Added usermode support. Usermode code added in a seperate section nam…

…ed "um" and copied into a page frame. The pagetables are built for usermode code and stack at 1GB. Interrupt, exception and system call handlers are using register frames now. Fixed GDT entry for based address. Adding support for kernel memory heap.

README.md

@@ -7,9 +7,12 @@ gcc -m32 -std=gnu99 -nostdlib -nostdinc -fno-builtin -fno-stack-protector -nosta
 as --32 handlr32.S -o handlr32.o<br>
 gcc -m32 -std=gnu99 -nostdlib -nostdinc -fno-builtin -fno-stack-protector -nostartfiles -nodefaultlibs -ffreestanding -fno-pic -Wall -Wextra -Werror -c setup32.c -o setup32.o<br>
 gcc -m32 -std=gnu99 -nostdlib -nostdinc -fno-builtin -fno-stack-protector -nostartfiles -nodefaultlibs -ffreestanding -fno-pic -Wall -Wextra -Werror -c start.c -o start.o<br>
+gcc -m32 -std=gnu99 -nostdlib -nostdinc -fno-builtin -fno-stack-protector -nostartfiles -nodefaultlibs -ffreestanding -fno-pic -Wall -Wextra -Werror -c memory.c -o memory.o<br>
+gcc -m32 -std=gnu99 -nostdlib -nostdinc -fno-builtin -fno-stack-protector -nostartfiles -nodefaultlibs -ffreestanding -fno-pic -Wall -Wextra -Werror -c page32.c -o page32.o<br>
+gcc -m32 -std=gnu99 -nostdlib -nostdinc -fno-builtin -fno-stack-protector -nostartfiles -nodefaultlibs -ffreestanding -fno-pic -Wall -Wextra -Werror -c usermode.c -o usermode.o<br>
 
 
-ld -static -T kernel32.ld -m elf_i386 -nostdlib --nmagic boot32.o util.o system.o setup32.o handlr32.o start.o -o xiskernel.elf<br>
+ld -static -T kernel32.ld -m elf_i386 -nostdlib --nmagic boot32.o util.o system.o setup32.o handlr32.o memory.o page32.o usermode.o start.o -o xiskernel.elf<br>
 objcopy -O binary xiskernel.elf xiskernel.bin<br>
 
 Instructions for building boot loader -<br>

handlr32.S

@@ -14,7 +14,7 @@
 
  .globl common_trap_handler
 
- .globl system_call_handler_3
+ .globl sys_call_handler_128
 
  .globl irq_handler_0
  .globl irq_handler_1
@@ -38,9 +38,22 @@
  .macro DEFINE_IRQ_HANDLER irqn
 
  irq_handler_\irqn:
-
+ pushl $\irqn
  pusha
 
+ push %ds
+ push %es
+ push %fs
+ push %gs
+
+ movl %esp, %ebp
+
+ movl $0x28, %eax 
+ movl %eax, %ds
+ movl %eax, %es
+ movl %eax, %fs
+ movl %eax, %gs
+
  movb $0x20,%al
 
  movb $\irqn, %ah
@@ -52,12 +65,19 @@
 
  outb %al,$0x20
 
- push $\irqn 
+ push %ebp
  call common_interrupt_handler
  addl $4, %esp
 
+ pop %gs
+ pop %fs
+ pop %es
+ pop %ds
+
  popa
 
+ addl $4, %esp
+
  iret
 
  .endm
@@ -68,10 +88,35 @@
 
  sys_call_handler_\syscallnr:
  pushl $\syscallnr
+ pusha
+
+ push %ds
+ push %es
+ push %fs
+ push %gs
+
+ movl %esp, %ebp
+
+ movl $0x28, %eax 
+ movl %eax, %ds
+ movl %eax, %es
+ movl %eax, %fs
+ movl %eax, %gs
+
+ push %ebp
  call common_sys_call_handler
  addl $4, %esp
 
+ pop %gs
+ pop %fs
+ pop %es
+ pop %ds
+
  popa
+
+ addl $4, %esp
+
+ iret
 
  .endm
 
@@ -95,14 +140,34 @@
  DEFINE_IRQ_HANDLER 15
 
  // define system call handlers
- DEFINE_SYS_CALL_HANDLER 3
+ DEFINE_SYS_CALL_HANDLER 128
 
 
 common_trap_handler:
- pushl $0
- pushl $0
+ pusha
+
+ push %ds
+ push %es
+ push %fs
+ push %gs
+
+ movl %esp, %ebp
+
+ movl $0x28, %eax 
+ movl %eax, %ds
+ movl %eax, %es
+ movl %eax, %fs
+ movl %eax, %gs
 
+ push %ebp
  call trap_handler
+ addl $4, %esp
+
+ pop %gs
+ pop %fs
+ pop %es
+ pop %ds
+
+ popa
 
- addl $8,%esp
  iret

kernel32.ld

@@ -9,11 +9,15 @@ SECTIONS
  .text : AT(ADDR(.text) - 0x80000000) {*(.text); }
  .data : AT(ADDR(.data) - 0x80000000) {*(.data); }
  .bss : AT(ADDR(.bss) - 0x80000000) {*(.bss); }
+ . = ALIGN(4096);
+ .um : AT(ADDR(.um) - 0x80000000) {*(.um);}
+ um_size = SIZEOF(um);
  .kernel_data ALIGN(4096) : AT(ADDR(.kernel_data) - 0x80000000) {*(.kernel_data); }
  . = ALIGN(4096);
  _kernel_pg_dir = .;
  _kernel_pg_table_0 = _kernel_pg_dir + 0x1000;
  _kernel_stack_0 = _kernel_pg_table_0 + 0x1000;
  _kernel_stack_0_start = _kernel_stack_0 + 0x2000;
- _kernel_private_data = _kernel_stack_0_start;
+ _kernel_private_data = _kernel_stack_0_start + 8;
+ _kernel_heap_start = (_kernel_private_data + 0x1000) & ~(0xfff);
 }

memory.c

@@ -0,0 +1,31 @@
+/*****************************************************************************/
+/* File: memory.c */
+/* */
+/* Description: Source file for memory allocation code. */
+/* */
+/* Author: Shoily O Rahman <[email protected]> */
+/* */
+/* Date: July 9, 2020 */
+/* */
+/*****************************************************************************/
+
+#include "memory.h"
+
+extern int _kernel_heap_start;
+
+char* heap_ptr;
+
+void init_memory() {
+
+ heap_ptr = (char*)_kernel_heap_start;
+}
+
+void *alloc_mem(int size, int alignment) {
+
+ char *mem_start = (char*)heap_ptr;
+
+ mem_start = (char*)(((int)heap_ptr + (alignment-1)) & ~(alignment-1));
+ heap_ptr = mem_start + size;
+
+ return mem_start; 
+}

memory.h

@@ -0,0 +1,18 @@
+/*****************************************************************************/
+/* File: memory.h */
+/* */
+/* Description: Header file for memory allocation code. */
+/* */
+/* Author: Shoily O Rahman <[email protected]> */
+/* */
+/* Date: July 9, 2020 */
+/* */
+/*****************************************************************************/
+
+#ifndef MEMORY_H
+#define MEMORY_H
+
+void init_memory();
+void *alloc_mem(int size, int alignment);
+
+#endif

page32.c

@@ -0,0 +1,47 @@
+/*****************************************************************************/
+/* File: page32.c */
+/* */
+/* Description: Source file for 32 bit page table handling code. */
+/* */
+/* Author: Shoily O Rahman <[email protected]> */
+/* */
+/* Date: July 9, 2020 */
+/* */
+/*****************************************************************************/
+
+#include "page32.h"
+#include "system.h"
+
+void build_pagetable(pgd_t *pgdir, pte_t **pgtable, int phys_addr, int start, int length, int pgd_flags, int pte_flags) {
+
+ int idx = 0;
+ pgd_t *pgd = pgdir + ((start >> 22) & 0x3ff);
+ pte_t *pte = pgtable[idx] + ((start >> 12) & 0x3ff); 
+ pte_t *last_pte = (pte_t*)(((int)pte + PAGE_SIZE) & ~(PAGE_SIZE-1));
+ int end = start + length;
+
+ if (!*pgd) {
+ *pgd = ((int)pgtable[idx] - KERNEL_VIRT_ADDR) | pgd_flags;
+ }
+
+ while(start < end) {
+
+ if (pte == last_pte) {
+
+ idx++;
+ pte = pgtable[idx];
+ last_pte = pte + (PAGE_SIZE/sizeof(pte_t));
+ pgd++;
+
+ if (!*pgd) {
+ *pgd = (((int)pgtable[idx] - KERNEL_VIRT_ADDR) | pgd_flags);
+ }
+ }
+
+ *pte = (phys_addr | pte_flags);
+
+ pte++;
+ start += 0x1000;
+ phys_addr += 0x1000;
+ }
+}

page32.h

@@ -0,0 +1,29 @@
+/* File: page32.h */
+/* */
+/* Description: Header file for 32 bit page table handling code. */
+/* */
+/* Author: Shoily O Rahman <[email protected]> */
+/* */
+/* Date: July 9, 2020 */
+/* */
+/*****************************************************************************/
+
+#ifndef PAGE32_H
+#define PAGE32_H
+
+typedef int pte_t;
+typedef int pgd_t;
+
+#define PAGE_SIZE 4096
+
+#define PGD_PRESENT 1
+#define PGD_WRITE 2
+#define PGD_USER 4
+
+#define PTE_PRESENT 1
+#define PTE_WRITE 2
+#define PTE_USER 4
+
+void build_pagetable(pgd_t *pgdir, pte_t **pgtable, int phys_addr, int start, int length, int pgd_flags, int pte_flags);
+
+#endif