08a1a9033a
boot/bios/ now holds the MBR, the El Torito stub and the real-mode stage 2; boot/uefi/ is empty and documented. Separate directories rather than #ifdefs, because the two share almost nothing. A BIOS loader lives in 16-bit real mode, reaches the firmware through software interrupts, and walks itself up into long mode. A UEFI loader is a 64-bit PE that the firmware has already placed in long mode with paging on, calling services through a table of function pointers. What they do share is the hand-off contract, which boot/README.md now writes down: ELF segments placed, long mode, a 24-byte-entry memory map at E820_MAP_ADDR, framebuffer geometry at VBE_INFO_ADDR. That contract is the point of documenting it now. UEFI's GetMemoryMap returns EFI_MEMORY_DESCRIPTORs, and the right move is to translate them into the entries kernel/arch/x86_64/e820.c already parses rather than teach the kernel a second format. Build output paths under $(BUILD)/boot are unchanged; only sources moved.
91 lines
3.7 KiB
Shell
91 lines
3.7 KiB
Shell
#!/bin/sh
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# Build a bootable SchOS ISO.
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#
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# tools/posix/mkiso.sh [output.iso]
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#
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# The disc boots through El Torito's "no emulation" mode, which is the only
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# one of the three that fits how SchOS actually loads itself.
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#
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# floppy emulation caps the image at 2.88 MB; the ramdisk-root kernel
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# alone is bigger than that.
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# hard disk emulation presents the image through the BIOS's INT 13h, and
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# SchOS's loader does not use INT 13h -- it drives
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# the IDE controller's registers directly, which
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# cannot reach a BIOS-emulated drive.
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# no emulation the BIOS loads a chosen run of sectors at 0x7C00
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# and gets out of the way. That is this.
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#
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# So the layout below is deliberate: -boot-load-size is 1 + STAGE2_SECTORS,
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# which makes the BIOS place both boot/cdboot and the whole of stage2 in memory
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# before anything of ours runs. That puts stage2 at 0x7E00 -- byte for byte the
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# arrangement bootasm.S produces on a hard disk. From there the only difference
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# is that stage2main.c reads the kernel back with ATAPI instead of ATA.
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#
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# STAGE2_SECTORS comes from the environment, set by the Makefile, because this
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# same number also lives in boot/bios/bootasm.S, boot/bios/stage2main.c and the dd offsets
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# in schos.img's recipe. It was previously written out by hand in three
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# separate spots in this file alone, and raising it for the boot logo is what
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# turned that from a latent hazard into a broken image.
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#
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# NOT using -boot-info-table on purpose: it patches 56 bytes over offset 8 of
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# the boot image, which is the middle of cdboot's code. stage2main.c finds
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# where it was loaded from by reading the El Torito boot catalog instead.
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set -e
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BUILD=${BUILD:-build}
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OUT=${1:-schos.iso}
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STAGE2_SECTORS=${STAGE2_SECTORS:-48}
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STAGE2_BYTES=$((STAGE2_SECTORS * 512))
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LOAD_SIZE=$((1 + STAGE2_SECTORS))
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STAGING="$BUILD/iso"
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CDBOOT="$BUILD/boot/cdboot"
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STAGE2="$BUILD/boot/stage2"
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KERNEL="$BUILD/kernel/kernel"
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for f in "$CDBOOT" "$STAGE2" "$KERNEL"; do
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[ -f "$f" ] || { echo "mkiso: missing $f -- run make first" >&2; exit 1; }
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done
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# The three pieces must be contiguous and at these exact sizes: stage2main.c's
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# readseg() finds the kernel at sector (1 + STAGE2_SECTORS) of the boot image,
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# so a short stage2 would silently shift the kernel out from under it.
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cdboot_sz=$(wc -c < "$CDBOOT")
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stage2_sz=$(wc -c < "$STAGE2")
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[ "$cdboot_sz" -eq 512 ] || { echo "mkiso: cdboot is $cdboot_sz bytes, expected 512" >&2; exit 1; }
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[ "$stage2_sz" -eq "$STAGE2_BYTES" ] || { echo "mkiso: stage2 is $stage2_sz bytes, expected $STAGE2_BYTES (STAGE2_SECTORS=$STAGE2_SECTORS)" >&2; exit 1; }
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rm -rf "$STAGING"
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mkdir -p "$STAGING/boot"
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cat "$CDBOOT" "$STAGE2" "$KERNEL" > "$STAGING/boot/schos.bin"
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# xorriso if it is here, mkisofs otherwise. Both accept the El Torito flags
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# below unchanged -- xorriso's -as mkisofs mode exists precisely to be
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# argument-compatible with it. The fallback is not academic: there is no xorriso
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# package for Windows in scoop, where this is developed, but cdrtools provides
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# mkisofs.exe.
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if command -v xorriso >/dev/null 2>&1; then
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MKISOFS="xorriso -as mkisofs"
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elif command -v mkisofs >/dev/null 2>&1; then
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MKISOFS="mkisofs"
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else
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echo "mkiso: need xorriso or mkisofs on PATH" >&2
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echo " Windows: scoop install cdrtools" >&2
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echo " Debian/Ubuntu: apt install xorriso" >&2
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exit 1
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fi
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$MKISOFS \
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-quiet \
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-V SCHOS \
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-A "SchOS" \
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-b boot/schos.bin \
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-no-emul-boot \
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-boot-load-size "$LOAD_SIZE" \
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-o "$OUT" \
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"$STAGING"
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echo "==> $OUT ($(wc -c < "$OUT") bytes)"
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echo " qemu-system-x86_64 -cdrom $OUT -boot d"
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