt:
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bits 32
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mov ax,DSEG_PROT
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mov ds,ax
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mov es,ax
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mov ss,ax
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;
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; Do some protected-mode tests...
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; Do some protected-mode tests now...
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;
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goReal: mov eax,cr0
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and eax,~CR0_MSW_PE
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mov cr0,eax
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jmp dword CSEG_REAL:inReal
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inReal: or eax,1
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bits 16
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jmp CSEG_REAL:inReal
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inReal:
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or ax,1
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jnz start ; apparently we do NOT have to say "near" here since this is a backward reference
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;
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@ -163,7 +185,6 @@ inReal: or eax,1
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;
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times 0xfff0-0x100-($-$$) nop
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bits 16
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jmp CSEG_REAL:start
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db 0x20
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