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| author | Graeme Russ <graeme.russ@gmail.com> | 2011-12-19 03:26:18 (GMT) |
|---|---|---|
| committer | Graeme Russ <graeme.russ@gmail.com> | 2012-01-04 11:29:40 (GMT) |
| commit | 58c7a6751dd0978172741503b4dc0c6b23a60b33 (patch) | |
| tree | ab4730c79a8c522afc5c5ba02343aa2bb1e33f61 /arch/x86/cpu/start16.S | |
| parent | 98f1fa9fd4f468c67b5f4d16077898992d6bae0b (diff) | |
| download | u-boot-fsl-qoriq-58c7a6751dd0978172741503b4dc0c6b23a60b33.tar.xz | |
x86: Tweak IDT and GDT for alignment and readability
--
Changes for v2:
- Renamed to better reflect nature of changes
Diffstat (limited to 'arch/x86/cpu/start16.S')
| -rw-r--r-- | arch/x86/cpu/start16.S | 57 |
1 files changed, 45 insertions, 12 deletions
diff --git a/arch/x86/cpu/start16.S b/arch/x86/cpu/start16.S index 33e53cd..cc393ff 100644 --- a/arch/x86/cpu/start16.S +++ b/arch/x86/cpu/start16.S @@ -86,7 +86,11 @@ gdt_ptr: .word 0x20 /* limit (32 bytes = 4 GDT entries) */ .long BOOT_SEG + gdt /* base */ - /* The GDT table ... +/* Some CPUs are picky about GDT alignment... */ +.align 16 +gdt: + /* + * The GDT table ... * * Selector Type * 0x00 NULL @@ -94,17 +98,46 @@ gdt_ptr: * 0x10 32bit code * 0x18 32bit data/stack */ + /* The NULL Desciptor - Mandatory */ + .word 0x0000 /* limit_low */ + .word 0x0000 /* base_low */ + .byte 0x00 /* base_middle */ + .byte 0x00 /* access */ + .byte 0x00 /* flags + limit_high */ + .byte 0x00 /* base_high */ -gdt: - .word 0, 0, 0, 0 /* NULL */ - .word 0, 0, 0, 0 /* unused */ + /* Unused Desciptor - (matches Linux) */ + .word 0x0000 /* limit_low */ + .word 0x0000 /* base_low */ + .byte 0x00 /* base_middle */ + .byte 0x00 /* access */ + .byte 0x00 /* flags + limit_high */ + .byte 0x00 /* base_high */ - .word 0xFFFF /* 4Gb - (0x100000*0x1000 = 4Gb) */ - .word 0 /* base address = 0 */ - .word 0x9B00 /* code read/exec */ - .word 0x00CF /* granularity = 4096, 386 (+5th nibble of limit) */ + /* + * The Code Segment Descriptor: + * - Base = 0x00000000 + * - Size = 4GB + * - Access = Present, Ring 0, Exec (Code), Readable + * - Flags = 4kB Granularity, 32-bit + */ + .word 0xffff /* limit_low */ + .word 0x0000 /* base_low */ + .byte 0x00 /* base_middle */ + .byte 0x9b /* access */ + .byte 0xcf /* flags + limit_high */ + .byte 0x00 /* base_high */ - .word 0xFFFF /* 4Gb - (0x100000*0x1000 = 4Gb) */ - .word 0x0 /* base address = 0 */ - .word 0x9300 /* data read/write */ - .word 0x00CF /* granularity = 4096, 386 (+5th nibble of limit) */ + /* + * The Data Segment Descriptor: + * - Base = 0x00000000 + * - Size = 4GB + * - Access = Present, Ring 0, Non-Exec (Data), Writable + * - Flags = 4kB Granularity, 32-bit + */ + .word 0xffff /* limit_low */ + .word 0x0000 /* base_low */ + .byte 0x00 /* base_middle */ + .byte 0x93 /* access */ + .byte 0xcf /* flags + limit_high */ + .byte 0x00 /* base_high */ |