Linux has C macros and code to load the GTD after switching to Protected
Mode. Using these greatly simplifies the assembler code
Signed-off-by: Graeme Russ <graeme.russ at gmail.com>
---
arch/i386/cpu/cpu.c | 57 +++++++++++++++++++++++++++++
arch/i386/cpu/start.S | 96 -------------------------------------------------
2 files changed, 57 insertions(+), 96 deletions(-)
diff --git a/arch/i386/cpu/cpu.c b/arch/i386/cpu/cpu.c
index bd6aced..ae40384 100644
--- a/arch/i386/cpu/cpu.c
+++ b/arch/i386/cpu/cpu.c
@@ -37,6 +37,61 @@
#include <command.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)
{
/* initialize FPU, reset EM, set MP and NE */
@@ -51,6 +106,8 @@ int cpu_init_f(void)
int cpu_init_r(void)
{
+ reload_gdt();
+
/* Initialize core interrupt and exception functionality of CPU */
cpu_init_interrupts ();
return 0;
diff --git a/arch/i386/cpu/start.S b/arch/i386/cpu/start.S
index 7def8de..3cea04b 100644
--- a/arch/i386/cpu/start.S
+++ b/arch/i386/cpu/start.S
@@ -100,53 +100,6 @@ mem_init_ret:
jmp get_mem_size
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 */
movl $CONFIG_SYS_STACK_SIZE, %ecx
cmpl %ecx, %eax
@@ -221,52 +174,3 @@ die: hlt
blank_idt_ptr:
.word 0 /* limit */
.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:
--
1.7.1.422.g049e9