diff options
| author | Marvin Borner | 2020-07-22 00:24:54 +0200 |
|---|---|---|
| committer | Marvin Borner | 2020-07-22 00:24:54 +0200 |
| commit | a06e4d3a2e0c00210b54f5c060e90c8e5b425646 (patch) | |
| tree | bf51f3a563c96b37eb39a955a571f9de12e5959e | |
| parent | 08a790ffd8d9754a84c0d1ce4e8330f4617333dd (diff) | |
Removed some magic gdt numbers
| -rw-r--r-- | src/entry.asm | 20 |
1 files changed, 14 insertions, 6 deletions
diff --git a/src/entry.asm b/src/entry.asm index 11c3f71..487e4b4 100644 --- a/src/entry.asm +++ b/src/entry.asm @@ -50,6 +50,14 @@ %define A20_ENABLED 0b10 ; Bit 1 defines whether A20 is enabled %define A20_EXCLUDE_BIT 0xfe ; Bit 0 may be write-only, causing a crash +; GDT constants (bitmap) +%define GDT_MAX_LIMIT 0xffff +%define GDT_PRESENT 0b10000000 ; Is present +%define GDT_DESCRIPTOR 0b00010000 ; Descriptor type, set for code/data +%define GDT_EXECUTABLE 0b00001000 ; Can be executed +%define GDT_READWRITE 0b00000010 ; Read/write access for code/data +%define GDT_GRANULARITY (0xc0 | 0x0f) ; Use paged 32 granularity + ; Kernel constants %define STACK_POINTER 0x00900000 ; The initial stack pointer in kernel mode %define KERNEL_POSITION 0x00050000 ; Loaded kernel position in protected mode (* 0x10) @@ -328,18 +336,18 @@ gdt_null: ; Must be null dd 0 dd 0 gdt_code: ; Code section - dw 0xFFFF ; Limit + dw GDT_MAX_LIMIT ; Limit dw 0 ; First base db 0 ; Second base - db 0x9A ; Configuration - db 0xCF ; Granularity + db (GDT_PRESENT | GDT_DESCRIPTOR | GDT_EXECUTABLE | GDT_READWRITE) ; Configuration + db GDT_GRANULARITY ; Granularity db 0 ; Third base gdt_data: ; Data section - dw 0xFFFF ; Limit + dw GDT_MAX_LIMIT ; Limit dw 0 ; First base db 0 ; Second base - db 0x92 ; Configuration - db 0xCF ; Granularity + db (GDT_PRESENT | GDT_DESCRIPTOR | GDT_READWRITE) ; Configuration + db GDT_GRANULARITY ; Granularity db 0 ; Third base gdt_end: gdt_desc: |