x86: Move loading of GTD to C code
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
parent
d664adb6bb
commit
59c6d0ef9a
2 changed files with 57 additions and 96 deletions
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@ -37,6 +37,61 @@
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#include <command.h>
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#include <asm/interrupt.h>
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/* Constructor for a conventional segment GDT (or LDT) entry */
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/* This is a macro so it can be used in initializers */
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#define GDT_ENTRY(flags, base, limit) \
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((((base) & 0xff000000ULL) << (56-24)) | \
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(((flags) & 0x0000f0ffULL) << 40) | \
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(((limit) & 0x000f0000ULL) << (48-16)) | \
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(((base) & 0x00ffffffULL) << 16) | \
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(((limit) & 0x0000ffffULL)))
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/* Simple and small GDT entries for booting only */
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#define GDT_ENTRY_32BIT_CS 2
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#define GDT_ENTRY_32BIT_DS (GDT_ENTRY_32BIT_CS + 1)
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#define GDT_ENTRY_16BIT_CS (GDT_ENTRY_32BIT_DS + 1)
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#define GDT_ENTRY_16BIT_DS (GDT_ENTRY_16BIT_CS + 1)
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/*
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* Set up the GDT
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*/
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struct gdt_ptr {
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u16 len;
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u32 ptr;
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} __attribute__((packed));
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static void reload_gdt(void)
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{
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/* There are machines which are known to not boot with the GDT
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being 8-byte unaligned. Intel recommends 16 byte alignment. */
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static const u64 boot_gdt[] __attribute__((aligned(16))) = {
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/* CS: code, read/execute, 4 GB, base 0 */
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[GDT_ENTRY_32BIT_CS] = GDT_ENTRY(0xc09b, 0, 0xfffff),
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/* DS: data, read/write, 4 GB, base 0 */
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[GDT_ENTRY_32BIT_DS] = GDT_ENTRY(0xc093, 0, 0xfffff),
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/* 16-bit CS: code, read/execute, 64 kB, base 0 */
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[GDT_ENTRY_16BIT_CS] = GDT_ENTRY(0x109b, 0, 0x0ffff),
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/* 16-bit DS: data, read/write, 64 kB, base 0 */
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[GDT_ENTRY_16BIT_DS] = GDT_ENTRY(0x1093, 0, 0x0ffff),
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};
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static struct gdt_ptr gdt;
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gdt.len = sizeof(boot_gdt)-1;
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gdt.ptr = (u32)&boot_gdt;
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asm volatile("lgdtl %0\n" \
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"movl $((2+1)*8), %%ecx\n" \
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"movl %%ecx, %%ds\n" \
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"movl %%ecx, %%es\n" \
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"movl %%ecx, %%fs\n" \
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"movl %%ecx, %%gs\n" \
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"movl %%ecx, %%ss" \
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: : "m" (gdt) : "ecx");
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}
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int cpu_init_f(void)
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{
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/* initialize FPU, reset EM, set MP and NE */
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@ -51,6 +106,8 @@ int cpu_init_f(void)
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int cpu_init_r(void)
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{
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reload_gdt();
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/* Initialize core interrupt and exception functionality of CPU */
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cpu_init_interrupts ();
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return 0;
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@ -100,53 +100,6 @@ mem_init_ret:
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jmp get_mem_size
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get_mem_size_ret:
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/*
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* We are now in 'Flat Protected Mode' and we know how much memory
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* the board has. The (temporary) Global Descriptor Table is not
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* in a 'Safe' place (it is either in Flash which can be erased or
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* reprogrammed or in a fail-safe boot-strap image which could be
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* over-written).
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*
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* Move the final gdt to a safe place (top of RAM) and load it.
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* This is not a trivial excercise - the lgdt instruction does not
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* have a register operand (memory only) and we may well be
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* running from Flash, so self modifying code will not work here.
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* To overcome this, we copy a stub into upper memory along with
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* the GDT.
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*/
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/* Reduce upper memory limit by (Stub + GDT Pointer + GDT) */
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subl $(end_gdt_setup - start_gdt_setup), %eax
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/* Copy the GDT and Stub */
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movl $start_gdt_setup, %esi
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movl %eax, %edi
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movl $(end_gdt_setup - start_gdt_setup), %ecx
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shrl $2, %ecx
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cld
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rep movsl
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/* write the lgdt 'parameter' */
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subl $(jmp_instr - start_gdt_setup - 4), %ebp
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addl %eax, %ebp
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movl $(gdt_ptr - start_gdt_setup), %ebx
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addl %eax, %ebx
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movl %ebx, (%ebp)
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/* write the gdt address into the pointer */
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movl $(gdt_addr - start_gdt_setup), %ebp
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addl %eax, %ebp
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movl $(gdt - start_gdt_setup), %ebx
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addl %eax, %ebx
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movl %ebx, (%ebp)
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/* Save the return address */
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movl $load_gdt_ret, %ebp
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/* Load the new (safe) Global Descriptor Table */
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jmp *%eax
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load_gdt_ret:
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/* Check we have enough memory for stack */
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movl $CONFIG_SYS_STACK_SIZE, %ecx
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cmpl %ecx, %eax
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@ -221,52 +174,3 @@ die: hlt
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blank_idt_ptr:
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.word 0 /* limit */
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.long 0 /* base */
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.align 4
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start_gdt_setup:
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lgdt gdt_ptr
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jmp_instr:
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jmp *%ebp
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.align 4
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gdt_ptr:
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.word 0x30 /* limit (48 bytes = 6 GDT entries) */
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gdt_addr:
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.long gdt /* base */
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/* The GDT table ...
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*
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* Selector Type
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* 0x00 NULL
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* 0x08 Unused
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* 0x10 32bit code
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* 0x18 32bit data/stack
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* 0x20 16bit code
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* 0x28 16bit data/stack
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*/
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.align 4
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gdt:
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.word 0, 0, 0, 0 /* NULL */
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.word 0, 0, 0, 0 /* unused */
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.word 0xFFFF /* 4Gb - (0x100000*0x1000 = 4Gb) */
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.word 0 /* base address = 0 */
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.word 0x9B00 /* code read/exec */
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.word 0x00CF /* granularity = 4096, 386 (+5th nibble of limit) */
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.word 0xFFFF /* 4Gb - (0x100000*0x1000 = 4Gb) */
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.word 0x0 /* base address = 0 */
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.word 0x9300 /* data read/write */
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.word 0x00CF /* granularity = 4096, 386 (+5th nibble of limit) */
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.word 0xFFFF /* 64kb */
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.word 0 /* base address = 0 */
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.word 0x9b00 /* data read/write */
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.word 0x0010 /* granularity = 1 (+5th nibble of limit) */
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.word 0xFFFF /* 64kb */
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.word 0 /* base address = 0 */
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.word 0x9300 /* data read/write */
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.word 0x0010 /* granularity = 1 (+5th nibble of limit) */
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end_gdt_setup:
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