Fix Linux kernel handoff: GDT selectors, E820 map, jump_linux

Makefile

@@ -2,21 +2,26 @@ GAS       = as
 GAS_FLAGS = --32
 
 LD        = ld
-LD_FLAGS  = --oformat binary -m elf_i386 -s -nostdlib
+LD_FLAGS  = -m i386pe -s -nostdlib --image-base 0
+
+OBJCOPY   = objcopy
 
 CC        = gcc
 CC_FLAGS  = -m32 -march=i386 -fno-pic -static -fno-asynchronous-unwind-tables \
             -fno-stack-protector -ffreestanding -nostdlib -O2
 
-DD        = dd
+PS        = powershell -NoProfile -Command
+QEMU      ?= C:/Program Files/qemu/qemu-system-i386.exe
 
+STAGE2_SECTORS = 127
+IMAGE_SIZE_MB = 64
 
 BUILD_DIR = ./build
 SRC_DIR = ./src
 
 
 # not files
-.PHONY: all clean run
+.PHONY: all clean run install check-stage2-size
 
 
 # default option: make .img file
@@ -25,22 +30,22 @@ all: $(BUILD_DIR)/bootloader.img
 
 # get .img from stages
 $(BUILD_DIR)/bootloader.img: $(BUILD_DIR)/fstage.bin $(BUILD_DIR)/sstage.bin
-	# create disk img
-	$(DD) if=/dev/zero of=$@ bs=1M count=64
-	# write Stage 1
-	$(DD) if=$(BUILD_DIR)/fstage.bin of=$@ bs=1 count=446 conv=notrunc
-	# write Stage 2 + 2.5
-	$(DD) if=$(BUILD_DIR)/sstage.bin of=$@ bs=512 seek=1 conv=notrunc
+	$(PS) "$$fs=[IO.File]::Open('$@',[IO.FileMode]::Create,[IO.FileAccess]::ReadWrite); $$fs.SetLength($(IMAGE_SIZE_MB)MB); $$fs.Close()"
+	$(PS) "$$b=[IO.File]::ReadAllBytes('$(BUILD_DIR)/fstage.bin'); $$fs=[IO.File]::Open('$@',[IO.FileMode]::Open,[IO.FileAccess]::ReadWrite); $$fs.Write($$b,0,446); $$fs.Seek(510,[IO.SeekOrigin]::Begin) > $$null; $$fs.Write($$b,510,2); $$fs.Close()"
+	$(PS) "$$b=[IO.File]::ReadAllBytes('$(BUILD_DIR)/sstage.bin'); $$fs=[IO.File]::Open('$@',[IO.FileMode]::Open,[IO.FileAccess]::ReadWrite); $$fs.Seek(512,[IO.SeekOrigin]::Begin) > $$null; $$fs.Write($$b,0,$$b.Length); $$fs.Close()"
 
 
 # link asm code to .bin
 $(BUILD_DIR)/fstage.bin: $(BUILD_DIR)/fstage.o
-	$(LD) $(LD_FLAGS) -Ttext 0x7c00 -o $@ $<
+	$(LD) $(LD_FLAGS) -Ttext 0x7c00 -e _start -o $(BUILD_DIR)/fstage.pe $<
+	$(OBJCOPY) -O binary -j .text $(BUILD_DIR)/fstage.pe $@
 
 
 # link stage 2 asm and C code to .bin
 $(BUILD_DIR)/sstage.bin: $(BUILD_DIR)/sstage.o $(BUILD_DIR)/sstagec.o
-	$(LD) $(LD_FLAGS) -Ttext 0x8000 -o $@ $^
+	$(LD) $(LD_FLAGS) -Ttext 0x7e00 -e stage2_start -o $(BUILD_DIR)/sstage.pe $^
+	$(OBJCOPY) -O binary $(BUILD_DIR)/sstage.pe $@
+	powershell -NoProfile -Command "if ((Get-Item '$@').Length -gt ($(STAGE2_SECTORS) * 512)) { throw 'Stage 2 is larger than $(STAGE2_SECTORS) sectors' }"
 
 
 # compile C code to .o
@@ -55,14 +60,22 @@ $(BUILD_DIR)/%.o: $(SRC_DIR)/*/%.asm | $(BUILD_DIR)
 
 # create ./build folder if not found
 $(BUILD_DIR):
-	mkdir -p $(BUILD_DIR)
+	if not exist "$(BUILD_DIR)" mkdir "$(BUILD_DIR)"
+
+
+# install loader into an existing raw disk image with an ext2 Linux partition.
+# Usage: make install DISK=debian-ext2.img
+install: $(BUILD_DIR)/fstage.bin $(BUILD_DIR)/sstage.bin
+	@if "$(DISK)" == "" (echo DISK is not set. Usage: make install DISK=debian-ext2.img & exit /b 1)
+	$(PS) "$$b=[IO.File]::ReadAllBytes('$(BUILD_DIR)/fstage.bin'); $$fs=[IO.File]::Open('$(DISK)',[IO.FileMode]::Open,[IO.FileAccess]::ReadWrite); $$fs.Write($$b,0,446); $$fs.Seek(510,[IO.SeekOrigin]::Begin) > $$null; $$fs.Write($$b,510,2); $$fs.Close()"
+	$(PS) "$$b=[IO.File]::ReadAllBytes('$(BUILD_DIR)/sstage.bin'); $$fs=[IO.File]::Open('$(DISK)',[IO.FileMode]::Open,[IO.FileAccess]::ReadWrite); $$fs.Seek(512,[IO.SeekOrigin]::Begin) > $$null; $$fs.Write($$b,0,$$b.Length); $$fs.Close()"
 
 
 # run bootloader.img via qemu
 run: $(BUILD_DIR)/bootloader.img
-	qemu-system-i386 -drive format=raw,file=$<
+	"$(QEMU)" -m 256M -drive format=raw,file=$< -serial stdio
 
 
 # cleanup build artifacts
 clean:
-	rm -rf $(BUILD_DIR)
+	if exist "$(BUILD_DIR)" rmdir /s /q "$(BUILD_DIR)"

README.md

@@ -1,5 +1,47 @@
 # PSLBoot
 Polytech Simple Linux Bootloader **(WIP)**
 ___
-# Notes
-- **TODO**: Update Makefile when sources are complete.
+# What works
+
+PSLBoot can load a Linux bzImage and initrd from the first Linux/ext2
+partition of a raw QEMU IDE disk. Stage 2 is stored in the post-MBR gap
+starting at LBA 1, so create the first partition at the usual 1 MiB offset
+or later.
+
+# Build
+
+```sh
+make
+```
+
+This creates `build/bootloader.img`, mostly useful as a build artifact sanity
+check. For a real Debian disk image, install the loader into an existing raw
+image:
+
+```sh
+make install DISK=debian-ext2.img
+```
+
+The install target preserves the partition table, writes MBR boot code, writes
+the boot signature, and writes Stage 2 at LBA 1.
+
+# Debian/ext2 disk expectations
+
+- QEMU disk must be attached as the primary IDE disk.
+- The first Linux partition must contain an ext2 filesystem, not ext4-with-extents.
+- Kernel/initrd are searched as `/boot/vmlinuz`, `/boot/initrd.img`, then by
+  `vmlinuz*` and `initrd.img*` inside `/boot`.
+- Kernel command line is currently built in as:
+  `root=/dev/sda1 ro console=tty0 console=ttyS0,115200n8`.
+
+Example run after installing into a prepared disk:
+
+```sh
+make run
+```
+
+or directly:
+
+```sh
+"C:/Program Files/qemu/qemu-system-i386.exe" -m 256M -drive format=raw,file=debian-ext2.img -serial stdio
+```

src/stage-1/fstage.asm

@@ -1,82 +1,129 @@
-################################################################################
-#
-#   fstage.asm
-#
-#   OS CW26-1. Polytech Simple Linux Bootloader. Stage 1.
-#
-#
-#   Recommended build command:
-#       $ as --32 -o fstage.o fstage.asm
-#       $ ld -Ttext 0x7c00 --oformat binary -m elf_i386 -o fstage.bin fstage.o
-#
-################################################################################
-
-
-.code16
-.att_syntax
-
-.section .text
-.globl _start
-
-
-_start:
-    # ==== init
-    cli
-    xor %ax, %ax
-    mov %ax, %ds
-    mov %ax, %es
-    mov %ax, %ss
-    mov $0x7C00, %sp
-    sti
-
-    mov %dl, boot_drive # saving boot drive number
-
-    # ==== check extensions present
-    mov $0x41, %ah
-    mov boot_drive, %dl
-    mov $0x55AA, %bx
-    int $0x13
-    jc disk_error
-
-    # ==== loading Stage 2 from boot drive
-    lea dap, %si
-    mov $0x42, %ah
-    mov boot_drive, %dl
-    int $0x13
-    jc disk_error
-
-    ljmp $0x0000, $0x7E00 # passing control to Stage 2
-
-
-disk_error:
-    mov $err_msg, %si
-.loop:
-    lodsb
-    or %al, %al
-    jz hang
-    xor %bh, %bh
-    mov $0x0E, %ah
-    int $0x10
-    jmp .loop
-hang:
-    hlt
-    jmp hang
-
-
-dap: # Disk Address Packet for int 0x13 (ah = 0x42)
-    .byte 0x10     # struct size
-    .byte 0x00     # reserved
-    .word 16       # sector amt
-    .word 0x7E00   # offset
-    .word 0x0000   # segment
-    .quad 1        # LBA-address
-
-boot_drive: .byte 0
-err_msg: .asciz "Disk error!"
-
-
-.zero (446 - (. - _start)) # padding before partition table
-
-.zero 64    # partition table (manual filling)
-
-.word 0xAA55    # bootsect signature
+################################################################################
+#
+#   fstage.asm
+#
+#   OS CW26-1. Polytech Simple Linux Bootloader. Stage 1.
+#
+#
+#   Recommended build command:
+#       $ as --32 -o fstage.o fstage.asm
+#       $ ld -Ttext 0x7c00 --oformat binary -m elf_i386 -o fstage.bin fstage.o
+#
+################################################################################
+
+
+.code16
+.att_syntax
+
+.section .text
+.globl _start
+
+# Where we stash the BIOS E820 memory map for Stage 2:
+#   0x4000        : dword, number of entries
+#   0x4004 + n*20 : entries (each: u64 addr, u64 size, u32 type)
+E820_COUNT = 0x4000
+E820_ENTRIES = 0x4004
+
+
+_start:
+    # ==== init
+    cli
+    xor %ax, %ax
+    mov %ax, %ds
+    mov %ax, %es
+    mov %ax, %ss
+    mov $0x7C00, %sp
+    sti
+
+    mov %dl, boot_drive # saving boot drive number
+
+    # ==== collect BIOS E820 memory map (int 0x15, eax=0xE820)
+    call do_e820
+
+    # ==== check extensions present
+    mov $0x41, %ah
+    mov boot_drive, %dl
+    mov $0x55AA, %bx
+    int $0x13
+    jc disk_error
+
+    # ==== loading Stage 2 from boot drive
+    lea dap, %si
+    mov $0x42, %ah
+    mov boot_drive, %dl
+    int $0x13
+    jc disk_error
+
+    ljmp $0x0000, $0x7E00 # passing control to Stage 2
+
+
+# ==== Build the E820 map at E820_ENTRIES, count at E820_COUNT.
+do_e820:
+    push %es
+    pusha
+    xor %ax, %ax
+    mov %ax, %es
+    mov $E820_ENTRIES, %di   # es:di -> destination buffer
+    xor %ebx, %ebx           # continuation = 0
+    xor %bp, %bp             # entry counter
+    mov $0x534D4150, %edx    # 'SMAP'
+    mov $0xE820, %eax
+    mov $24, %ecx
+    int $0x15
+    jc .e820_done            # carry on first call => unsupported
+    cmp $0x534D4150, %eax    # BIOS must return 'SMAP' in eax
+    jne .e820_done
+    jmp .e820_check
+.e820_loop:
+    mov $0xE820, %eax
+    mov $24, %ecx
+    int $0x15
+    jc .e820_done            # carry => end of list
+.e820_check:
+    jcxz .e820_skip          # length-0 entry => skip
+    inc %bp
+    add $20, %di             # advance to next 20-byte slot
+.e820_skip:
+    test %ebx, %ebx          # ebx == 0 => that was the last entry
+    jz .e820_done
+    jmp .e820_loop
+.e820_done:
+    movzwl %bp, %eax
+    mov %eax, (E820_COUNT)
+    popa
+    pop %es
+    ret
+
+
+disk_error:
+    mov $err_msg, %si
+.loop:
+    lodsb
+    or %al, %al
+    jz hang
+    xor %bh, %bh
+    mov $0x0E, %ah
+    int $0x10
+    jmp .loop
+hang:
+    hlt
+    jmp hang
+
+
+dap: # Disk Address Packet for int 0x13 (ah = 0x42)
+    .byte 0x10     # struct size
+    .byte 0x00     # reserved
+    .word 127      # sector amt
+    .word 0x7E00   # offset
+    .word 0x0000   # segment
+    .quad 1        # LBA-address
+
+boot_drive: .byte 0
+err_msg: .asciz "Disk error!"
+
+
+.zero (446 - (. - _start)) # padding before partition table
+
+.zero 64    # partition table (manual filling)
+
+.word 0xAA55    # bootsect signature