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ms-dos: CR+LF line endings, avoid lines longer than 8192, add [pause|exit] argument to .bat and sh code

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This commit is contained in:
Georges Dupéron 2018-07-28 02:22:07 +02:00
parent 1e431b3fe0
commit 85af2114c6
2 changed files with 49 additions and 10 deletions
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9
Makefile
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@ -258,6 +258,7 @@ ${os_filename}: build/os.32k build/os.iso build/os.fat12 build/os.zip.adjusted \
${dep_bytes_header_32k_size} \
${dep_bytes_fat12_start} \
${dep_bytes_fat12_size} \
${dep_bytes_gpt_mirror_start} \
${dep_bytes_gpt_mirror_end} \
${dep_sectors_fat12_start} \
${dep_sectors_fat12_size} \
@ -287,6 +288,14 @@ ${os_filename}: build/os.32k build/os.iso build/os.fat12 build/os.zip.adjusted \
printf "1\nN\n"; \
printf "01\nY\nN\n"; \
printf "p\no\nw\nY\n") | while read str; do echo "$$str"; printf "\033[1;33m%s\033[m\n" "$$str" >&2; sleep 0.01; done | gdisk $@
# Inject MS-DOS newlines (CR+LF) and comments (":: ") in the GUID field of unused partition table entries,
# so that the part that is to be skipped by MS-DOS does not form a line longer than the MS-DOS maximum
# line length (8192 excluding CR+LF). $i below is the partition entry number, starting from 1
# The numbers 55 and 118 are arbitrarily chosen so that the space between two CR+LF is less than 8192.
for i in 55 118; do \
printf "\r\n:: %02x" $$i | dd bs=1 seek=$$(( 1024 + ( ($$i) - 1) * 128 + 16)) count=7 conv=notrunc of=$@; \
printf "\r\n:: %02x" $$i | dd bs=1 seek=$$(( ${bytes_gpt_mirror_start} + ( ($$i) - 1) * 128 + 16)) count=7 conv=notrunc of=$@; \
done
# splice in zip at the end
set -x; dd skip=${bytes_zip_start} seek=${bytes_zip_start} bs=1 conv=notrunc if=build/os.zip.adjusted of=$@
chmod a+x-w $@

50
example-os/os.asm
View File

@ -3,7 +3,17 @@
db "#!/usr/bin/env sh", 0x0a
db ": <<'EOF'", 0x0a
db "GOTO msdos", 0x0a
;;; Starting from here until EOF, all data is effectively ignored by Unix shells
;;; End of line for MS-DOS, so that it correctly processes the comment
db 0x0d, 0x0a
;;; The GOTO target must not be more than one block away (512 bytes by default
;;; on some systems) apparently, so it is impractical since the target is
;;; so far away in our case. Instead, we use a comment, but if there are some
;;; compatibility issues with the comment syntax, we could likely still use
;;; GOTO and insert intermediate jump points.
;; db "GOTO msdos", 0x0d, 0x0a
db ":: "
;;; The #!… above is interpreted as … jnz short 0x7c78 in x86 assembly.
times 0x7c78-0x7c00-($-$$) db 0
@ -66,24 +76,44 @@ db 0x55, 0xaa ;; 0x1fe End the bootsector with 55 AA, which is the MBR signatur
;;; Leave some space for the GPT header and partition table entries (LBA0 = MBR, LBA1 = header, LBA2..33 = GPT partition tables)
times (34*512)-($-$$) db 0
;;; The MS-DOS maximum line length is 8192 (excluding the \r\n),
;;; but the GPT partition table is a bit more than 16384 bytes long.
;;; We therefore inject in the Makefile intermediate \r\n in some
;;; unused partition entries, after the disk image has been
;;; partitioned using gdisk.
;;; End of line for MS-DOS, so that it correctly processes the GOTO instruction
db 0x0d, 0x0a
db "GOTO msdos", 0x0d, 0x0a
;;; After the bootsector, close the sh here-document skipped via : <<'EOF'
db 0x0a
db "EOF", 0x0a
db "echo Hello world by the OS, from sh!", 0x0a
db "while sleep 10; do :; done", 0x0a
db "if test $# -ge 1 && test ", 0x22, "$1", 0x22, " = exit", 0x0a
db "then", 0x0a
db ":", 0x0a
db "else", 0x0a
db "while sleep 10", 0x0a, "do", 0x0a, ":", 0x0a, "done", 0x0a
db "fi", 0x0a
db "exit", 0x0a
;;; for good measure: go into an infinite loop if the exit did not happen.
db "while :; do sleep 1; done", 0x0a
;;; end of the SH section, everything until this point is skipped by MS-DOS batch due to the GOTO'
db ":msdos", 0x0a
db "@cls", 0x0a
db "@echo Hello world by the OS, from MS-DOS!", 0x0a
db "command.com", 0x0a
db "exit", 0x0a
;;; end of the SH section, everything until this point is skipped by MS-DOS batch due to the GOTO
;;; End of line for MS-DOS, so that it correctly processes the :msdos label
db 0x0d, 0x0a
db ":msdos", 0x0d, 0x0a
db "@cls", 0x0d, 0x0a
db "echo Hello world by the OS, from MS-DOS!", 0x0d, 0x0a
db "@goto %1 :pause", 0x0d, 0x0a
db ":pause", 0x0d, 0x0a
db "@pause", 0x0d, 0x0a
db ":exit", 0x0d, 0x0a
db "@exit 0", 0x0d, 0x0a
;;; for good measure: go into an infinite loop if the exit did not happen.
db ":loop", 0x0a
db "GOTO loop", 0x0a
db ":loop", 0x0d, 0x0a
db "@GOTO loop", 0x0d, 0x0a
;;; Fill up to 32k with 0. This constitutes the reserved first 32k at the beginning of an ISO9660 image.
times (32*1024)-($-$$) db 0