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x86: Initialize Global Descriptor Table

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This patch adds code to initialize the Global Descriptor Table. For
simplicity, the memory is organized following the flat model. Thus,
memory appears to Contiki as a single, continuous address space. Code,
data, and stack are all contained in this address space (so called
linear address space).

The macros to manipulate bits from segment descriptor and the
set_descriptor() helper are based on the ones described in [1].

[1] http://wiki.osdev.org/GDT_Tutorial
This commit is contained in:
Andre Guedes 2015-04-01 11:46:29 -03:00 committed by Jesus Sanchez-Palencia
parent 6ecc4a7371
commit 41bca35c1e
3 changed files with 173 additions and 1 deletions
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2
cpu/x86/Makefile.x86
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@ -1,6 +1,6 @@
CONTIKI_CPU_DIRS = .
CONTIKI_SOURCEFILES += mtarch.c
CONTIKI_SOURCEFILES += mtarch.c gdt.c
### Compiler definitions
CC = gcc

136
cpu/x86/gdt.c Normal file
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@ -0,0 +1,136 @@
/*
* Copyright (C) 2015, Intel Corporation. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* 3. Neither the name of the copyright holder nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
* OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include <stdint.h>
#define NUM_DESC 3
/* Each define here is for a specific flag in the descriptor. Refer to Intel
* Combined Manual (Intel 64 and IA-32 Architectures Software Developer's
* Manual), Vol. 3, Section 3.4.5 for a description of each flag.
*/
#define SEG_DESCTYPE(x) ((x) << 0x04) /* Descriptor type (0 for system, 1 for code/data) */
#define SEG_PRES(x) ((x) << 0x07) /* Present */
#define SEG_SAVL(x) ((x) << 0x0C) /* Available for system use */
#define SEG_LONG(x) ((x) << 0x0D) /* Long mode */
#define SEG_SIZE(x) ((x) << 0x0E) /* Size (0 for 16-bit, 1 for 32) */
#define SEG_GRAN(x) ((x) << 0x0F) /* Granularity (0 for 1B - 1MB, 1 for 4KB - 4GB) */
#define SEG_PRIV(x) (((x) & 0x03) << 0x05) /* Set privilege level (0 - 3) */
#define SEG_DATA_RDWR 0x02 /* Read/Write */
#define SEG_CODE_EXRD 0x0A /* Execute/Read */
#define GDT_CODE_PL0 SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \
SEG_PRIV(0) | SEG_CODE_EXRD
#define GDT_DATA_PL0 SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \
SEG_PRIV(0) | SEG_DATA_RDWR
typedef struct gdtr
{
uint16_t limit;
uint32_t base;
} __attribute__((packed)) gdtr_t;
typedef uint64_t segment_desc_t;
/* From Intel Combined Manual, Vol. 3 , Section 3.5.1: The base addresses of
* the GDT should be aligned on an eight-byte boundary to yield the best
* processor performance.
*/
static segment_desc_t gdt[NUM_DESC] __attribute__ ((aligned (8)));
static void
set_descriptor(unsigned int index, uint32_t base, uint32_t limit, uint16_t flag)
{
segment_desc_t descriptor;
if (index >= NUM_DESC)
return;
/* Create the high 32 bit segment */
descriptor = limit & 0x000F0000; /* set limit bits 19:16 */
descriptor |= (flag << 8) & 0x00F0FF00; /* set type, p, dpl, s, g, d/b, l and avl fields */
descriptor |= (base >> 16) & 0x000000FF; /* set base bits 23:16 */
descriptor |= base & 0xFF000000; /* set base bits 31:24 */
/* Shift by 32 to allow for low part of segment */
descriptor <<= 32;
/* Create the low 32 bit segment */
descriptor |= base << 16; /* set base bits 15:0 */
descriptor |= limit & 0x0000FFFF; /* set limit bits 15:0 */
/* Save descriptor into gdt */
gdt[index] = descriptor;
}
/* This function initializes the Global Offset Table. For simplicity, the
* memory is organized following the flat model. Thus, memory appears to
* Contiki as a single continuous address space. Code, data, and stack
* are all contained in this address space (so called linear address space).
*/
void
gdt_init(void)
{
gdtr_t gdtr;
/* Initialize gdtr structure */
gdtr.limit = sizeof(segment_desc_t) * NUM_DESC - 1;
gdtr.base = (uint32_t) &gdt;
/* Initialize descriptors */
set_descriptor(0, 0, 0, 0);
set_descriptor(1, 0, 0x0FFFFF, GDT_CODE_PL0);
set_descriptor(2, 0, 0x0FFFFF, GDT_DATA_PL0);
/* Load GDTR register and update segment registers.
*
* In protected mode, segment registers should be loaded according to
* the offset in GDT. So DS, SS, ES, FS and GS registers should be
* loadded with 0x10 while CS with 0x08. CS register cannot be changed
* directly. For that reason, we do a far jump.
*/
__asm__ ("lgdt %0\n\t"
"jmp $0x08, $1f\n\t"
"1:\n\t"
"mov $0x10, %%ax\n\t"
"mov %%ax, %%ds\n\t"
"mov %%ax, %%ss\n\t"
"mov %%ax, %%es\n\t"
"mov %%ax, %%fs\n\t"
"mov %%ax, %%gs\n\t"
:
: "m" (gdtr)
);
}

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cpu/x86/gdt.h Normal file
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/*
* Copyright (C) 2015, Intel Corporation. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* 3. Neither the name of the copyright holder nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
* OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#ifndef GDT_H
#define GDT_H
void gdt_init(void);
#endif /* GDT_H */