Code for actual protected-mode entry

This is the code which actually does the switch to protected mode,
including all preparation.  It is also responsible for invoking the
boot loader hooks, if present.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/i386/boot/pm.c b/arch/i386/boot/pm.c
new file mode 100644 (file)
index 0000000..3fa53e1
--- /dev/null
+++ b/arch/i386/boot/pm.c
@@ -0,0 +1,170 @@
+/* -*- linux-c -*- ------------------------------------------------------- *
+ *
+ *   Copyright (C) 1991, 1992 Linus Torvalds
+ *   Copyright 2007 rPath, Inc. - All Rights Reserved
+ *
+ *   This file is part of the Linux kernel, and is made available under
+ *   the terms of the GNU General Public License version 2.
+ *
+ * ----------------------------------------------------------------------- */
+
+/*
+ * arch/i386/boot/pm.c
+ *
+ * Prepare the machine for transition to protected mode.
+ */
+
+#include "boot.h"
+#include <asm/segment.h>
+
+/*
+ * Invoke the realmode switch hook if present; otherwise
+ * disable all interrupts.
+ */
+static void realmode_switch_hook(void)
+{
+       if (boot_params.hdr.realmode_swtch) {
+               asm volatile("lcallw *%0"
+                            : : "m" (boot_params.hdr.realmode_swtch)
+                            : "eax", "ebx", "ecx", "edx");
+       } else {
+               asm volatile("cli");
+               outb(0x80, 0x70); /* Disable NMI */
+               io_delay();
+       }
+}
+
+/*
+ * A zImage kernel is loaded at 0x10000 but wants to run at 0x1000.
+ * A bzImage kernel is loaded and runs at 0x100000.
+ */
+static void move_kernel_around(void)
+{
+       /* Note: rely on the compile-time option here rather than
+          the LOADED_HIGH flag.  The Qemu kernel loader unconditionally
+          sets the loadflags to zero. */
+#ifndef __BIG_KERNEL__
+       u16 dst_seg, src_seg;
+       u32 syssize;
+
+       dst_seg =  0x1000 >> 4;
+       src_seg = 0x10000 >> 4;
+       syssize = boot_params.hdr.syssize; /* Size in 16-byte paragraphs */
+
+       while (syssize) {
+               int paras  = (syssize >= 0x1000) ? 0x1000 : syssize;
+               int dwords = paras << 2;
+
+               asm volatile("pushw %%es ; "
+                            "pushw %%ds ; "
+                            "movw %1,%%es ; "
+                            "movw %2,%%ds ; "
+                            "xorw %%di,%%di ; "
+                            "xorw %%si,%%si ; "
+                            "rep;movsl ; "
+                            "popw %%ds ; "
+                            "popw %%es"
+                            : "+c" (dwords)
+                            : "rm" (dst_seg), "rm" (src_seg)
+                            : "esi", "edi");
+
+               syssize -= paras;
+               dst_seg += paras;
+               src_seg += paras;
+       }
+#endif
+}
+
+/*
+ * Disable all interrupts at the legacy PIC.
+ */
+static void mask_all_interrupts(void)
+{
+       outb(0xff, 0xa1);       /* Mask all interrupts on the seconday PIC */
+       io_delay();
+       outb(0xfb, 0x21);       /* Mask all but cascade on the primary PIC */
+       io_delay();
+}
+
+/*
+ * Reset IGNNE# if asserted in the FPU.
+ */
+static void reset_coprocessor(void)
+{
+       outb(0, 0xf0);
+       io_delay();
+       outb(0, 0xf1);
+       io_delay();
+}
+
+/*
+ * Set up the GDT
+ */
+#define GDT_ENTRY(flags,base,limit)            \
+       (((u64)(base & 0xff000000) << 32) |     \
+        ((u64)flags << 40) |                   \
+        ((u64)(limit & 0x00ff0000) << 32) |    \
+        ((u64)(base & 0x00ffff00) << 16) |     \
+        ((u64)(limit & 0x0000ffff)))
+
+struct gdt_ptr {
+       u16 len;
+       u32 ptr;
+} __attribute__((packed));
+
+static void setup_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_BOOT_CS] = GDT_ENTRY(0xc09b, 0, 0xfffff),
+               /* DS: data, read/write, 4 GB, base 0 */
+               [GDT_ENTRY_BOOT_DS] = GDT_ENTRY(0xc093, 0, 0xfffff),
+       };
+       struct gdt_ptr gdt;
+
+       gdt.len = sizeof(boot_gdt)-1;
+       gdt.ptr = (u32)&boot_gdt + (ds() << 4);
+
+       asm volatile("lgdtl %0" : : "m" (gdt));
+}
+
+/*
+ * Set up the IDT
+ */
+static void setup_idt(void)
+{
+       static const struct gdt_ptr null_idt = {0, 0};
+       asm volatile("lidtl %0" : : "m" (null_idt));
+}
+
+/*
+ * Actual invocation sequence
+ */
+void go_to_protected_mode(void)
+{
+       /* Hook before leaving real mode, also disables interrupts */
+       realmode_switch_hook();
+
+       /* Move the kernel/setup to their final resting places */
+       move_kernel_around();
+
+       /* Enable the A20 gate */
+       if (enable_a20()) {
+               puts("A20 gate not responding, unable to boot...\n");
+               die();
+       }
+
+       /* Reset coprocessor (IGNNE#) */
+       reset_coprocessor();
+
+       /* Mask all interrupts in the PIC */
+       mask_all_interrupts();
+
+       /* Actual transition to protected mode... */
+       setup_idt();
+       setup_gdt();
+       protected_mode_jump(boot_params.hdr.code32_start,
+                           (u32)&boot_params + (ds() << 4));
+}

diff --git a/arch/i386/boot/pmjump.S b/arch/i386/boot/pmjump.S
new file mode 100644 (file)
index 0000000..2e55923
--- /dev/null
+++ b/arch/i386/boot/pmjump.S
@@ -0,0 +1,54 @@
+/* ----------------------------------------------------------------------- *
+ *
+ *   Copyright (C) 1991, 1992 Linus Torvalds
+ *   Copyright 2007 rPath, Inc. - All Rights Reserved
+ *
+ *   This file is part of the Linux kernel, and is made available under
+ *   the terms of the GNU General Public License version 2.
+ *
+ * ----------------------------------------------------------------------- */
+
+/*
+ * arch/i386/boot/pmjump.S
+ *
+ * The actual transition into protected mode
+ */
+
+#include <asm/boot.h>
+#include <asm/segment.h>
+
+       .text
+
+       .globl  protected_mode_jump
+       .type   protected_mode_jump, @function
+
+       .code16
+
+/*
+ * void protected_mode_jump(u32 entrypoint, u32 bootparams);
+ */
+protected_mode_jump:
+       xorl    %ebx, %ebx              # Flag to indicate this is a boot
+       movl    %edx, %esi              # Pointer to boot_params table
+       movl    %eax, 2f                # Patch ljmpl instruction
+       jmp     1f                      # Short jump to flush instruction q.
+
+1:
+       movw    $__BOOT_DS, %cx
+
+       movl    %cr0, %edx
+       orb     $1, %dl                 # Protected mode (PE) bit
+       movl    %edx, %cr0
+
+       movw    %cx, %ds
+       movw    %cx, %es
+       movw    %cx, %fs
+       movw    %cx, %gs
+       movw    %cx, %ss
+
+       # Jump to the 32-bit entrypoint
+       .byte   0x66, 0xea              # ljmpl opcode
+2:     .long   0                       # offset
+       .word   __BOOT_CS               # segment
+
+       .size   protected_mode_jump, .-protected_mode_jump