From da4e7bf5dd2b9448b638255a20ee503b0641e495 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Duje=20Mihanovi=C4=87?= Date: Tue, 21 Jun 2022 20:40:37 +0200 Subject: [PATCH] Load ELF kernel instead of flat binary Also moves most of the protected mode portion of the bootloader to a C environment rather than assembly. --- .gitignore | 3 -- Makefile | 17 ++++---- boot/x86/Makefile | 10 ++--- boot/x86/stage3/elf.c | 78 +++++++++++++++++++++++++++++++++++++ boot/x86/stage3/elf.h | 60 ++++++++++++++++++++++++++++ boot/x86/stage3/loader.s | 55 +++++++------------------- boot/x86/stage3/paging.c | 7 +--- boot/x86/stage3/paging.h | 13 +++++++ boot/x86/stage3/prekernel.c | 62 +++++++++++++++++++++++++++++ kernel/entry.s | 23 ++++++++++- kernel/linker.ld | 1 - nameless2disk | 4 +- 12 files changed, 263 insertions(+), 70 deletions(-) create mode 100644 boot/x86/stage3/elf.c create mode 100644 boot/x86/stage3/elf.h create mode 100644 boot/x86/stage3/paging.h create mode 100644 boot/x86/stage3/prekernel.c diff --git a/.gitignore b/.gitignore index 9fc5bb7..505290e 100644 --- a/.gitignore +++ b/.gitignore @@ -1,6 +1,3 @@ -toolchain/ -boot.img -boot/x86/boot **/*.o **/*.bin **/*.elf diff --git a/Makefile b/Makefile index 714528a..f254d0c 100644 --- a/Makefile +++ b/Makefile @@ -25,34 +25,31 @@ debug: all boot/x86/mbr: boot/x86/mbr.s boot/x86/vbr-fat32: boot/x86/vbr-fat32.s boot/x86/fat32/*.s -boot/x86/stage3/LOADER.BIN: boot/x86/stage3/*.s boot/x86/stage3/*.c boot/x86/fat32/*.s -boot/x86/stage3/loader.elf: boot/x86/stage3/*.s boot/x86/stage3/*.c boot/x86/fat32/*.s +boot/x86/stage3/LOADER.BIN: boot/x86/stage3/*.s boot/x86/stage3/*.c boot/x86/fat32/*.s boot/x86/stage3/stage3.ld +boot/x86/stage3/loader.elf: boot/x86/stage3/*.s boot/x86/stage3/*.c boot/x86/fat32/*.s boot/x86/stage3/stage3.ld $(BOOTLOADER_OBJ): $(MAKE) -C boot/x86 -boot/x86/disk.img: boot/x86/mbr boot/x86/vbr-fat32 boot/x86/stage3/LOADER.BIN boot/x86/disk.dump kernel/kernel.bin +boot/x86/disk.img: boot/x86/mbr boot/x86/vbr-fat32 boot/x86/stage3/LOADER.BIN boot/x86/disk.dump kernel/kernel.elf truncate -s1G boot/x86/disk.img sfdisk boot/x86/disk.img < boot/x86/disk.dump mkfs.fat -F 32 --offset 2048 boot/x86/disk.img dd if=boot/x86/mbr of=boot/x86/disk.img bs=440 count=1 conv=notrunc dd if=boot/x86/vbr-fat32 of=boot/x86/disk.img bs=1 skip=90 seek=1048666 conv=notrunc mcopy -i boot/x86/disk.img@@1M boot/x86/stage3/LOADER.BIN ::. - mcopy -i boot/x86/disk.img@@1M kernel/kernel.bin ::./KERNEL.BIN - -kernel/kernel.bin: ${KERNEL_OBJ} kernel/linker.ld - $(CC) -ffreestanding -nostdlib -o $@ -T kernel/linker.ld ${KERNEL_OBJ} + mcopy -i boot/x86/disk.img@@1M kernel/kernel.elf ::./KERNEL.ELF kernel/arch/x86/irq/sample_handler.o: kernel/arch/x86/irq/sample_handler.c $(CC) $(CFLAGS) -mgeneral-regs-only -c $< -o $@ -kernel/kernel.elf: kernel/kernel.bin - $(CC) -ffreestanding -nostdlib -o $@ -T kernel/linker.ld ${KERNEL_OBJ} -Wl,--oformat=elf32-i386 +kernel/kernel.elf: $(KERNEL_OBJ) + $(CC) -ffreestanding -nostdlib -o $@ -T kernel/linker.ld ${KERNEL_OBJ} -lgcc i686-elf-objcopy --only-keep-debug kernel/kernel.elf kernel/kernel.dbg i686-elf-objcopy --add-gnu-debuglink=kernel/kernel.dbg kernel/kernel.elf i686-elf-strip --strip-unneeded kernel/kernel.elf clean: - -rm kernel/kernel.{bin,dbg,elf} ${KERNEL_OBJ} + -rm kernel/kernel.{dbg,elf} ${KERNEL_OBJ} cd boot/x86 && $(MAKE) clean .PHONY: default all clean run debug bootloader diff --git a/boot/x86/Makefile b/boot/x86/Makefile index a5bad92..e75e8dc 100644 --- a/boot/x86/Makefile +++ b/boot/x86/Makefile @@ -1,10 +1,10 @@ default: mbr vbr-fat32 stage3/LOADER.BIN stage3/loader.elf -CFLAGS=-g -ffreestanding +CFLAGS=-g -ffreestanding -Istage3 LD=i686-elf-gcc -LDFLAGS=-T stage3/stage3.ld -nostdlib -g +LDFLAGS=-T stage3/stage3.ld -ffreestanding -nostdlib -g -STAGE3_OBJ=stage3/loader.o stage3/paging.o +STAGE3_OBJ=stage3/loader.o stage3/paging.o stage3/elf.o stage3/prekernel.o mbr: mbr.s $(AS) $(ASFLAGS) -w-zeroing -o $@ $< @@ -13,10 +13,10 @@ vbr-fat32: vbr-fat32.s fat32/*.s $(AS) $(ASFLAGS) -o $@ $< stage3/loader.elf: $(STAGE3_OBJ) - $(CC) $(LDFLAGS) -o $@ $^ -Wl,--oformat=elf32-i386 + $(CC) $(LDFLAGS) -o $@ $^ -lgcc -Wl,--oformat=elf32-i386 stage3/LOADER.BIN: $(STAGE3_OBJ) - $(CC) $(LDFLAGS) -o $@ $^ + $(CC) $(LDFLAGS) -o $@ $^ -lgcc stage3/loader.o: stage3/loader.s stage3/*.s $(AS) $(ASFLAGS) -f elf -g dwarf2 -DGIT_REVISION=\"$(GIT_REV)\" -o $@ $< diff --git a/boot/x86/stage3/elf.c b/boot/x86/stage3/elf.c new file mode 100644 index 0000000..d3d215f --- /dev/null +++ b/boot/x86/stage3/elf.c @@ -0,0 +1,78 @@ +/* Code for parsing ELF binaries (the kernel) */ + +#include +#include +#include + +int check_elf_header(struct elf_header *header) +{ + if (header->magic != ELF_MAGIC) + return ELF_HEADER_INVALID; + if (header->bits != ELF_32BIT) + return MISMATCHED_SYSTEM; + if (header->endianness != ELF_LITTLE_ENDIAN) + return MISMATCHED_SYSTEM; + if (header->header_ver != 1) + return ELF_HEADER_INVALID; + if (header->os_abi != ELF_SYSV_ABI) + return MISMATCHED_SYSTEM; + if (header->type != ELF_TYPE_EXECUTABLE) + return NOT_EXECUTABLE; + if (header->machine != ELF_X86_ISA) + return MISMATCHED_SYSTEM; + if (header->elf_ver != 1) + return ELF_HEADER_INVALID; + + return 0; +} + +int setup_elf_executable(struct elf_header *header) +{ + /* Check the header. */ + int header_valid = check_elf_header(header); + if (header_valid) + return header_valid; + + /* Get the program header. The casting is necessary because without it + * the code will add some multiple of the program header offset rather + * than the actual offset. */ + struct program_header *prog_hdr = (struct program_header *) ((uint32_t) header+header->program_hdr); + for (int i=0; iph_entry_count; i++) { + /* We're only interested in loadable segments. */ + if (prog_hdr[i].seg_type != ELF_PT_LOAD) + continue; + + /* Calculate the memory range. */ + void *phys_start, *phys_end, *virt_end; + int flags; + phys_start = (void *) header + prog_hdr[i].file_offset; + if (prog_hdr[i].memsz & 0xfff) { /* Align if needed. */ + phys_end = phys_start+((prog_hdr[i].memsz+0x1000) & ~0xfff); + virt_end = prog_hdr[i].vaddr+((prog_hdr[i].memsz+0x1000) & ~0xfff); + } + else { + phys_end = phys_start+prog_hdr[i].memsz; + virt_end = prog_hdr[i].vaddr+prog_hdr[i].memsz; + } + + flags = prog_hdr[i].flags & ELF_FLAG_WRITABLE; + + /* Map the range. */ + int ret = map_range(phys_start, phys_end, prog_hdr[i].vaddr, virt_end, flags); + if (ret) + return ret; + } + + return 0; +} + +int execute_elf(struct elf_header *header, void *arg1, int arg2) +{ + /* Check the header and map all needed memory ranges. */ + int ret = setup_elf_executable(header); + if (ret) + return ret; + + /* Execute the kernel. */ + header->entry(arg1, arg2); +} diff --git a/boot/x86/stage3/elf.h b/boot/x86/stage3/elf.h new file mode 100644 index 0000000..9692633 --- /dev/null +++ b/boot/x86/stage3/elf.h @@ -0,0 +1,60 @@ +#ifndef BOOT_X86_ELF_H +#define BOOT_X86_ELF_H + +#include + +/* Some constants we will test against. */ +#define ELF_MAGIC 0x464c457f +#define ELF_32BIT 0x1 +#define ELF_LITTLE_ENDIAN 0x1 +#define ELF_SYSV_ABI 0x0 +#define ELF_TYPE_EXECUTABLE 0x2 +#define ELF_X86_ISA 0x3 + +#define ELF_PT_LOAD 0x1 + +#define ELF_FLAG_EXECUTABLE 0x1 +#define ELF_FLAG_WRITABLE 0x2 +#define ELF_FLAG_READABLE 0x4 + +/* Return error codes for the functions. */ +#define ELF_HEADER_INVALID 5 +#define MISMATCHED_SYSTEM 6 +#define NOT_EXECUTABLE 7 + +struct elf_header { + uint32_t magic; + uint8_t bits; + uint8_t endianness; + uint8_t header_ver; /* always 1 */ + uint8_t os_abi; + uint8_t padding[8]; + uint16_t type; + uint16_t machine; + uint32_t elf_ver; /* always 1 */ + void (*entry)(void *, int); + uint32_t program_hdr; /* offset into file */ + uint32_t section_hdr; + uint32_t flags; + uint16_t hdr_size; + uint16_t ph_entry_size; + uint16_t ph_entry_count; + uint16_t sh_entry_size; + uint16_t sh_entry_count; + uint16_t sh_name_index; +}; + +struct program_header { + uint32_t seg_type; + uint32_t file_offset; + void *vaddr; + uint32_t undefined; + uint32_t filesz; + uint32_t memsz; + uint32_t flags; + uint32_t align; +}; + +extern int execute_elf(struct elf_header *header, void *arg1, int arg2); + +#endif diff --git a/boot/x86/stage3/loader.s b/boot/x86/stage3/loader.s index 9ed7102..87598f4 100644 --- a/boot/x86/stage3/loader.s +++ b/boot/x86/stage3/loader.s @@ -1,9 +1,7 @@ bits 16 cpu 686 -extern enable_paging -extern map_range -extern set_up_page_directory +extern run_kernel section .text %include "../fat32/fat32-structs.s" @@ -63,9 +61,11 @@ _start: pop si pop cx print kernel_found + mov eax, [es:di+dir_entry.filesize] + mov [KERNEL_SIZE], eax mov ax, [es:di+dir_entry.firstclushi] shl eax, 16 - mov ax, [es:di+(dir_entry.firstcluslo)] + mov ax, [es:di+dir_entry.firstcluslo] call print_dword mov edi, 0x100000 print kernel_loading @@ -177,47 +177,18 @@ in_protected: mov fs, ax mov gs, ax - push dword 0 - push 0xc0003000 - push 0xc0000000 - push 0x103000 + push dword [KERNEL_SIZE] push 0x100000 - call map_range - cmp eax, 0 - jne .error - add esp, 20 - push dword 2 - push 0xc0009000 - push 0xc0003000 - push 0x109000 - push 0x103000 - call map_range - cmp eax, 0 - jne .error - add esp, 20 - push dword 2 - push 0x100000 - push dword 0 - push 0x100000 - push dword 0 - call map_range - cmp eax, 0 - jne .error - add esp, 20 - - call set_up_page_directory - call enable_paging - - jmp 0xc0000000 - nop -.error: - mov dword [0xb8000], 0xcf28cf3a - hlt - jmp $-1 + push ebx + push edi + call run_kernel + +section .bss +KERNEL_SIZE: resd 1 section .rodata -kernel_name: db "KERNEL BIN" +kernel_name: db "KERNEL ELF" begin: db "Nameless Bootloader revision ", GIT_REVISION, 0xd, 0xa, 0 a20_enabled: db "A20 has been enabled", 0xd, 0xa, "Searching for kernel...", 0xd, 0xa, 0 a20_fail: db "Failed to enable A20, giving up!", 0xd, 0xa, 0 @@ -225,7 +196,7 @@ crit_err: db "A critical error occurred, dumping registers now: ", 0xd, 0xa, 0 kernel_found: db "Found kernel at cluster ", 0 kernel_loading: db 0xd, 0xa, "Loading kernel...", 0xd, 0xa, 0 kernel_loaded: db "Kernel successfully loaded.", 0xd, 0xa, "Setting up kernel environment and running kernel...", 0xd, 0xa, 0 -missing_kernel: db "Could not find KERNEL.BIN", 0xd, 0xa, 0 +missing_kernel: db "Could not find KERNEL.ELF", 0xd, 0xa, 0 eax_s: db "EAX: ", 0 ebx_s: db "EBX: ", 0 ecx_s: db "ECX: ", 0 diff --git a/boot/x86/stage3/paging.c b/boot/x86/stage3/paging.c index 0482ded..5a0e5f7 100644 --- a/boot/x86/stage3/paging.c +++ b/boot/x86/stage3/paging.c @@ -1,12 +1,9 @@ /* Code for enabling paging */ #include +#include -#define ADDRESS_NOT_ALIGNED 1 -#define INVL_ADDRESS 2 -#define ADDRESS_ALREADY_MAPPED 3 -#define ADDRESS_RANGE_MISMATCHED 4 - +/* Preallocated page tables. */ static uint32_t page_directory[1024] __attribute__((aligned(4096))) __attribute__((section(".data"))); static uint32_t page_table_firstmb[1024] __attribute__((aligned(4096))) __attribute__((section(".data"))); static uint32_t page_table_kernel[1024] __attribute__((aligned(4096))) __attribute__((section(".data"))); diff --git a/boot/x86/stage3/paging.h b/boot/x86/stage3/paging.h new file mode 100644 index 0000000..487943e --- /dev/null +++ b/boot/x86/stage3/paging.h @@ -0,0 +1,13 @@ +#ifndef BOOT_X86_PAGING_H +#define BOOT_X86_PAGING_H + +#define ADDRESS_NOT_ALIGNED 1 +#define INVL_ADDRESS 2 +#define ADDRESS_ALREADY_MAPPED 3 +#define ADDRESS_RANGE_MISMATCHED 4 + +extern int map_range(void *phys_start, void *phys_end, void *virt_start, void *virt_end, int flags); +extern void set_up_page_directory(); +extern void enable_paging(); + +#endif diff --git a/boot/x86/stage3/prekernel.c b/boot/x86/stage3/prekernel.c new file mode 100644 index 0000000..280c350 --- /dev/null +++ b/boot/x86/stage3/prekernel.c @@ -0,0 +1,62 @@ +#include +#include + +/* This bit of code will be run right after the segment registers have been set + * up for protected mode. */ + +const char *error_messages[] = { + "Tried to page an invalid address, the bootloader is buggy!", + "Tried to page an invalid address, the bootloader is buggy!", + "Tried to page an invalid address, the bootloader is buggy!", + "Tried to page an invalid address, the bootloader is buggy!", + "KERNEL.ELF is not a valid ELF file!", + "KERNEL.ELF is a non-x86 or userspace executable!", + "KERNEL.ELF is not an executable ELF file!" +}; + +void printerr(const char *error) +{ + char *message = (char *) error; + for (int i=0;;i++) { + char temp = *message; + if (!temp) return; + *(char *) (0xb8000+i*2) = temp; + *(char *) (0xb8000+1+i*2) = 0xcf; + message++; + } +} + +void halt() +{ +loop: + asm("hlt":); + goto loop; +} + +void run_kernel(void *e820_map, unsigned int e820_map_size, struct elf_header *kernel, unsigned int kernel_size) +{ + /* Before trying to parse our kernel ELF, let's set up paging. */ + unsigned int bootloader_mem_size = 0x100000 + kernel_size; + + /* Align the size to a 4K boundary. */ + if (bootloader_mem_size & 0xfff) { + bootloader_mem_size += 0x1000; + bootloader_mem_size &= ~0xfff; + } + + /* Map the bootloader memory. */ + int ret = map_range(0, (void *) bootloader_mem_size, 0, (void *) bootloader_mem_size, 2); + if (ret) { + printerr(error_messages[ret-1]); + halt(); + } + set_up_page_directory(); + enable_paging(); + + /* Parse and run the kernel ELF. */ + ret = execute_elf(kernel, e820_map, e820_map_size); + if (ret) { + printerr(error_messages[ret-1]); + halt(); + } +} diff --git a/kernel/entry.s b/kernel/entry.s index c38ac76..d6490a1 100644 --- a/kernel/entry.s +++ b/kernel/entry.s @@ -2,12 +2,31 @@ bits 32 extern kmain extern __STACK_BOTTOM__ +section .text global _start _start: + ; Here, the stack will look like: + ; return address, map pointer, map size. + + ; Skip the return address. + add esp, 4 + ; Save the kernel arguments. + ; Can this be done without the global variables? + pop dword [e820_map] + pop dword [e820_map_size] + sub esp, 12 + ; Do the stack switch. mov ebp, __STACK_BOTTOM__ mov esp, ebp - push ebx - push edi + ; Restore the kernel arguments. + push dword [e820_map_size] + push dword [e820_map] + ; Call the actual kernel. call kmain hlt jmp $-1 + +; Temporarily save arguments here to survive the upcoming stack switch. +section .bss +e820_map: resd 1 +e820_map_size: resd 1 diff --git a/kernel/linker.ld b/kernel/linker.ld index a730075..a6fb8e4 100644 --- a/kernel/linker.ld +++ b/kernel/linker.ld @@ -1,5 +1,4 @@ ENTRY(_start) -OUTPUT_FORMAT(binary) SECTIONS { diff --git a/nameless2disk b/nameless2disk index 28b3427..ddd8960 100755 --- a/nameless2disk +++ b/nameless2disk @@ -1,7 +1,7 @@ #!/bin/sh # Shell script to install Nameless to a disk. -BINARIES=( boot/x86/mbr boot/x86/vbr-fat32 boot/x86/stage3/LOADER.BIN kernel/kernel.bin ) +BINARIES=( boot/x86/mbr boot/x86/vbr-fat32 boot/x86/stage3/LOADER.BIN kernel/kernel.elf ) check_binaries() { for i in "${BINARIES[@]}"; do @@ -72,7 +72,7 @@ install_blkdev() { exit 1 fi cp boot/x86/stage3/LOADER.BIN $mountpoint/LOADER.BIN - cp kernel/kernel.bin $mountpoint/KERNEL.BIN + cp kernel/kernel.elf $mountpoint/KERNEL.ELF if ! [ $? -eq 0 ]; then echo An error occurred! exit 1 -- 2.39.2