commit 85af2114c6d7be7608c93503c8a6f3521f5e981f
parent 1e431b3fe0bd829d8b5dbe65cbae17c93753aa2f
Author: Georges Dupéron <georges.duperon@gmail.com>
Date: Sat, 28 Jul 2018 02:22:07 +0200
ms-dos: CR+LF line endings, avoid lines longer than 8192, add [pause|exit] argument to .bat and sh code
Diffstat:
2 files changed, 49 insertions(+), 10 deletions(-)
diff --git a/Makefile b/Makefile
@@ -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 $@
diff --git a/example-os/os.asm b/example-os/os.asm
@@ -3,7 +3,17 @@
db "#!/usr/bin/env sh", 0x0a
db ": <<'EOF'", 0x0a
-db "GOTO msdos", 0x0a
+;;; Starting from here until EOF, all data is effectively ignored by Unix shells
+;;; End of line for MS-DOS, so that it correctly processes the comment
+db 0x0d, 0x0a
+
+;;; The GOTO target must not be more than one block away (512 bytes by default
+;;; on some systems) apparently, so it is impractical since the target is
+;;; so far away in our case. Instead, we use a comment, but if there are some
+;;; compatibility issues with the comment syntax, we could likely still use
+;;; GOTO and insert intermediate jump points.
+;; db "GOTO msdos", 0x0d, 0x0a
+db ":: "
;;; The #!… above is interpreted as … jnz short 0x7c78 in x86 assembly.
times 0x7c78-0x7c00-($-$$) db 0
@@ -66,24 +76,44 @@ db 0x55, 0xaa ;; 0x1fe End the bootsector with 55 AA, which is the MBR signatur
;;; Leave some space for the GPT header and partition table entries (LBA0 = MBR, LBA1 = header, LBA2..33 = GPT partition tables)
times (34*512)-($-$$) 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
