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authorGraeme Russ <graeme.russ@gmail.com>2011-12-19 14:26:18 +1100
committerGraeme Russ <graeme.russ@gmail.com>2012-01-04 22:29:40 +1100
commit58c7a6751dd0978172741503b4dc0c6b23a60b33 (patch)
treeab4730c79a8c522afc5c5ba02343aa2bb1e33f61 /arch/x86
parent98f1fa9fd4f468c67b5f4d16077898992d6bae0b (diff)
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x86: Tweak IDT and GDT for alignment and readability
-- Changes for v2: - Renamed to better reflect nature of changes
Diffstat (limited to 'arch/x86')
-rw-r--r--arch/x86/cpu/interrupts.c2
-rw-r--r--arch/x86/cpu/start16.S57
2 files changed, 46 insertions, 13 deletions
diff --git a/arch/x86/cpu/interrupts.c b/arch/x86/cpu/interrupts.c
index e0958eb..43ec3f8 100644
--- a/arch/x86/cpu/interrupts.c
+++ b/arch/x86/cpu/interrupts.c
@@ -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;
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 */