43 lines
1.4 KiB
ArmAsm
43 lines
1.4 KiB
ArmAsm
; Copyright 2022 Mattia Giambirtone & Contributors
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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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; Utilities to switch to protected mode and load our GDT
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[bits 16]
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switch_to_protected_mode:
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cli ; Now we disable interrupts
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lgdt [gdt_descriptor] ; Time to load the GDT descriptor
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; We set 32-bit mode in CR0. Almost done!
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mov eax, cr0
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or eax, 0x1
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mov cr0, eax
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jmp CODE_SEG:switch32 ; At last, we perform a far jump into a different segment
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[bits 32]
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switch32: ; We're not in 32 bit mode, yay!
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mov ax, DATA_SEG ; Time to update the segment registers with their new values
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mov ds, ax
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mov ss, ax
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mov es, ax
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; Bonus: we have two more user-defined
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; segment registers when in 32-bit mode
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mov fs, ax
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mov gs, ax
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mov ebp, 0x1f8400 ; We also make the stack larger (2MiB)
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mov esp, ebp
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call BEGIN_32BIT ; We call back into mbr.s which loads the kernel
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