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This commit is contained in:
parent
cbf6c48b22
commit
5b34321456
45
Makefile
45
Makefile
@ -2,7 +2,7 @@ BUILD=./build
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# Default rule
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.PHONY: default
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default: all
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default: $(BUILD)/disk.img
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# Remove all build files
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.PHONY: clean
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@ -10,16 +10,11 @@ clean:
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rm -drf $(BUILD)
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cd tetros; cargo clean
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# Make everything
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# (but don't run qemu)
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.PHONY: all
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all: img
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#
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# MARK: boot
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# MARK: disk
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#
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# Compile tetros as library
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# Compile tetros
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LIB_SRC = ./tetros/Cargo.toml ./tetros/Cargo.lock $(shell find ./tetros/src -type f)
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$(BUILD)/tetros.lib: $(LIB_SRC)
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@mkdir -p $(BUILD)
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@ -35,7 +30,7 @@ $(BUILD)/tetros.lib: $(LIB_SRC)
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-- \
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--emit link="$(CURDIR)/$@"
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# Link tetros
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# Link tetros using custom linker script
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BIOS_LD = ./tetros/linkers/x86-unknown-none.ld
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$(BUILD)/tetros.elf: $(BUILD)/tetros.lib $(BIOS_LD)
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ld \
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@ -49,13 +44,13 @@ $(BUILD)/tetros.elf: $(BUILD)/tetros.lib $(BIOS_LD)
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objcopy --only-keep-debug "$@" "$@.sym"
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objcopy --strip-debug "$@"
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# Wrap tetros in three-stage BIOS loader
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# Wrap tetros in BIOS loader
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# Parameters:
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# - BIOS_SRC: source directory of bios assembly
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# - STAGE2_SECTOR: the index of the first sector of the stage 2 binary on the disk
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BIOS_SRC = ./bios
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STAGE2_SECTOR = 1
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$(BUILD)/bios.bin: $(wildcard $(BIOS_SRC)/*.asm) $(BUILD)/tetros.elf
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$(BUILD)/disk.img: $(wildcard $(BIOS_SRC)/*.asm) $(BUILD)/tetros.elf
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@mkdir -p "$(BUILD)"
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nasm \
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-f bin \
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@ -66,30 +61,12 @@ $(BUILD)/bios.bin: $(wildcard $(BIOS_SRC)/*.asm) $(BUILD)/tetros.elf
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-i "$(BIOS_SRC)" \
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"$(BIOS_SRC)/main.asm"
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# Extract full mbr (first 512 bytes)
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$(BUILD)/mbr.bin: $(BUILD)/bios.bin
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@mkdir -p "$(BUILD)"
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@echo ""
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dd if="$<" bs=512 count=1 of="$@"
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# Extract stage 2 (rest of file)
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$(BUILD)/stage2.bin: $(BUILD)/bios.bin
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@mkdir -p "$(BUILD)"
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@echo ""
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dd if="$<" bs=512 skip=1 of="$@"
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#
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# MARK: bundle
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# MARK: qemu
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#
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# Do not use `-enable-kvm` or `-cpu host`
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# this confuses gdb.
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#
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# Make full disk image
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.PHONY: img
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img: $(BUILD)/disk.img
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$(BUILD)/disk.img: $(BUILD)/mbr.bin $(BUILD)/stage2.bin
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@mkdir -p $(BUILD)
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@echo ""
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dd if="$(BUILD)/mbr.bin" of=$@ conv=notrunc bs=512
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dd if="$(BUILD)/stage2.bin" of=$@ conv=notrunc seek=$(STAGE2_SECTOR) bs=512
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.PHONY: qemu
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qemu: $(BUILD)/disk.img
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@ -129,5 +106,3 @@ qemu-gdb: $(BUILD)/disk.img
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-gdb tcp::26000 \
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-S
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# Do not use `-enable-kvm` or `-cpu host`,
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# this confuses gdb.
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@ -4,27 +4,22 @@ sectalign off
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; STAGE3, a path to the stage3 binary
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; STAGE2_SECTOR, the location of stage 2
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; on the disk, in 512-byte sectors.
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; On a gpt disk, this is probably 34.
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; Stage 1 is MBR code, and should fit in LBA 0
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; (512 bytes). Layout is as follows:
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; (Format is `offset, length: purpose`)
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; 0, 424: x86 boot code
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; 440, 4: Unique disk signature
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; 444, 2: unknown
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; 446, 16*4: Array of four legacy MBR records
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; 510, 2: signature 0x55 0xAA
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; 512 to end of logical block: reserved
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;
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; See https://uefi.org/specs/UEFI/2.10/05_GUID_Partition_Table_Format.html
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; BIOS loads stage 1 at 0x7C00
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ORG 0x7C00
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SECTION .text
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; stage 1 is sector 0, loaded into memory at 0x7C00
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; Stage 1 is MBR code, and should fit in LBA 0
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; (i.e, in the first 512 bytes).
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%include "stage1.asm"
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; Stage 1 is at most 440 bytes
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; This limit is set by the GPT spec.
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; See https://uefi.org/specs/UEFI/2.10/05_GUID_Partition_Table_Format.html
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;
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; This `times` will throw an error if the subtraction is negative.
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times 440-($-$$) db 0
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db 0xee
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@ -32,30 +27,39 @@ db 0xee
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times 510-($-$$) db 0
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; MBR signature.
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; This isn't loaded into memory, it's
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; only here for debugging.
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; This tells the BIOS that this disk is bootable.
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db 0x55
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db 0xaa
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; Include stage 2. This is loaded into memory by stage 1.
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;
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; Stage 2 sets up protected mode, sets up the GDT,
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; and initializes a minimal environment for stage 3.
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;
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; On a "real" boot disk, this data will not immediately follow stage 1.
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; It would be stored in a special disk partition.
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;
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; We don't need this kind of complexity here, though, so we store
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; stage 2 right after stage 1. (This is why STAGE2_SECTOR is 1.)
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;
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; This is nice, because the layout of the code on our boot disk
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; matches the layout of the code in memory. THIS IS NOT USUALLY THE CASE.
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stage2:
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%include "stage2.asm"
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align 512, db 0
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stage2.end:
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; The maximum size of stage2 is 4 KiB,
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; This fill will throw an error if the subtraction is negative.
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times (4*1024)-($-stage2) db 0
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; Pad to 0x9000.
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; This needs to match the value configured in the stage3 linker script
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; This needs to match the value configured in the Stage 3 linker script
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; TODO: why? can we make this smaller?
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times (0x9000 - 0x7c00)-($-$$) db 0
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; Include stage 3, the binary compiled from Rust sources.
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stage3:
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%defstr STAGE3_STR %[STAGE3]
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incbin STAGE3_STR
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align 512, db 0
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.end:
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; TODO: why? Of the disk, or of memory?
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; the maximum size of the boot loader portion is 384 KiB
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times (384*1024)-($-$$) db 0
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@ -1,22 +1,21 @@
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SECTION .text
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USE16
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; provide function for printing in x86 real mode
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; print a string and a newline
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; CLOBBER
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; ax
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; Print a string and a newline
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;
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; Clobbers ax
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print_line:
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mov al, 13
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call print_char
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mov al, 10
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jmp print_char
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; print a string
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; IN
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; Print a string
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;
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; Input:
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; si: points at zero-terminated String
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; CLOBBER
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; si, ax
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;
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; Clobbers si, ax
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print:
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pushf
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cld
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@ -30,8 +29,9 @@ print:
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popf
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ret
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; print a character
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; IN
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; Print a character
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;
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; Input:
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; al: character to print
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print_char:
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pusha
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@ -42,10 +42,11 @@ print_char:
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ret
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; print a number in hex
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; IN
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;
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; Input:
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; bx: the number
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; CLOBBER
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; al, cx
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;
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; Clobbers al, cx
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print_hex:
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mov cx, 4
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.lp:
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121
bios/stage1.asm
121
bios/stage1.asm
@ -1,37 +1,39 @@
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USE16
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stage1: ; dl comes with disk
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; initialize segment registers
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xor ax, ax
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stage1:
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; Initialize segment registers
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xor ax, ax ; Set ax to 0
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mov ds, ax
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mov es, ax
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mov ss, ax
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; initialize stack
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; Initialize stack pointer
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; (stack grows up)
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mov sp, 0x7C00
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; initialize CS
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; far jump sets both CS and IP to a known-good state,
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; we don't know where the BIOS put us at startup.
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; (could be 0x00:0x7C00, could be 0x7C00:0x00.
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; Not everybody follows spec.)
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push ax
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; Initialize CS
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;
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; `retf` sets both CS and IP to a known-good state.
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; This is necessary because we don't know where the BIOS put us at startup.
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; (could be 0x00:0x7C00, could be 0x7C00:0x00. Not everybody follows spec.)
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push ax ; `ax` is still 0
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push word .set_cs
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retf
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.set_cs:
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; save disk number
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; Save disk number.
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; BIOS sets `dl` to the number of
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; the disk we're booting from.
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mov [disk], dl
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; Print "Stage 1"
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mov si, stage_msg
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call print
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mov al, '1'
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call print_char
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call print_line
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; read CHS gemotry
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; read CHS gemotry, save into [chs]
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; CL (bits 0-5) = maximum sector number
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; CL (bits 6-7) = high bits of max cylinder number
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; CH = low bits of maximum cylinder number
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@ -51,11 +53,10 @@ stage1: ; dl comes with disk
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and cl, 0x3f
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mov [chs.s], cl
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; disk address of stage 2
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; (start sector)
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; First sector of stage 2
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mov eax, STAGE2_SECTOR
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; where to load stage 2
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; Where to load stage 2
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mov bx, stage2
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; length of stage2 + stage3
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@ -63,21 +64,22 @@ stage1: ; dl comes with disk
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mov cx, (stage3.end - stage2) / 512
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mov dx, 0
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; Consume eax, bx, cx, dx
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; and load code from disk.
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call load
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jmp stage2.entry
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; load some sectors from disk to a buffer in memory
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; buffer has to be below 1MiB
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; IN
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; Load sectors from disk to memory.
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; Cannot load more than 1MiB.
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;
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; Input:
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; ax: start sector
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; bx: offset of buffer
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; cx: number of sectors (512 Bytes each)
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; dx: segment of buffer
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; CLOBBER
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; ax, bx, cx, dx, si
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; TODO rewrite to (eventually) move larger parts at once
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; if that is done increase buffer_size_sectors in startup-common to that (max 0x80000 - startup_end)
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;
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; Clobbers ax, bx, cx, dx, si
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load:
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; replaced 127 with 1.
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; see https://stackoverflow.com/questions/58564895/problem-with-bios-int-13h-read-sectors-from-drive
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@ -101,44 +103,32 @@ load:
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mov [DAPACK.count], cx
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mov [DAPACK.seg], dx
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; This should be a subroutine,
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; but we don't call/ret to save a few bytes.
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; (we only use this once)
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;
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;call print_dapack
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;print_dapack:
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; Print the data we're reading
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; TODO: decode
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mov bx, [DAPACK.addr + 2]
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call print_hex
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mov bx, [DAPACK.addr]
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call print_hex
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mov al, '#'
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call print_char
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mov bx, [DAPACK.count]
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call print_hex
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mov al, ' '
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call print_char
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mov bx, [DAPACK.seg]
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call print_hex
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mov al, ':'
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call print_char
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mov bx, [DAPACK.buf]
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call print_hex
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call print_line
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;ret
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; End of print_dapack
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cmp byte [chs.s], 0
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jne .chs
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;INT 0x13 extended read does not work on CDROM!
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; Read from disk.
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;
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; Note:
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; int 0x13 extended read does not work on CDROM,
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; but we don't care. We're booting from a floppy.
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mov dl, [disk]
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mov si, DAPACK
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mov ah, 0x42
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@ -146,51 +136,6 @@ load:
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jc error ; carry flag set on error
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ret
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.chs:
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; calculate CHS
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xor edx, edx
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mov eax, [DAPACK.addr]
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div dword [chs.s] ; divide by sectors
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mov ecx, edx ; move sector remainder to ecx
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xor edx, edx
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div dword [chs.h] ; divide by heads
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; eax has cylinders, edx has heads, ecx has sectors
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; Sector cannot be greater than 63
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inc ecx ; Sector is base 1
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cmp ecx, 63
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ja error_chs
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; Head cannot be greater than 255
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cmp edx, 255
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ja error_chs
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; Cylinder cannot be greater than 1023
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cmp eax, 1023
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ja error_chs
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; Move CHS values to parameters
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mov ch, al
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shl ah, 6
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and cl, 0x3f
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or cl, ah
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shl dx, 8
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; read from disk using CHS
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mov al, [DAPACK.count]
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mov ah, 0x02 ; disk read (CHS)
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mov bx, [DAPACK.buf]
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mov dl, [disk]
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push es ; save ES
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mov es, [DAPACK.seg]
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int 0x13
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pop es ; restore EC
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jc error ; carry flag set on error
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ret
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error_chs:
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mov ah, 0
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error:
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call print_line
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