segment.c

Go to the documentation of this file.

#include <slibc.h>
#include <sys/types.h>
#include <stdio.h>
#include <stddef.h>
#include <string.h>

#include <segment.h>

#define GDT_SET(entry, t, d, b, l) \
do { \
        unsigned long limit; \
        (entry).type = (t); \
        (entry).dpl = (d); \
        (entry).s = 1; \
        (entry).p = 1; \
        (entry).avl = 0; \
        (entry).zero = 0; \
        (entry).size = 1; \
        (entry).g = 1; \
        (entry).base0 = (b) & 0x0000FFFFu; \
        (entry).base1 = ((b) & 0x00FF0000u) >> 16; \
        (entry).base2 = ((b) >> 24) & 0x0FFu; \
        limit = (entry).g ? ((l) >> 12) : ((l) & 0x000FFFFF); \
        (entry).limit0 = limit & 0x0000FFFFu; \
        (entry).limit1 = (limit >> 16) & 0x0000000Fu; \
} while (0)

#define TSS_SET(entry, d, b, l) \
do { \
        unsigned long limit; \
        (entry).type = 0x09; \
        (entry).dpl = (d); \
        (entry).p = 1; \
        (entry).avl = 0; \
        (entry).zero1 = 0; \
        (entry).zero2 = 0; \
        (entry).g = 0; \
        (entry).base_low = (b) & 0x0000FFFF; \
        (entry).base_high_low = ((b) & 0x00FF0000) >> 16; \
        (entry).base_high_high= ((b) >> 24) & 0x000000FF; \
        limit = (entry).g ? ((l) >> 12) : ((l) & 0x000FFFFF); \
        (entry).segment_limit_low = limit & 0x0000FFFFu; \
        (entry).segment_limit_high = (limit >> 16) & 0x0000000Fu; \
} while (0)

static struct segment s_gdt[DESC_COUNT];
static struct tss32 s_tss = {
        .io_map_base_address = (sizeof(s_tss) - IO_BITMAP_SIZE),
        .io_bitmap = { '\0', },
};

void segment_init(void)
{
        struct gdtr gdtr;
        struct tss *tss;

        memset(s_gdt + 0, 0, sizeof(*s_gdt));
        GDT_SET(s_gdt[DESC_KERNEL_CS],
                                CODE | READABLE, KERNEL, 0x0, 0xFFFFFFFF);
        GDT_SET(s_gdt[DESC_KERNEL_DS], WRITABLE, KERNEL, 0x0, 0xFFFFFFFF);
        GDT_SET(s_gdt[DESC_KERNEL_SS], WRITABLE, KERNEL, 0x0, 0xFFFFFFFF);

        GDT_SET(s_gdt[DESC_USER_CS], CODE | READABLE, USER, 0x0, 0xFFFFFFFF);
        GDT_SET(s_gdt[DESC_USER_DS], WRITABLE, USER, 0x0, 0xFFFFFFFF);
        GDT_SET(s_gdt[DESC_USER_SS], WRITABLE, USER, 0x0, 0xFFFFFFFF);

        tss = (struct tss*)(s_gdt + DESC_TSS);
        TSS_SET(*tss, KERNEL, (unsigned long)&s_tss, sizeof(s_tss));

        gdtr.base = (unsigned long)s_gdt;
        gdtr.limit = sizeof(s_gdt) - 1;

        asm volatile ("lgdt (%0)"::"g"(&gdtr));
        asm volatile (
                "ltr %0"
                :
                :"a"((unsigned short)(DESC_TSS << SIZEOF_A_DESC_BIT))
        );
}

unsigned char *tss_io_bitmap_get(void)
{
        return (unsigned char *)s_tss.io_bitmap;
}

void tss_update_kernel_stack(unsigned long esp)
{
        s_tss.ss0 = (DESC_KERNEL_SS << 3) | TI(GDT) | KERNEL;
        s_tss.esp0 = esp;
}

/* End of a file */