mirror of
https://github.com/originalmk/mkos32.git
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Non-flat segmentation set from C
Playing with non-flat segmentation, but it seems that it won't be feasible to use it with C programs - implementing paging and flat segmentation scheme will be neceassary.
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4fc60d7440
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56
boot.s
56
boot.s
@ -29,17 +29,14 @@
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.section .bss
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.align 16
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.global stack_top
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.global stack_bottom
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stack_bottom:
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/* Stos o wielkości 16 KB */
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.skip 16834
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.skip 16384
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stack_top:
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.section .data
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/* 31, bo będą 4 deskryptory po 8 bajtów, a przekazujemy wielkość - 1*/
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// TODO
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gdtr: .word 23
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/* Na 4 MiB daję bazę dla GDT, czyli tam gdzie zaczynają się dane kernela */
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gdtb: .long 0x400000
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/*
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Oznaczenie startu, tu zaczyna się kod kernela!
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@ -48,48 +45,23 @@ gdtb: .long 0x400000
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.global _start
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.type _start, @function
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_start:
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/* Tutaj podobno jest tryb chroniony już, jednak zastanawia czy faktycznie
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* bootloader ustawia za nas segmentacje pamięci?
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* EDIT: Ustawia, ale pod własne potrzeby, więc i tak trzeba zmienić
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* Ustawię zatem najprostszy model segmentacji */
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// Domyślne ustawienia z GRUB-a są takie, że pomijają segmentację!
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// Dodam w ramach segmentu danych kernela, czyli u mnie 4-8 MiB
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mov gdtb, %eax
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// 1. Pusty (null) deskryptor
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movl $0, (%eax)
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movl $0, 4(%eax)
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// 2. Deskryptor kodu jądra
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movl $0x000003FF, 8(%eax)
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movl $0x00c09800, 12(%eax)
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// 3. Deskryptor danych jądra
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movl $0x000003FF, 16(%eax)
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movl $0x00C09240, 20(%eax)
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// 4. Deskryptor kodu użytkownika
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// 6. Load GDT
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lgdt (gdtr)
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// 7. Refresh registers
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mov %cs, 8(%eax)
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mov %ds, 16(%eax)
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mov %es, 16(%eax)
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mov %fs, 16(%eax)
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mov %gs, 16(%eax)
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mov %ss, 16(%eax)
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// Wpisywane jest i tak pod %ds:64
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movb $69, (64)
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/* Ustawienie ESP na wierzchołek stosu */
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mov $stack_top, %esp
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/* Tutaj jakieś ustawienia inicjalizacyjne trzeba zrobić normalnie */
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//mov $69, %esi
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//mov $_start, %edi
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/* Wywołanie kernela */
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call kernel_main
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mov $0x10, %ax
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mov %ax, %ds
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mov %ax, %es
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mov %ax, %fs
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mov %ax, %gs
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mov %ax, %ss
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jmp $0x08,$cs_refresh
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cs_refresh:
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mov $0x4000, %esp
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push $5
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/* Wieczne oczekiwanie po zakończeniu kodu kernela */
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cli
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1: hlt
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120
kernel.c
120
kernel.c
@ -164,24 +164,45 @@ void terminal_write(const char *data, size_t size)
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}
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}
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void terminal_writenum(uint64_t number, int base)
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// Pad length is what number length should be, including padding
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void terminal_writenumpad(uint64_t number, int base, int pad_length)
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{
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char digits[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
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size_t size = 0;
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int size = 0;
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char numChars[32];
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while (number != 0)
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if (number == 0)
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{
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uint64_t rest = number / base;
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uint64_t digit = number % base;
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numChars[31] = '0';
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size = 1;
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}
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else
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{
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while (number != 0)
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{
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uint64_t rest = number / base;
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uint64_t digit = number % base;
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numChars[31 - size++] = digits[digit];
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number = rest;
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numChars[31 - size++] = digits[digit];
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number = rest;
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}
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}
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// Write pad_length - size of zeros
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// If padding won't be needed (number is longer than pad_legnth)
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// then loop won't run at all
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while (pad_length > size) {
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numChars[31 - size++] = digits[0];
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}
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terminal_write(numChars + (32 - size), size);
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}
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void terminal_writenum(uint64_t number, int base)
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{
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terminal_writenumpad(number, base, 0);
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}
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void terminal_writestring(const char *data)
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{
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terminal_write(data, strlen(data));
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@ -230,7 +251,7 @@ struct gdt_entry {
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#define KERNEL_SEGMENT 0
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#define USER_SEGMENT 1
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#define CODE_SEGMENT 0
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#define USER_SEGMENT 1
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#define DATA_SEGMENT 1
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struct gdt_entry gdt_entry_create(size_t start_address, size_t pages_size,
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int kernel_or_user, int code_or_data)
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@ -276,11 +297,13 @@ struct gdt_entry gdt_entry_create(size_t start_address, size_t pages_size,
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// F = G DB L -
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uint64_t gdt_entry_encode(struct gdt_entry entry)
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{
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entry.base = entry.base << 12;
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uint64_t gdt_encoded = 0;
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// Insert base
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gdt_encoded |= ((uint64_t) (entry.base & 0xFF000000) << 32);
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gdt_encoded |= ((uint64_t) (entry.base & 0x00FFFFFF) << 16);
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gdt_encoded |= ((((uint64_t) entry.base) & 0xFF000000) << 32);
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gdt_encoded |= ((((uint64_t) entry.base) & 0x00FFFFFF) << 16);
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// Insert limit
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gdt_encoded |= ((uint64_t) (entry.limit & 0xF0000) << 32);
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@ -306,14 +329,15 @@ uint64_t gdt_entry_encode(struct gdt_entry entry)
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access_byte |= entry.was_accessed;
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// Insert access byte
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gdt_encoded |= (access_byte << 20);
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gdt_encoded |= (access_byte << 40);
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return gdt_encoded;
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}
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struct gdt_table {
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uint16_t entries_count;
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uint32_t *dest_pointer;
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struct __attribute__((__packed__)) gdt_table
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{
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uint16_t size_in_bytes;
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uint64_t *dest_pointer;
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struct gdt_entry entries[16];
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};
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@ -323,26 +347,19 @@ void apply_table(struct gdt_table table)
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uint64_t null_entry_encoded = 0;
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*table.dest_pointer = null_entry_encoded;
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for (int i = 0; i < table.entries_count; i++)
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int entries_count = (table.size_in_bytes + 1) / 8;
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for (int i = 0; i < entries_count; i++)
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{
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uint64_t entry_encoded = gdt_entry_encode(table.entries[i]);
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uint32_t *dest_address = table.dest_pointer + (i + 1) * 8;
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uint64_t *dest_address = table.dest_pointer + i + 1;
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*dest_address = entry_encoded;
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}
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__asm__("lgdt (%0)" : : "r" (&table));
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}
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void kernel_main(void)
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void print_texts()
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{
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/*
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* Initialize terminal interface
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*/
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terminal_initialize();
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/*
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* Newline support is left as an exercise.
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*/
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terminal_writestring("TEGO NIE POWINNO BYC WIDAC\n");
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terminal_writestring
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("Witam i pozdrawiam, MK\nTest wielolinijkowosci\n");
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@ -374,11 +391,50 @@ void kernel_main(void)
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size_t human_readable = start_point / (1024 * 1024);
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terminal_writenum(human_readable, 10);
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terminal_writestring(" MiB\n");
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terminal_writestring("Test wpisu GDT:\n");
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struct gdt_entry entry =
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gdt_entry_create(0, 0x400, KERNEL_SEGMENT, CODE_SEGMENT);
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uint64_t entry_encoded = gdt_entry_encode(entry);
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terminal_writenum(entry_encoded, 16);
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terminal_newline();
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}
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void gdt_setup()
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{
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struct gdt_entry kernel_code_entry =
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gdt_entry_create(0, 0x400, KERNEL_SEGMENT, CODE_SEGMENT);
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struct gdt_entry kernel_data_entry =
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gdt_entry_create(0x400, 0x400, KERNEL_SEGMENT, DATA_SEGMENT);
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struct gdt_entry user_code_entry =
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gdt_entry_create(0x800, 0x400, USER_SEGMENT, CODE_SEGMENT);
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struct gdt_entry user_data_entry =
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gdt_entry_create(0xC00, 0x400, USER_SEGMENT, DATA_SEGMENT);
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struct gdt_table gdt_table;
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gdt_table.size_in_bytes = 39;
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gdt_table.dest_pointer = (uint64_t*)0x400000;
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gdt_table.entries[0] = kernel_code_entry;
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gdt_table.entries[1] = kernel_data_entry;
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gdt_table.entries[2] = user_code_entry;
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gdt_table.entries[3] = user_data_entry;
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apply_table(gdt_table);
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terminal_writestring("GDT table applied\n");
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__asm__ volatile(
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"mov $stack_bottom, %%esi;"
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"mov $0x500000, %%edi;"
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"mov $16384, %%ecx;"
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"cld;"
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"rep movsb;"
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:
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:
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:
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"esi","edi","ecx"
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);
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__asm__(
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"xchg %bx, %bx"
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);
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}
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void kernel_main(void)
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{
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terminal_initialize();
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print_texts();
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gdt_setup();
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}
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