Kieron Morris
64b3c9a7ba
Added the apache license to all source files, accounting for authors. Also added a license.md containing the apache license + contributors.md listing all contributors.
122 lines
3.3 KiB
ObjectPascal
122 lines
3.3 KiB
ObjectPascal
// Copyright 2021 Kieron Morris
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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{
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Global Descriptor Table - Data Structures & Interface.
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@author(Kieron Morris <kjm@kieronmorris.me>)
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}
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unit gdt;
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interface
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uses
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console;
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type
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TGDT_Entry = packed record
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limit_low : uint16;
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base_low : uint16;
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base_middle : uint8;
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access : uint8;
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granularity : uint8;
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base_high : uint8;
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end;
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PGDT_Entry = ^TGDT_Entry;
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TGDT_Pointer = packed record
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limit : uint16;
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base : uint32;
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end;
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var
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gdt_entries : array[0..1023] of TGDT_Entry;
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gdt_pointer : TGDT_Pointer;
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procedure init();
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procedure set_gate(Gate_Number : uint32; Base : uint32; Limit : uint32; Access : uint8; Granularity : uint8);
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procedure flush;
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procedure reload;
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implementation
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procedure flush_gdt(gdt_pointer : uint32); assembler; nostackframe;
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asm
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MOV EAX, gdt_pointer
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LGDT [EAX]
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MOV AX, $10
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MOV DS, AX
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MOV ES, AX
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MOV FS, AX
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MOV GS, AX
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MOV SS, AX
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db $EA // Bypass stupid inline ASM restrictions-
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dw @@flush, $08 // by assembling the farjump instruction ourselves.
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@@flush: // It's just data, honest gov'.
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end;
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procedure flush;
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begin
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console.outputln('GDT','FLUSH.');
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flush_gdt(uint32(@gdt_pointer));
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end;
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procedure reload_gdt(gdt_ptr : uint32); assembler;
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asm
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MOV EAX, gdt_ptr
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LGDT [EAX]
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end;
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procedure reload;
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begin
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console.outputln('GDT','RELOAD.');
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reload_gdt(uint32(@gdt_pointer));
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end;
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procedure set_gate(Gate_Number : uint32; Base : uint32; Limit : uint32; Access : uint8; Granularity : uint8);
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var
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lLimit : uint32;
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begin
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lLimit:= (Gate_Number + 1) * 8;
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lLimit:= lLimit - 1;
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if lLimit > gdt_pointer.limit then begin
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gdt_pointer.limit:= lLimit;
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end;
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gdt_entries[Gate_Number].base_low := (Base AND $FFFF);
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gdt_entries[Gate_Number].base_middle := (Base SHR 16) AND $FF;
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gdt_entries[Gate_Number].base_high := (Base SHR 24) AND $FF;
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gdt_entries[Gate_Number].limit_low := (Limit AND $FFFF);
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gdt_entries[Gate_Number].granularity := ((Limit SHR 16) AND $0F) OR (Granularity AND $F0);
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gdt_entries[Gate_Number].access := Access;
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console.output('GDT','GATE ');
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console.writeint(Gate_Number);
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console.writestringln(' SET.');
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end;
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procedure init();
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begin
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console.outputln('GDT','INIT START.');
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gdt_pointer.limit:= 0;
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gdt_pointer.base := uint32(@gdt_entries);
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set_gate($00, $00, $00, $00, $00); //OFFSET: 0
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set_gate($01, $00, $FFFFFFFF, $9A, $CF); //OFFSET: 8
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set_gate($02, $00, $FFFFFFFF, $92, $CF); //OFFSET: 16
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set_gate($03, $00, $FFFFFFFF, $FA, $CF); //OFFSET: 24
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set_gate($04, $00, $FFFFFFFF, $F2, $CF); //OFFSET: 32
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flush;
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console.outputln('GDT','INIT END.');
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end;
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end. |