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

diff --git a/arch/i386/cpu/cpu.c b/arch/i386/cpu/cpu.c
index bd6aced87374d01e9eb7e05897d65a744c0c4142..ae40384f099aabc193052ea65c0111fa23f43d4a 100644 (file)
--- 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 7def8def8b1d3b2398343fe0efbdc8cd935597b5..3cea04b4ce37bd480ada911f610d9a800e9255b4 100644 (file)
--- 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: