/**
* @file
*
* @ingroup i386_shared
*
* @brief Real mode interrupt call implementation
*/
/*
* Copyright (c) 2014 - CTU in Prague
* Jan Doležal ( dolezj21@fel.cvut.cz )
*
* The license and distribution terms for this file may be
* found in the file LICENSE in this distribution or at
* http://www.rtems.org/license/LICENSE.
*/
#include <bsp/realmode_int.h>
#include <string.h>
#include <rtems/score/cpu.h>
/*
* offsets to \a i386_realmode_interrupt_registers declared in realmode_int.h
* used in inline assmbler for better readability
*/
#define IR_EAX_OFF "0x00"
#define IR_EBX_OFF "0x04"
#define IR_ECX_OFF "0x08"
#define IR_EDX_OFF "0x0C"
#define IR_ESI_OFF "0x10"
#define IR_EDI_OFF "0x14"
#define IR_DS_OFF "0x18"
#define IR_ES_OFF "0x1A"
#define IR_FS_OFF "0x1C"
#define IR_GS_OFF "0x1E"
/*
* offsets to \a rm_int_regs_bkp_param
*/
#define BKP_ESP_OFF "0x20"
#define BKP_SS_OFF "0x24"
#define BKP_DS_OFF "0x26"
#define RM_ENTRY "0x28"
#define PM_ENTRY "0x2C"
/**
* @brief parameters, results, backup values accessible in real mode
*
* @note Struct members not necessarily used in C. This serves also as
* layout of memory and it is used within inline assembler.
*/
typedef struct {
i386_realmode_interrupt_registers inoutregs;
/** spot for back up of protected mode stack pointer */
uint32_t pm_esp_bkp;
/** spot for back up of protected mode stack selector */
uint16_t pm_ss_bkp;
/** spot for back up of protected mode data selector */
uint16_t ds_bkp;
/** spot for setting up long indirect jump offset
to real mode from 16bit protected mode */
uint16_t rm_entry;
/** spot for setting up long indirect jump segment
to real mode from 16bit protected mode */
uint16_t rm_code_segment;
/** returning offset for long indirect jump back
to 32bit protected mode */
uint32_t pm_entry;
/** returning selector for long indirect jump back
to 32bit protected mode */
uint16_t pm_code_selector;
/* if this struct is to be modified update offset definitions as well */
} RTEMS_PACKED rm_int_regs_bkp_param;
/* offsets to \a pm_bkp_and_param */
#define BKP_IDTR_LIM "0x00"
#define BKP_IDTR_BASE "0x02"
#define BKP_ES_OFF "0x06"
#define BKP_FS_OFF "0x08"
#define BKP_GS_OFF "0x0A"
#define RML_ENTRY "0x0C"
#define RML_D_SEL "0x12"
#define RM_SS "0x14"
#define RM_SP "0x16"
#define RM_DS "0x18"
/**
* @brief backup values, pointers/parameters accessible in protected mode
*
* @note Struct members not necessarily used in C. This serves also as
* layout of memory and it is used within inline assembler.
*/
typedef struct {
/** spot for backup protected mode interrupt descriptor table register */
uint16_t idtr_lim_bkp;
/** @see idtr_lim_bkp */
uint32_t idtr_base_bkp;
/** spot to backup of ES register value in 32bit protected mode */
uint16_t es_bkp;
/** spot to backup of FS register value in 32bit protected mode */
uint16_t fs_bkp;
/** spot to backup of GS register value in 32bit protected mode */
uint16_t gs_bkp;
/** values for indirect jump to 16bit protected mode */
uint32_t rml_entry;
/** @see rml_entry */
uint16_t rml_code_selector;
/** data selector for 16bit protected mode */
uint16_t rml_data_selector;
/** values determinig location of real mode stack */
uint16_t rm_stack_segment;
/** @see rm_stack_segment */
uint16_t rm_stack_pointer;
/** data segment for real mode */
uint16_t rm_data_segment;
} RTEMS_PACKED pm_bkp_and_param;
/* addresses where we are going to put Interrupt buffer,
* parameter/returned/preserved values, stack and copy code
* for calling BIOS interrupt real mode interface
* The value is chosen arbitrarily in the first 640kB
* to be accessible for real mode. It should be out of range
* used by RTEMS because its base address is above 1MB.
* It has to be above first 4kB (or better 64kB) which could
* be used by BIOS.
*/
#define REAL_MODE_SPOT 0x12000
/* REAL_MODE_SPOT value is also top of real mode stack */
/* buffers positions and lengths */
#define DEFAULT_BUFFER_SIZE 512
static void *default_rm_buffer_spot = (void *)REAL_MODE_SPOT;
static uint16_t default_rm_buffer_size = DEFAULT_BUFFER_SIZE;
/* real mode stack */
#define STACK_SIZE 8192
#define INT_STACK_TOP REAL_MODE_SPOT
/******************************
* STACK * *
****************************** REAL_MODE_SPOT
* INT_BUF * 512 B *
******************************
* INT_REGs * 50 B *
******************************
* INT_FNC *~149 B *
******************************/
#define __DP_TYPE uint8_t
#define __DP_YES ((__DP_TYPE)1)
#define __DP_NO ((__DP_TYPE)-1)
#define __DP_FAIL ((__DP_TYPE)0)
static __DP_TYPE descsPrepared = __DP_NO;
/* rml - real mode alike */
#define rml_limit 0xFFFF
static uint16_t rml_code_dsc_index = 0;
static uint16_t rml_data_dsc_index = 0;
/**
* @brief Prepares real-mode like descriptors to be used for switching
* to real mode.
*
* Descriptors will be placed to the GDT.
*
* @param[in] base32 32-bit physical address to be used as base for 16-bit
* protected mode descriptors
* @retval __DP_YES descriptors are prepared
* @retval __DP_FAIL descriptors allocation failed (GDT too small)
*/
static __DP_TYPE prepareRMDescriptors (void *base32) {
static void *prevBase = (void *)-1;
/* check if descriptors were prepared already */
if (descsPrepared == __DP_YES && prevBase == base32)
return descsPrepared;
if (descsPrepared == __DP_FAIL)
return descsPrepared;
/* create 'real mode like' segment descriptors, for switching to real mode */
rml_code_dsc_index = i386_next_empty_gdt_entry();
if (rml_code_dsc_index == 0)
{
/* not enough space in GDT */
descsPrepared = __DP_FAIL;
return descsPrepared;
}
segment_descriptors flags_desc;
memset(&flags_desc, 0, sizeof(flags_desc));
flags_desc.type = 0xE; /* bits 4 */
flags_desc.descriptor_type = 0x1; /* bits 1 */
flags_desc.privilege = 0x0; /* bits 2 */
flags_desc.present = 0x1; /* bits 1 */
flags_desc.available = 0x0; /* bits 1 */
flags_desc.fixed_value_bits = 0x0; /* bits 1 */
flags_desc.operation_size = 0x0; /* bits 1 */
flags_desc.granularity = 0x0; /* bits 1 */
i386_fill_segment_desc_base((unsigned)base32, &flags_desc);
i386_fill_segment_desc_limit(rml_limit, &flags_desc);
if (i386_raw_gdt_entry(rml_code_dsc_index, &flags_desc) == 0)
{
/* selector to GDT out of range */
descsPrepared = __DP_FAIL;
return descsPrepared;
}
rml_data_dsc_index = i386_next_empty_gdt_entry();
if (rml_data_dsc_index == 0)
{
/* not enough space in GDT for both descriptors */
descsPrepared = __DP_FAIL;
return descsPrepared;
}
flags_desc.type = 0x2; /* bits 4 */
if (i386_raw_gdt_entry(rml_data_dsc_index, &flags_desc) == 0)
{
/* selector to GDT out of range */
descsPrepared = __DP_FAIL;
return descsPrepared;
}
prevBase = base32;
descsPrepared = __DP_YES;
return descsPrepared;
}
void *i386_get_default_rm_buffer(uint16_t *size) {
*size = default_rm_buffer_size;
return default_rm_buffer_spot;
}
int i386_real_interrupt_call(uint8_t interrupt_number,
i386_realmode_interrupt_registers *ir)
{
uint32_t pagingon;
rm_int_regs_bkp_param *int_passed_regs_spot;
/* place where the code switching to realmode and executing
interrupt is coppied */
void *rm_swtch_code_dst;
void *rm_stack_top;
size_t cpLength;
void *cpBeg;
/* values that can be passed from protected mode are stored in this struct
and they are passed later to the inline assembler executing interrupt */
volatile pm_bkp_and_param pm_bkp, *pm_bkp_addr;
unsigned short unused_offset;
__asm__ volatile( "\t"
"movl %%cr0, %%eax\n\t"
"andl %1, %%eax\n"
: "=a"(pagingon)
: "i"(CR0_PAGING)
);
if (pagingon)
return 0;
/* located under 1MB for real mode to be able to get/set values */
int_passed_regs_spot = (rm_int_regs_bkp_param *)
(default_rm_buffer_spot+default_rm_buffer_size);
/* position for real mode code reallocation to the first 1MB of RAM */
rm_swtch_code_dst = (void *)((uint32_t)int_passed_regs_spot +
sizeof(*int_passed_regs_spot));
rm_stack_top = (void *)INT_STACK_TOP;
if (prepareRMDescriptors(int_passed_regs_spot) != __DP_YES)
return 0;
pm_bkp_addr = &pm_bkp;
i386_Physical_to_real(
rm_stack_top - STACK_SIZE,
(unsigned short *)&pm_bkp.rm_stack_segment,
(unsigned short *)&pm_bkp.rm_stack_pointer
);
pm_bkp.rm_stack_pointer += STACK_SIZE;
pm_bkp.rml_code_selector = (rml_code_dsc_index<<3);
pm_bkp.rml_entry = ((uint32_t)rm_swtch_code_dst -
(uint32_t)int_passed_regs_spot);
pm_bkp.rml_data_selector = (rml_data_dsc_index<<3);
i386_Physical_to_real(
int_passed_regs_spot,
(unsigned short *)&pm_bkp.rm_data_segment,
&unused_offset
);
int_passed_regs_spot->inoutregs = *ir;
/* offset from the beginning of coppied code */
uint16_t rm_entry_offset;
__asm__ volatile(
"movw $(rment-cp_beg), %0\n\t"
: "=r"(rm_entry_offset)
);
i386_Physical_to_real(
rm_swtch_code_dst+rm_entry_offset,
(unsigned short *)&int_passed_regs_spot->rm_code_segment,
(unsigned short *)&int_passed_regs_spot->rm_entry
);
__asm__ volatile(
"movl $(cp_end), %0\n\t"
"movw %%cs, %1\n\t"
: "=mr"(int_passed_regs_spot->pm_entry),
"=mr"(int_passed_regs_spot->pm_code_selector)
);
/* copy code for switch to real mode and
executing interrupt to first MB of RAM */
__asm__ volatile( "\t"
"mov $cp_end-cp_beg, %0\n\t"
"mov $cp_beg, %1\n\t"
: "=rm"(cpLength), "=rm"(cpBeg)
);
memcpy(rm_swtch_code_dst, cpBeg, cpLength);
/* write interrupt number to be executed */
uint16_t interrupt_number_off;
uint8_t *interrupt_number_ptr;
__asm__ volatile( "\t"
"movw $intnum-cp_beg, %0\n\t"
: "=rm"(interrupt_number_off)
);
interrupt_number_ptr = (uint8_t *)(rm_swtch_code_dst+interrupt_number_off);
*interrupt_number_ptr = interrupt_number;
/* execute code that jumps to coppied function, which switches to real mode,
loads registers with values passed to interrupt and executes interrupt */
__asm__ volatile( "\t"
/* backup stack */
"movl %[regs_spot], %%ebx\n\t"
"movl %%esp, "BKP_ESP_OFF"(%%ebx)\n\t"
"movw %%ss, "BKP_SS_OFF"(%%ebx)\n\t"
/* backup data selector */
"movw %%ds, "BKP_DS_OFF"(%%ebx)\n\t"
/* backup other selectors */
"movl %[pm_bkp], %%esi\n\t"
"movw %%es, "BKP_ES_OFF"(%%esi)\n\t"
"movw %%fs, "BKP_FS_OFF"(%%esi)\n\t"
"movw %%gs, "BKP_GS_OFF"(%%esi)\n\t"
/* hopefully loader does not damage interrupt table on the beginning of
memory; that means length: 0x3FF, base: 0x0 */
/* preserve idtr */
"movl %%esi, %%eax\n\t"
"addl $"BKP_IDTR_LIM", %%eax\n\t"
"cli\n\t"
"sidt (%%eax)\n\t"
"movl $rmidt, %%eax\n\t"
"lidt (%%eax)\n\t"
/* prepare 'real mode like' data selector */
"movw "RML_D_SEL"(%%esi), %%ax\n\t"
/* prepare real mode data segment value */
"xorl %%edx,%%edx\n\t"
"movw "RM_DS"(%%esi), %%dx\n\t"
/* prepare real mode stack values */
"movw "RM_SS"(%%esi), %%cx\n\t"
"movzwl "RM_SP"(%%esi), %%esp\n\t"
/* jump to copied function and */
/* load 'real mode like' code selector */
"ljmp *"RML_ENTRY"(%%esi)\n"
"rmidt:"/* limit and base for realmode interrupt descriptor table */
".word 0x3FF\n\t"
".long 0\n\t"
/* load 'real mode like' data selectors */
"cp_beg: .code16\n\t"
"movw %%ax, %%ss\n\t"
"movw %%ax, %%ds\n\t"
"movw %%ax, %%es\n\t"
"movw %%ax, %%fs\n\t"
"movw %%ax, %%gs\n\t"
/* disable protected mode */
"movl %%cr0, %%eax\n\t"
"and %[cr0_prot_dis], %%ax\n\t"
"movl %%eax, %%cr0\n\t"
/* base for data selector of 16-bit protected mode is
at beginning of passed regs */
/* flush prefetch queue by far jumping */
"ljmp *"RM_ENTRY"\n\t"
"rment: "
/* establish rm stack - esp was already set in 32-bit protected mode*/
"movw %%cx, %%ss\n\t"
/* set data segment (value prepared in 32-bit prot mode) */
"movw %%dx, %%ds\n\t"
/* count real mode pointer so we don't need to overuse address
prefix (by using 32bit addresses in 16bit context) */
"shll $4,%%edx\n\t"
"subl %%edx,%%ebx\n\t"
/* prepare values to be used after interrupt call */
"pushw %%bx\n\t"
"pushw %%ds\n\t"
/* fill registers with parameters */
"movw " IR_DS_OFF"(%%bx), %%ax\n\t"
"pushw %%ax\n\t"
"movl "IR_EAX_OFF"(%%bx), %%eax\n\t"
"movl "IR_ECX_OFF"(%%bx), %%ecx\n\t"
"movl "IR_EDX_OFF"(%%bx), %%edx\n\t"
"movl "IR_EDI_OFF"(%%bx), %%edi\n\t"
"movl "IR_ESI_OFF"(%%bx), %%esi\n\t"
"movw " IR_ES_OFF"(%%bx), %%es\n\t"
"movw " IR_FS_OFF"(%%bx), %%fs\n\t"
"movw " IR_GS_OFF"(%%bx), %%gs\n\t"
/* prepare ebx register */
"movl "IR_EBX_OFF"(%%bx), %%ebx\n\t"
/* prepare ds */
"popw %%ds\n\t"
/* interrupt instruction */
".byte 0xCD\n\t"
"intnum: .byte 0x0\n\t"
/* fill return structure */
"pushw %%ds\n\t"
"pushl %%ebx\n\t"
"movw 0x6(%%esp), %%ds\n\t"
"movw 0x8(%%esp),%%bx\n\t" /* regs_spot */
"movl %%eax,"IR_EAX_OFF"(%%bx)\n\t"
"popl %%eax\n\t"
"movl %%eax,"IR_EBX_OFF"(%%bx)\n\t"
"movl %%ecx,"IR_ECX_OFF"(%%bx)\n\t"
"movl %%edx,"IR_EDX_OFF"(%%bx)\n\t"
"movl %%esi,"IR_ESI_OFF"(%%bx)\n\t"
"movl %%edi,"IR_EDI_OFF"(%%bx)\n\t"
"popw %%ax\n\t"
"movw %%ax, " IR_DS_OFF"(%%bx)\n\t"
"movw %%es, " IR_ES_OFF"(%%bx)\n\t"
"movw %%fs, " IR_FS_OFF"(%%bx)\n\t"
"movw %%gs, " IR_GS_OFF"(%%bx)\n\t"
/* prepare protected mode data segment */
"movw "BKP_DS_OFF"(%%bx), %%ax\n\t"
/* restore protected mode stack values */
"movl "BKP_ESP_OFF"(%%bx),%%esp\n\t"
"movw "BKP_SS_OFF"(%%bx), %%dx\n\t"
/* return to protected mode */
"movl %%cr0, %%ecx \n\t"
"or %[cr0_prot_ena], %%cx\n\t"
"movl %%ecx, %%cr0 \n\t"
"ljmpl *"PM_ENTRY"(%%bx)\n\t"
".code32\n"
/* reload segmentation registers */
"cp_end:"
"movw %%ax, %%ds\n\t"
/* restore stack segment in protected mode context */
"movw %%dx, %%ss\n\t"
"movl %[pm_bkp], %%esi\n\t"
"movw "BKP_ES_OFF"(%%esi), %%es\n\t"
"movw "BKP_FS_OFF"(%%esi), %%fs\n\t"
"movw "BKP_GS_OFF"(%%esi), %%gs\n\t"
/* restore IDTR */
"addl $"BKP_IDTR_LIM", %%esi\n\t"
"lidt (%%esi)\n\t"
:
: [regs_spot]"m"(int_passed_regs_spot),
[pm_bkp]"m"(pm_bkp_addr),
[cr0_prot_ena]"i"(CR0_PROTECTION_ENABLE),
[cr0_prot_dis]"i"(~CR0_PROTECTION_ENABLE)
: "memory", "ebx", "ecx", "edx", "esi", "edi"
);
*ir = int_passed_regs_spot->inoutregs;
return 1;
}
