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x86: Tweak IDT and GDT for alignment and readability 

--
Changes for v2:
 - Renamed to better reflect nature of changes
This commit is contained in:
Graeme Russ 2011-12-19 14:26:18 +11:00
parent 98f1fa9fd4
commit 58c7a6751d
2 changed files with 46 additions and 13 deletions
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2
arch/x86/cpu/interrupts.c
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@ -174,7 +174,7 @@ struct desc_ptr {
unsigned short segment;
} __packed;
struct idt_entry idt[256] __attribute__((aligned(16)));
struct idt_entry idt[256] __aligned(16);
struct desc_ptr idt_ptr;

57
arch/x86/cpu/start16.S
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@ -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 */