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mem.c

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/*!     \file arch/i386/kernel/mem.c
 *      \brief Low level (i386) memory manager.
 *      \author Andrea Righi <drizzt@inwind.it>
 *      \date Last update: 2004-01-20
 *      \note Copyright (&copy;) 2003 Andrea Righi
 *
 *      \n
 *      For a complete documentation about GDT and descriptors
 *      you can see the "IA-32 Intel® Architecture Software Developer's
 *      Manual - Volume 3: System Programming Guide"
 *      (http://www.intel.com/design/pentium4/manuals).
 *      \n
 *      For an intalian documentation you can download the
 *      "Minirighi32 - Documentazione Ufficiale"
 *      (http://sourceforge.net/project/showfiles.php?group_id=80923&release_id=180542).
 *
 */

#include <const.h>

#include <arch/i386.h>
#include <arch/paging.h>

#include <kernel/console.h>
#include <kernel/kernel.h>
#include <kernel/task.h>

#include <arch/mem.h>

//! Global Descriptor Table (GDT).
volatile gdt_entry_t gdt[GDT_DIM];
//! GDT pointer.
static gdt_reg gdt_ptr;

//! \brief Initialize a GDT entry.
//! \param limit The size of the memory segment.
//! \param base The starting linear address of the memory segment.
//! \param attribs0_7
//!             The first 8-bit of the segment descriptor attributes.
//! \param attribs8_15
//!             The last 8-bit of the segment descriptor attributes.
//! \return
//!     The selector of the new GDT entry.
word setup_GDT_entry(word limit, dword base, byte attribs0_7, byte attribs8_15)
{
        // Skip the dummy entry (#0).
        register unsigned short i=1;
        dword IF = GET_IF();

        disable();
        for (; i<GDT_DIM; i++)
        {
                if (!(gdt[i].limit))
                {
                        gdt[i].limit = limit;
                        gdt[i].base0_15 = base & 0xFFFF;
                        gdt[i].base16_23 = (base >> 16) & 0xFF;
                        gdt[i].base24_31 = (base >> 24) & 0xFF;
                        gdt[i].attribs0_7 = attribs0_7;
                        gdt[i].attribs8_15 = attribs8_15;

                        SET_IF(IF);

                        // Return the selector.
                        return(i * GDT_ENTRY_DIM);
                }
        }
        error("Out of GDT entries!");
        return( NULL );
}

//! \brief Remove a GDT entry.
//! \param sel The selector to remove from the GDT.
void remove_GDT_entry(word sel)
{
        dword IF = GET_IF();

        disable();

        gdt[sel/GDT_ENTRY_DIM].limit = 0;
        gdt[sel/GDT_ENTRY_DIM].base0_15 = 0;
        gdt[sel/GDT_ENTRY_DIM].base16_23 = 0;
        gdt[sel/GDT_ENTRY_DIM].base24_31 = 0;
        gdt[sel/GDT_ENTRY_DIM].attribs0_7 = 0;
        gdt[sel/GDT_ENTRY_DIM].attribs8_15 = 0;

        SET_IF(IF);
}

//! \brief
//!     Initialize the Global Descriptor Table with the default
//!     selectors and update the segment registers.
void install_GDT()
{
        // First of all reset all entries in the GDT //
        memset(&gdt, 0, sizeof(gdt));

        // ------------- Reserved entries in the GDT ------------------ //

        // Dummy descriptor//
        setup_GDT_entry(0, 0, 0, 0);
        // KERNEL_DATA descriptor 0x08 //
        setup_GDT_entry(0xFFFF, 0, DATA_SEG, (ATTR_GRANUL | ATTR_32BIT | 0xF));
        // KERNEL_CODE descriptor 0x10 //
        setup_GDT_entry(0xFFFF, 0, CODE_SEG, (ATTR_GRANUL | ATTR_32BIT | 0xF));
        // USER_DATA descriptor 0x18 //
        setup_GDT_entry(0xFFFF, 0, (DATA_SEG | DPL_3), (ATTR_GRANUL | ATTR_32BIT | 0xF));
        // USER_CODE descriptor 0x20 //
        setup_GDT_entry(0xFFFF, 0, (CODE_SEG | DPL_3), (ATTR_GRANUL | ATTR_32BIT | 0xF));

        // --------- End of reserved entries in the GDT --------------- //

        // Set up the GDT pointer //
        gdt_ptr.limit = (uint16_t)(GDT_DIM * GDT_ENTRY_DIM - 1);
        gdt_ptr.base = (size_t)gdt;

        // Load info into GDTR //
        __asm__ __volatile__ ("lgdtl (%0)" : : "r"(&gdt_ptr));

        // Update segment registers //
        k_update_segment_regs();
}

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