From edf9e71e2a7b6b89775c29cf28c19c6b89992c25 Mon Sep 17 00:00:00 2001 From: aqua Date: Mon, 28 Mar 2022 20:03:38 +0300 Subject: Initial commit x86 kernel that prints a hello world message to com1 --- arch/i686/boot.S | 89 ++++++++++++++++++++++++++++++++++++++++++++++ arch/i686/gdt.c | 20 +++++++++++ arch/i686/include/gdt.h | 60 +++++++++++++++++++++++++++++++ arch/i686/include/paging.h | 59 ++++++++++++++++++++++++++++++ arch/i686/include/sys/io.h | 79 ++++++++++++++++++++++++++++++++++++++++ arch/i686/init.s | 42 ++++++++++++++++++++++ arch/i686/lgdt.c | 31 ++++++++++++++++ arch/i686/linker.ld | 54 ++++++++++++++++++++++++++++ arch/i686/macros.s | 25 +++++++++++++ arch/i686/meson.build | 6 ++++ arch/i686/test/gdt.c | 20 +++++++++++ arch/i686/toolchain.ini | 18 ++++++++++ 12 files changed, 503 insertions(+) create mode 100644 arch/i686/boot.S create mode 100644 arch/i686/gdt.c create mode 100644 arch/i686/include/gdt.h create mode 100644 arch/i686/include/paging.h create mode 100644 arch/i686/include/sys/io.h create mode 100644 arch/i686/init.s create mode 100644 arch/i686/lgdt.c create mode 100644 arch/i686/linker.ld create mode 100644 arch/i686/macros.s create mode 100644 arch/i686/meson.build create mode 100644 arch/i686/test/gdt.c create mode 100644 arch/i686/toolchain.ini (limited to 'arch') diff --git a/arch/i686/boot.S b/arch/i686/boot.S new file mode 100644 index 0000000..1eea9a3 --- /dev/null +++ b/arch/i686/boot.S @@ -0,0 +1,89 @@ +#define ASM_FILE +#include +#include "macros.s" + +/* Declare a multiboot header that marks this program as a kernel */ +.section .multiboot.header, "a" +header_begin: +.align 8 + .int MULTIBOOT2_HEADER_MAGIC + .int MULTIBOOT_ARCHITECTURE_I386 + .int header_end - header_begin + .int -(MULTIBOOT2_HEADER_MAGIC + MULTIBOOT_ARCHITECTURE_I386 + (header_end - header_begin)) + +.align 8 +header_info_begin: + .short MULTIBOOT_HEADER_TAG_INFORMATION_REQUEST + .short 0 # flags + .int header_info_end - header_info_begin + .int MULTIBOOT_TAG_TYPE_MMAP +header_info_end: + +.align 8 + .short MULTIBOOT_HEADER_TAG_END + .short 0 + .int 8 +header_end: + +.section .multiboot.pages, "aw", @nobits +.align 4096 +bootstrap_page0: + .skip 1024 * 4 + +.section .multiboot.text, "ax" +.extern k_pagedir +.extern k_stack +.extern k_init + +#.global __vaddr_base +#.set __vaddr_base, 0xc0000000 +#.global __vaddr_offset +.set __vaddr_offset, 0xc0000000 - 0x2000 + +.global _start +.type _start, @function +_start: + cli + + # check multiboot header + cmp $MULTIBOOT2_BOOTLOADER_MAGIC, %eax + jz c + hlt + +c: mov $k_stack - __vaddr_offset, %esp + + push %ebx # pointer to multiboot structure + call __multiboot2 + + # mmap multiboot section into bootstrap page + movl $bootstrap_page0, %edi + movl $1024, %ecx + mmap_section __multiboot_begin, __multiboot_end, PAGE_RW + mmap_section (__text_begin - __vaddr_offset), (__text_end - __vaddr_offset), PAGE_RO + mmap_section (__rodata_begin - __vaddr_offset), (__rodata_end - __vaddr_offset), PAGE_RO + mmap_section (__bss_begin - __vaddr_offset), (__bss_end - __vaddr_offset), PAGE_RW + mmap_section (__data_begin - __vaddr_offset), (__data_end - __vaddr_offset), PAGE_RW + + # mmap all the other section into k_ptable0x300 + movl $(k_ptable0x300 - __vaddr_offset), %edi + movl $1024, %ecx + mmap_section (__text_begin - __vaddr_offset), (__text_end - __vaddr_offset), PAGE_RO + mmap_section (__rodata_begin - __vaddr_offset), (__rodata_end - __vaddr_offset), PAGE_RO + mmap_section (__bss_begin - __vaddr_offset), (__bss_end - __vaddr_offset), PAGE_RW + mmap_section (__data_begin - __vaddr_offset), (__data_end - __vaddr_offset), PAGE_RW + + movl $(bootstrap_page0 + PAGE_RW), k_pagedir - __vaddr_offset + 0 * 4 + movl $(k_ptable0x300 - __vaddr_offset + PAGE_RW), k_pagedir - __vaddr_offset + 768 * 4 + + movl $(k_pagedir - __vaddr_offset), %ecx + movl %ecx, %cr3 + + # enable paging and the write-protect bit + movl %cr0, %ecx + orl $0x80010000, %ecx + movl %ecx, %cr0 + + # jump to higher half with an absolute jump + lea (k_init), %ecx + jmp *%ecx + diff --git a/arch/i686/gdt.c b/arch/i686/gdt.c new file mode 100644 index 0000000..fe0bfc9 --- /dev/null +++ b/arch/i686/gdt.c @@ -0,0 +1,20 @@ +#include + +void +SegmentDescriptor(struct SegmentDescriptor_t *self, unsigned base, unsigned limit, uint8_t access) +{ + self->base_15_0 = base & 0xffff; + self->base_23_16 = (base >> 16) & 0xff; + self->base_31_24 = (base >> 24) & 0xff; + + self->limit_15_0 = (limit <= 0xffff) ? (limit & 0xffff) : ((limit >> 12) & 0xffff); + self->limit_19_16 = (limit <= 0xffff) ? 0 : ((limit >> 28) & 0xf); + + self->access = access; + + self->a = 0; + self->rsv = 0; + self->db = (limit > 0xffff) ? 1 : 0; + self->granularity = (limit > 0) ? 1 : 0; +} + diff --git a/arch/i686/include/gdt.h b/arch/i686/include/gdt.h new file mode 100644 index 0000000..6badf84 --- /dev/null +++ b/arch/i686/include/gdt.h @@ -0,0 +1,60 @@ +#pragma once + +#include +#include + +enum Ring { Ring0 = 0x0, Ring1 = 0x1, Ring2 = 0x2, Ring3 = 0x3 }; + +struct __attribute__((packed)) Access { + bool accessed : 1; // if 0, is set by processor when accessed + bool readwrite : 1; // code seg: read toggle; data seg: write toggle + bool direction : 1; // code seg: conforming bit; data seg: direction bit + bool executable : 1; // executable bit + bool segment : 1; // true for code/data; false for gates/tss + enum Ring privilege : 2; // descriptor privilege level + bool present : 1; // true for every active segment +}; +_Static_assert(sizeof(struct Access) == 1); + +static const struct Access null_access = {}; +static const struct Access ktext_access = {.readwrite = true, .executable = true, .segment = true, .present = true}; +static const struct Access kdata_access = {.readwrite = true, .segment = true, .present = true}; + +// Segment Descriptor +// A memory structure (part of a table) that tells the CPU the attributes of a given segment +// |31| | | | | | |24|23|22|21|20|19| | |16|15| | | | | | | 8| 7| | | | | | | 0| +// | base_31_24 | G|DB| | A| lim_19_16 | access | base_23_16 | +// | base_15_0 | limit_15_0 | +// |31| | | | | | | | | | | | | | |16|15| | | | | | | | | | | | | | | 0| +// limit size of segment - 1, either in bytes or in 4KiB chunks (check flags) +// base address of segment +// access +// flags defines the segment chunks and 16/32 bit +struct __attribute__((packed)) SegmentDescriptor_t { + uint16_t limit_15_0; // low bits of segment limit + uint16_t base_15_0; // low bits of segment base address + uint8_t base_23_16; // middle bits of segment base address + uint8_t access; // access byte + uint8_t limit_19_16 : 4; // high bits of segment limit + // flags + bool a : 1; // unused, available for software use + bool rsv : 1; // reserved + bool db : 1; // false => 16-bit seg; true => 32-bit seg + bool granularity : 1; // limit scaled by 4k when set + uint8_t base_31_24; // high bits of segment address +}; +_Static_assert(sizeof(struct SegmentDescriptor_t) == 8); + +void SegmentDescriptor(struct SegmentDescriptor_t *self, unsigned base, unsigned limit, uint8_t access); + +struct __attribute__((packed)) Pointer { + uint16_t limit; + uint32_t base; +}; + +void gdt_install(); + +enum SegmentIndex { + ktextDescriptor = 2 * sizeof(struct SegmentDescriptor_t), + kdataDescriptor = 3 * sizeof(struct SegmentDescriptor_t), +}; diff --git a/arch/i686/include/paging.h b/arch/i686/include/paging.h new file mode 100644 index 0000000..cff0506 --- /dev/null +++ b/arch/i686/include/paging.h @@ -0,0 +1,59 @@ +#pragma once + +// DirectoryEntry +// |31| | | | | | | | | | | | | | | | | | | |11| | 9| 8| 7| 6| 5| 4| 3| 2| 1| 0| +// | page table 4-kb aligned address | avail | G| S| | A| C| W| U| R| P| +struct __attribute__((packed)) DirectoryEntry { + unsigned present : 1; // 0: if set, the page is actually in physical memory + unsigned writeable : 1; // 1: if set, the page is read/write; otherwise the page is read-only + unsigned user : 1; // 2: if set, then page can be access by all; otherwise only the supervisor can access it + unsigned writethrough : 1; // 3: if set, write-through caching is enabled; otherwise write-back is enabled instead + unsigned cachedisable : 1; // 4: if set, the page will not be cached + unsigned accessed : 1; // 5: set by the CPU when the page is read from or written to + unsigned dirty : 1; // 6: used to determine whether a page has been written to + unsigned pagesize : 1; // 7: page size == 0 + unsigned global : 1; + unsigned int __available__ : 3; // available to the OS + unsigned int address : 20; +}; +_Static_assert(sizeof(struct DirectoryEntry) == 4); + +// DirectoryEntry4MB +// |31| | | | | | | | |22|21|20| | | | | | |13|12|11| | 9| 8| 7| 6| 5| 4| 3| 2| 1| 0| +// | bits 31-22 of address |RS| bits 39-22 of |AT| avail | G|PS| D| A|CD|WT|US|RW| P| +// | |VD| address +struct __attribute__((packed)) DirectoryEntry4MB { + unsigned present : 1; // 0: if set, the page is actually in physical memory + unsigned writeable : 1; // 1: if set, the page is read/write; otherwise the page is read-only + unsigned useraccess : 1; // 2: if set, then page can be access by all; otherwise only the supervisor can access it + unsigned writethrough : 1; // 3: if set, write-through caching is enabled; otherwise write-back is enabled instead + unsigned cachedisable : 1; // 4: if set, the page will not be cached + unsigned accessed : 1; // 5: set by the CPU when the page is read from or written to + unsigned dirty : 1; // 6: used to determine whether a page has been written to + unsigned pagesize : 1; // 7: page size == 1 + unsigned global : 1; // 8: + unsigned __available__ : 3; // 11..9 available to the OS + unsigned pat : 1; // 12: page attribute table + unsigned int address_high : 8; + unsigned rsvd : 1; // 21 + unsigned int address_low : 10; +}; +_Static_assert(sizeof(struct DirectoryEntry4MB) == 4); + +// TableEntry +// |31| | | | | | | | | | | | | | | | | | | |11| | 9| 8| 7| 6| 5| 4| 3| 2| 1| 0| +// | page table 4-kb aligned address | avail | G| | D| A| C| W|US|RW| P| +struct __attribute__((packed)) TableEntry { + unsigned present : 1; // if set, the page is actually in physical memory + unsigned writeable : 1; // if set, the page is read/write; otherwise the page is read-only + unsigned user : 1; // if set, then page can be access by all; otherwise only the supervisor can access it + unsigned writethrough : 1; // if set, write-through caching is enabled; otherwise write-back is enabled instead + unsigned cachedisable : 1; // if set, the page will not be cached + unsigned accessed : 1; // set by the CPU when the page is read from or written to + unsigned dirty : 1; // used to determine whether a page has been written to + unsigned pat : 1; // page attribute table? + unsigned global : 1; + unsigned int __available__ : 3; // available to the OS + unsigned int address : 20; +}; +_Static_assert(sizeof(struct TableEntry) == 4); diff --git a/arch/i686/include/sys/io.h b/arch/i686/include/sys/io.h new file mode 100644 index 0000000..74d4950 --- /dev/null +++ b/arch/i686/include/sys/io.h @@ -0,0 +1,79 @@ +#pragma once + +static inline void +outb(unsigned char val, unsigned short port) +{ + asm volatile("outb %0,%1" : : "a"(val), "dN"(port)); +} + +static inline void +outw(unsigned short val, unsigned short port) +{ + asm volatile("outw %0,%1" : : "a"(val), "dN"(port)); +} + +static inline void +outl(unsigned int val, unsigned short port) +{ + asm volatile("outl %0,%1" : : "a"(val), "dN"(port)); +} + +static inline unsigned char +inb(unsigned short port) +{ + unsigned char val; + asm volatile("inb %1,%0" : "=a"(val) : "dN"(port)); + return val; +} + +static inline unsigned short +inw(unsigned short port) +{ + unsigned short val; + asm volatile("inw %1,%0" : "=a"(val) : "dN"(port)); + return val; +} + +static inline unsigned int +inl(unsigned short port) +{ + unsigned int val; + asm volatile("inl %1,%0" : "=a"(val) : "dN"(port)); + return val; +} + +static inline void +outsb(unsigned short port, const void *__buf, unsigned long __n) +{ + asm volatile("cld; rep; outsb" : "+S"(__buf), "+c"(__n) : "d"(port)); +} + +static inline void +outsw(unsigned short port, const void *__buf, unsigned long __n) +{ + asm volatile("cld; rep; outsw" : "+S"(__buf), "+c"(__n) : "d"(port)); +} + +static inline void +outsl(unsigned short port, const void *__buf, unsigned long __n) +{ + asm volatile("cld; rep; outsl" : "+S"(__buf), "+c"(__n) : "d"(port)); +} + +static inline void +insb(unsigned short port, void *__buf, unsigned long __n) +{ + asm volatile("cld; rep; insb" : "+D"(__buf), "+c"(__n) : "d"(port)); +} + +static inline void +insw(unsigned short port, void *__buf, unsigned long __n) +{ + asm volatile("cld; rep; insw" : "+D"(__buf), "+c"(__n) : "d"(port)); +} + +static inline void +insl(unsigned short port, void *__buf, unsigned long __n) +{ + asm volatile("cld; rep; insl" : "+D"(__buf), "+c"(__n) : "d"(port)); +} diff --git a/arch/i686/init.s b/arch/i686/init.s new file mode 100644 index 0000000..92710df --- /dev/null +++ b/arch/i686/init.s @@ -0,0 +1,42 @@ +.section .stack, "aw", @nobits +.global k_stack +.align 16 /* Stack on x86 must be 16-byte aligned according to System V ABI */ +k_stack_bottom: + .skip 16 * 1024 /* 16 kByte */ +k_stack: + +.section .pages, "aw", @nobits +.align 4096 +.global k_pagedir +k_pagedir: .skip 1024 * 4 +.global k_ptable0x300 +k_ptable0x300: .skip 1024 * 4 + +.section .text +.global k_init +.extern kmain +k_init: + # kernel entry point, higher half + + # unmap the identity mapping as its no longer necessary + movl $0, k_pagedir + 0 * 4 + mov %cr3, %ecx # reload cr3 to force a TLB flush + mov %ecx, %cr3 + + # zero out the stack + mov $4096, %ecx # loop counter + mov $k_stack_bottom, %edi # start from the bottom + xor %edx, %edx # clear %edx +1: movl %edx, (%edi) # store %edx into address in %edi + addl $4, %edi # point to next address + loop 1b # loop according to %ecx + + mov $k_stack, %esp # point stack pointer to the stack + + call kmain + + /* If the system has nothing more to do, put it in an infinite loop */ + cli # disable interrupts +h: hlt # wait for interrupt + jmp h # continue waiting for interrupt + diff --git a/arch/i686/lgdt.c b/arch/i686/lgdt.c new file mode 100644 index 0000000..2d35e8d --- /dev/null +++ b/arch/i686/lgdt.c @@ -0,0 +1,31 @@ +#include + +static struct SegmentDescriptor_t segments[8] __attribute__((aligned(32))); + +void +gdt_install() +{ + SegmentDescriptor(&segments[0], 0, 0, 0); // null segment + SegmentDescriptor(&segments[2], 0, 0xffffffff, 0x9a); // ktext + SegmentDescriptor(&segments[3], 0, 0xffffffff, 0x92); // kdata + + struct Pointer ptr = {.limit = sizeof(segments) - 1, .base = (unsigned)&segments}; + + asm volatile("lgdt (%0)" : : "a"(&ptr)); + + // load the kernel data segment + asm volatile(R"(mov %0, %%ds + mov %0, %%es + mov %0, %%fs + mov %0, %%gs + mov %0, %%ss +)" + : + : "ax"(kdataDescriptor)); + + // load the kernel code segment + asm volatile(R"(ljmp %0, $1f + 1:)" + : + : "i"(ktextDescriptor)); +} diff --git a/arch/i686/linker.ld b/arch/i686/linker.ld new file mode 100644 index 0000000..61a3be9 --- /dev/null +++ b/arch/i686/linker.ld @@ -0,0 +1,54 @@ +ENTRY(_start) +OUTPUT_FORMAT(elf32-i386) + +MULTIBOOT_SIZE = 0x2000; +VADDR_BASE = 0xc0000000; + +SECTIONS +{ + /* First put the multiboot header, as it is required to be put very early in the image or the bootloader won't * + * recognize the file format. * + * Once the MMU is set up, this section is no longer needed and should be unmapped. */ + . = 0; + .bootstrap : { + . = ALIGN(8); + __multiboot_begin = .; + KEEP(*(.multiboot.header)) + KEEP(*(.multiboot.text)) + KEEP(*(.multiboot.pages)) + __multiboot_end = .; + } + + . = VADDR_BASE; + + .text ALIGN(4K) : AT(ADDR(.text) - VADDR_BASE + MULTIBOOT_SIZE) { + __text_begin = .; + *(.text*) + __text_end = .; + } + + /* Read-only data. */ + .rodata ALIGN(4K) : AT(ADDR(.rodata) - VADDR_BASE + MULTIBOOT_SIZE) { + __rodata_begin = .; + *(.constinit) + *(.rodata*) + __rodata_end = .; + } + + /* Read-write data (uninitialized) and stack */ + .bss ALIGN(4K) : AT(ADDR(.bss) - VADDR_BASE + MULTIBOOT_SIZE) { + __bss_begin = .; + *(.stack) + *(.pages) + *(.bss*) + __bss_end = .; + } + + /* Read-write data (initialized) */ + .data ALIGN(4K) : AT(ADDR(.data) - VADDR_BASE + MULTIBOOT_SIZE) { + __data_begin = .; + *(.init) + *(.data) + __data_end = .; + } +} diff --git a/arch/i686/macros.s b/arch/i686/macros.s new file mode 100644 index 0000000..a9b8b4d --- /dev/null +++ b/arch/i686/macros.s @@ -0,0 +1,25 @@ +.set PAGE_RO, 0x001 +.set PAGE_RW, 0x003 +/* write section to page table macro + * + * Registers used: + * %ecx: loop counter [ set to $1024 ] + * %edx: temporary + * %esi: current page being mapped + * %edi: page entry [ set to $page_addr ] + */ +.macro mmap_section begin, end, access + mov $\begin, %esi # from $begin +1: cmpl $\end, %esi # until $end + jge 2f + + movl %esi, %edx + orl $\access, %edx + movl %edx, (%edi) + + addl $4096, %esi # move to next page + addl $4, %edi # size of page entry is 4 bytes + loop 1b # loop according to %ecx +2: +.endm + diff --git a/arch/i686/meson.build b/arch/i686/meson.build new file mode 100644 index 0000000..25eebee --- /dev/null +++ b/arch/i686/meson.build @@ -0,0 +1,6 @@ +arch = declare_dependency( + sources: ['boot.S', 'init.s', 'gdt.c', 'lgdt.c'], + include_directories: 'include' +) + +test('GDT', executable('gdt', ['test/gdt.c', 'gdt.c'], include_directories: 'include', native: true)) diff --git a/arch/i686/test/gdt.c b/arch/i686/test/gdt.c new file mode 100644 index 0000000..2947b42 --- /dev/null +++ b/arch/i686/test/gdt.c @@ -0,0 +1,20 @@ +#include "gdt.h" +#include +#include + +int +main() +{ + assert(*(uint8_t *)&null_access == 0x00); + assert(*(uint8_t *)&ktext_access == 0x9a); + assert(*(uint8_t *)&kdata_access == 0x92); + + struct SegmentDescriptor_t d; + SegmentDescriptor(&d, 0, 0, 0); + assert(*(uint64_t *)&d == 0); + + assert(ktextDescriptor == 0x10); + assert(kdataDescriptor == 0x18); + + return EXIT_SUCCESS; +} diff --git a/arch/i686/toolchain.ini b/arch/i686/toolchain.ini new file mode 100644 index 0000000..6f6b5ef --- /dev/null +++ b/arch/i686/toolchain.ini @@ -0,0 +1,18 @@ +[constants] +arch = 'i686' + +[host_machine] +system = 'none' +cpu_family = 'x86' +cpu = 'i686' +endian = 'little' + +[binaries] +c = 'i686-elf-gcc' +ar = 'i686-elf-ar' +strip = 'i686-elf-strip' + +[built-in options] +c_args = ['-fanalyzer', '-ffreestanding'] +c_link_args = [ '-static', '-nostdlib', '-T', 'arch/i686/linker.ld' ] + -- cgit v1.2.1