Djam/u-boot
1
0
Fork 0
mirror of https://github.com/u-boot/u-boot.git synced 2025-05-08 19:11:53 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions

x86: Move loading of GTD to C code

Browse source 
Linux has C macros and code to load the GTD after switching to Protected
Mode. Using these greatly simplifies the assembler code
This commit is contained in:
Graeme Russ 2010-10-07 20:03:21 +11:00
parent d664adb6bb
commit 59c6d0ef9a
2 changed files with 57 additions and 96 deletions
Download patch file Download diff file Expand all files Collapse all files

57
arch/i386/cpu/cpu.c
View file

@ -37,6 +37,61 @@
#include <command.h> #include <command.h>
#include <asm/interrupt.h> #include <asm/interrupt.h>
/* Constructor for a conventional segment GDT (or LDT) entry */
/* This is a macro so it can be used in initializers */
#define GDT_ENTRY(flags, base, limit) \
((((base) & 0xff000000ULL) << (56-24)) | \
(((flags) & 0x0000f0ffULL) << 40) | \
(((limit) & 0x000f0000ULL) << (48-16)) | \
(((base) & 0x00ffffffULL) << 16) | \
(((limit) & 0x0000ffffULL)))
/* Simple and small GDT entries for booting only */
#define GDT_ENTRY_32BIT_CS 2
#define GDT_ENTRY_32BIT_DS (GDT_ENTRY_32BIT_CS + 1)
#define GDT_ENTRY_16BIT_CS (GDT_ENTRY_32BIT_DS + 1)
#define GDT_ENTRY_16BIT_DS (GDT_ENTRY_16BIT_CS + 1)
/*
* Set up the GDT
*/
struct gdt_ptr {
u16 len;
u32 ptr;
} __attribute__((packed));
static void reload_gdt(void)
{
/* There are machines which are known to not boot with the GDT
being 8-byte unaligned. Intel recommends 16 byte alignment. */
static const u64 boot_gdt[] __attribute__((aligned(16))) = {
/* CS: code, read/execute, 4 GB, base 0 */
[GDT_ENTRY_32BIT_CS] = GDT_ENTRY(0xc09b, 0, 0xfffff),
/* DS: data, read/write, 4 GB, base 0 */
[GDT_ENTRY_32BIT_DS] = GDT_ENTRY(0xc093, 0, 0xfffff),
/* 16-bit CS: code, read/execute, 64 kB, base 0 */
[GDT_ENTRY_16BIT_CS] = GDT_ENTRY(0x109b, 0, 0x0ffff),
/* 16-bit DS: data, read/write, 64 kB, base 0 */
[GDT_ENTRY_16BIT_DS] = GDT_ENTRY(0x1093, 0, 0x0ffff),
};
static struct gdt_ptr gdt;
gdt.len = sizeof(boot_gdt)-1;
gdt.ptr = (u32)&boot_gdt;
asm volatile("lgdtl %0\n" \
"movl $((2+1)*8), %%ecx\n" \
"movl %%ecx, %%ds\n" \
"movl %%ecx, %%es\n" \
"movl %%ecx, %%fs\n" \
"movl %%ecx, %%gs\n" \
"movl %%ecx, %%ss" \
: : "m" (gdt) : "ecx");
}
int cpu_init_f(void) int cpu_init_f(void)
{ {
/* initialize FPU, reset EM, set MP and NE */ /* initialize FPU, reset EM, set MP and NE */
@ -51,6 +106,8 @@ int cpu_init_f(void)
int cpu_init_r(void) int cpu_init_r(void)
{ {
reload_gdt();
/* Initialize core interrupt and exception functionality of CPU */ /* Initialize core interrupt and exception functionality of CPU */
cpu_init_interrupts (); cpu_init_interrupts ();
return 0; return 0;

96
arch/i386/cpu/start.S
View file

@ -100,53 +100,6 @@ mem_init_ret:
jmp get_mem_size jmp get_mem_size
get_mem_size_ret: get_mem_size_ret:
/*
* We are now in 'Flat Protected Mode' and we know how much memory
* the board has. The (temporary) Global Descriptor Table is not
* in a 'Safe' place (it is either in Flash which can be erased or
* reprogrammed or in a fail-safe boot-strap image which could be
* over-written).
*
* Move the final gdt to a safe place (top of RAM) and load it.
* This is not a trivial excercise - the lgdt instruction does not
* have a register operand (memory only) and we may well be
* running from Flash, so self modifying code will not work here.
* To overcome this, we copy a stub into upper memory along with
* the GDT.
*/
/* Reduce upper memory limit by (Stub + GDT Pointer + GDT) */
subl $(end_gdt_setup - start_gdt_setup), %eax
/* Copy the GDT and Stub */
movl $start_gdt_setup, %esi
movl %eax, %edi
movl $(end_gdt_setup - start_gdt_setup), %ecx
shrl $2, %ecx
cld
rep movsl
/* write the lgdt 'parameter' */
subl $(jmp_instr - start_gdt_setup - 4), %ebp
addl %eax, %ebp
movl $(gdt_ptr - start_gdt_setup), %ebx
addl %eax, %ebx
movl %ebx, (%ebp)
/* write the gdt address into the pointer */
movl $(gdt_addr - start_gdt_setup), %ebp
addl %eax, %ebp
movl $(gdt - start_gdt_setup), %ebx
addl %eax, %ebx
movl %ebx, (%ebp)
/* Save the return address */
movl $load_gdt_ret, %ebp
/* Load the new (safe) Global Descriptor Table */
jmp *%eax
load_gdt_ret:
/* Check we have enough memory for stack */ /* Check we have enough memory for stack */
movl $CONFIG_SYS_STACK_SIZE, %ecx movl $CONFIG_SYS_STACK_SIZE, %ecx
cmpl %ecx, %eax cmpl %ecx, %eax
@ -221,52 +174,3 @@ die: hlt
blank_idt_ptr: blank_idt_ptr:
.word 0 /* limit */ .word 0 /* limit */
.long 0 /* base */ .long 0 /* base */
.align 4
start_gdt_setup:
lgdt gdt_ptr
jmp_instr:
jmp *%ebp
.align 4
gdt_ptr:
.word 0x30 /* limit (48 bytes = 6 GDT entries) */
gdt_addr:
.long gdt /* base */
/* The GDT table ...
*
* Selector Type
* 0x00 NULL
* 0x08 Unused
* 0x10 32bit code
* 0x18 32bit data/stack
* 0x20 16bit code
* 0x28 16bit data/stack
*/
.align 4
gdt:
.word 0, 0, 0, 0 /* NULL */
.word 0, 0, 0, 0 /* unused */
.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) */
.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) */
.word 0xFFFF /* 64kb */
.word 0 /* base address = 0 */
.word 0x9b00 /* data read/write */
.word 0x0010 /* granularity = 1 (+5th nibble of limit) */
.word 0xFFFF /* 64kb */
.word 0 /* base address = 0 */
.word 0x9300 /* data read/write */
.word 0x0010 /* granularity = 1 (+5th nibble of limit) */
end_gdt_setup: