arch/i386: Boot to kernel main() with proper initial segmentation/paging setup

arch/i386/i386_main.c

@@ -1,30 +0,0 @@
-#include <stdint.h>
-
-void main();
- 
-void i386_main(void)
-{
-   extern uint32_t magic;
- 
-   /* Uncomment the following if you want to be able to access the multiboot header */
-   /* extern void *mbd; */
- 
-   if ( magic != 0x2BADB002 )
-   {
-      /* Something went not according to specs. Print an error */
-      /* message and halt, but do *not* rely on the multiboot */
-      /* data structure. */
-   }
- 
-   /* You could either use multiboot.h */
-   /* (http://www.gnu.org/software/grub/manual/multiboot/multiboot.html#multiboot_002eh) */
-   /* or do your offsets yourself. The following is merely an example. */ 
-   //char * boot_loader_name =(char*) ((long*)mbd)[16];
- 
-   /* Print a letter to screen to see everything is working: */
-   unsigned char *videoram = (unsigned char *)0xB8000;
-   videoram[0] = 65; /* character 'A' */
-   videoram[1] = 0x07; /* light grey (7) on black (0). */
-
-   main();
-}

arch/i386/include/arch/segmentation.h

@@ -0,0 +1,26 @@
+/*
+    Copyright (C) 2012, Aaron Lindsay <aaron@aclindsay.com>
+
+    This file is part of Aedrix.
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License along
+    with this program; if not, write to the Free Software Foundation, Inc.,
+    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#define SEGMENT_SELECTOR_KERNEL_PRIVILEGE  0x0
+#define SEGMENT_SELECTOR_KERNEL_CS         (0x10 | SEGMENT_SELECTOR_KERNEL_PRIVILEGE)
+#define SEGMENT_SELECTOR_KERNEL_DS         (0x18 | SEGMENT_SELECTOR_KERNEL_PRIVILEGE)
+#define SEGMENT_SELECTOR_USER_PRIVILEGE    0x3
+#define SEGMENT_SELECTOR_USER_CS           (0x20 | SEGMENT_SELECTOR_USER_PRIVILEGE)
+#define SEGMENT_SELECTOR_USER_DS           (0x28 | SEGMENT_SELECTOR_USER_PRIVILEGE)

arch/i386/kernel.ld

@@ -2,9 +2,12 @@ ENTRY (start)
 
 SECTIONS
 {
-	. = 0x00100000;
+	. = 0xc0100000;
-	.text ALIGN (0x1000) : { *(.text*) *(.rodata*) }
+	kernel_start = .;
-	.init : {
+	.text ALIGN(0x1000) : AT(ADDR(.text) - 0xc0000000) {
+		*(.text*) *(.rodata*)
+	}
+	.init : AT(ADDR(.init) - 0xc0000000) {
 		early_initcalls_start = .;
 		*(.earlyinitcalls*)
 		early_initcalls_end = .;
@@ -12,7 +15,13 @@ SECTIONS
 		*(.driversubsysinitcalls*)
 		*(.deviceinitcalls*)
 		initcalls_end = .;
+		*(.init*)
 	}
-	.data ALIGN (0x1000) : { *(.data*) }
+	.data ALIGN(0x1000) : AT(ADDR(.data) - 0xc0000000) {
-	.bss : { *(.bss*) *(COMMON*) }
+		*(.data*)
+	}
+	.bss : AT(ADDR(.bss) - 0xc0000000) {
+		*(.bss*) *(COMMON*)
+	}
+	kernel_end = .;
 }

arch/i386/kernel.mk

@@ -22,8 +22,7 @@ aedrix-boot.img: aedrix-kernel.elf
 	$(V)mcopy -i "$@" aedrix-kernel.elf ::kernel.bin
 	$(V)mcopy -i "$@" arch/i386/syslinux.cfg ::syslinux.cfg
 
-OBJS_$(d) := $(d)/start.o \
+OBJS_$(d) := $(d)/start.o
-	$(d)/i386_main.o
 
 KOBJS += $(OBJS_$(d))
 

arch/i386/start.S

@@ -18,39 +18,128 @@
     51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-.global start /* making entry point visible to linker */
+#include <arch/segmentation.h>
 
-/* setting up the Multiboot header - see GRUB docs for details */
+#define KERNEL_START_VIRTUAL 0xc0000000
-.set ALIGN,    1<<0                     /* align loaded modules on page boundaries */
+#define KERNEL_START_PAGE (KERNEL_START_VIRTUAL >> 22)
-.set MEMINFO,  1<<1                     /* provide memory map */
+#define virt_to_phys(addr) (addr - KERNEL_START_VIRTUAL)
-.set FLAGS,    ALIGN | MEMINFO          /* this is the Multiboot 'flag' field */
+
-.set MAGIC,    0x1BADB002               /* 'magic number' lets bootloader find the header */
+#define STACK_SIZE 0x4000 /* 16k */
-.set CHECKSUM, -(MAGIC + FLAGS)         /* checksum required */
+
+/* setup multiboot header */
+#define ALIGN     (1<<0)                   /* align loaded modules on page boundaries */
+#define MEMINFO   (1<<1)                   /* provide memory map */
+#define FLAGS     (ALIGN | MEMINFO)        /* this is the Multiboot 'flag' field */
+#define MAGIC     0x1BADB002               /* 'magic number' lets bootloader find the header */
+#define CHECKSUM  (-(MAGIC + FLAGS))       /* checksum required */
 
 .align 4
 .long MAGIC
 .long FLAGS
 .long CHECKSUM
 
-/* reserve initial kernel stack space */
+/*
-.set STACKSIZE, 0x4000                  /* that is, 16k. */
+ * Kernel entry in assembly for i386 architecture. This handles saving off
-.align 32
+ * multiboot information, setting up initial page tables to map the kernel to
-.lcomm stack, STACKSIZE                 /* reserve 16k stack on a doubleword boundary */
+ * where it is linked against, ensures segmentation is setup right (large segments
-.comm  mbd, 4                           /* we will use this in i386_main */
+ * over entire address range), and finally jumps to the kernel's main() function
-.comm  magic, 4                         /* we will use this in i386_main */
+ * in C.
-
+ */
+.global start
 start:
-    movl  $(stack + STACKSIZE), %esp    /* set up the stack */
+	movl  %eax, virt_to_phys(magic)		/* Save off multiboot magic number */
-    movl  %eax, magic                   /* Multiboot magic number */
+	movl  %ebx, virt_to_phys(mbd)		/* Save off multiboot data structure */
-    movl  %ebx, mbd                     /* Multiboot data structure */
 
-    call  i386_main                     /* call kernel proper */
+	movl $virt_to_phys(init_page_dir), %eax	/* load page directory base register */
+	movl %eax, %cr3
+
+	movl %cr4, %eax
+	orl $0x00000010, %eax			/* set PSE bit for 4mb pages */
+	movl %eax, %cr4
+
+	movl %cr0, %eax
+	orl $0x80000000, %eax			/* set PG bit to enable paging */
+	movl %eax, %cr0
+
+	lea paging_enabled, %eax
+	jmp *%eax
+paging_enabled:
+	movl $0, init_page_dir			/* unmap identity mapping and invalidate */
+	invlpg 0
+
+	movl $(stack + STACK_SIZE), %esp	/* set up the stack */
+
+	/* setup two large kernel segments over entire 4gb address range */
+	pushl $initial_gdt			/* setup the pointer to the GDT */
+	pushw $(INITIAL_GDT_SIZE-1)
+	lgdt (%esp)
+	addl $6, %esp
+	ljmp $SEGMENT_SELECTOR_KERNEL_CS, $gdt_reload	/* long jump to set %cs */
+gdt_reload:
+
+	/* reset remaining segment registers */
+	movl $SEGMENT_SELECTOR_KERNEL_DS, %eax
+	movl %eax, %ds
+	movl %eax, %es
+	movl %eax, %fs
+	movl %eax, %gs
+	movl %eax, %ss
+
+	call main				/* call kernel proper */
 
 	cli
 hang:
 	hlt                                 /* halt machine should kernel return */
 	jmp   hang
 
-.globl atags_ptr
+.section .init
+
+/* Note: if the offsets into the GDT change, they must be updated in arch/segmentation.h */
+.set INITIAL_GDT_SIZE, 8*6
+initial_gdt:
+	.long 0x00000000 /* 0x00 intentionally empty */
+	.long 0x00000000
+	.long 0x00000000 /* 0x08 TODO TSS */
+	.long 0x00000000
+	.long 0x0000ffff /* 0x10 kernel code segment (%cs) */
+	.long 0x00cf9a00
+	.long 0x0000ffff /* 0x18 kernel data segment (%ds) */
+	.long 0x00cf9200
+	.long 0x0000ffff /* 0x20 userspace code segment (%cs) */
+	.long 0x00cffa00
+	.long 0x0000ffff /* 0x28 userspace data segment (%ds) */
+	.long 0x00cff200
+
+.align 0x1000
+init_page_dir:
+	/* This page directory entry identity-maps the first 4MB of the 32-bit physical address space.
+	All bits are clear except the following:
+	bit 7: PS The kernel page is 4MB.
+	bit 1: RW The kernel page is read/write.
+	bit 0: P  The kernel page is present.
+	This entry must be here -- otherwise the kernel will crash immediately after paging is
+	enabled because it can't fetch the next instruction! It's ok to unmap this page later. */
+	.long 0x00000083
+	.rept (KERNEL_START_PAGE - 1)
+		.long 0                 /* Pages before kernel space. */
+	.endr
+	/* This page directory entry defines a 4MB page containing the kernel. */
+	.long 0x00000083
+	.rept (1024 - KERNEL_START_PAGE - 1)
+		.long 0  /* Pages after the kernel image. */
+	.endr
+
+/* reserve initial kernel stack space */
+.align 32
+.lcomm stack, STACK_SIZE		/* reserve stack space on a doubleword boundary */
+
+/* place to store multiboot header information */
+.global mbd
+.comm  mbd, 4				/* we will use this in i386_main */
+.global magic
+.comm  magic, 4				/* we will use this in i386_main */
+
+/* TODO FIXME remove this - needs fix to dependencies first */
+.global atags_ptr
 atags_ptr:
-	.word 0
+	.long 0