lDebug wants to access the environment while executing
as a device driver. Instead of building it in a variable
then copying it to 68h:0 after FDCONFIG.SYS processing,
just build it there to begin with.
To be able to return free space on larger non local disks, the redirector
needs an extension. Dosemu2 has implemented this function and FDPP
has an almost identical patch to this. If the extension is not
implemented by your chosen redirector, then fallback to the standard
110c function is done for int21/7303.
With this patch up to 2TB (with Dosemu2 reporting in 512 blocks) can be
displayed.
Also checks that the total amount of clusters is possible
for the detected file system, erroring out otherwise.
Small FAT32 is displayed in the verbose output specifically.
This should be Enhanced DR-DOS compatible.
oemboot.asm contains an optimisation to save 2 bytes,
by using mov instead of a lea with bp evaluating to
a constant value. This was needed to fit the addition
for 256 spc support. It is otherwise unrelated.
The LBA detection patch offsets in SYS have also been
updated to match the changed boot.asm offsets.
This should be compatible to Enhanced DR-DOS.
Tested by building a boot image like the following:
nasm ../ldosmbr/oldmbr.asm -o oldmbr.bin
nasm ../ldosboot/boot.asm -D_FAT16=1 -I ../lmacros/ \
-D_LOAD_NAME="'LDEBUG'" -o boot16.bin
nasm bootimg.asm -I ../lmacros/ -o disk16.img \
-D_MBR -D_ALIGNDATA -D_BOOTPATCHFILE=boot16.bin \
-D_MBRPATCHFILE=oldmbr.bin -D_BPE=16 \
-D_SPI='(_SPC * 5000)' -D_NUMROOT=512 -D_SPC=256 \
-D_SPF='((_SPI / _SPC + 255) / 256)' \
-D_PAYLOADFILE=../ldebug/bin/ldebug.com,quit.com,\
::rename,../k256spc/bin/kernel.sys,kernel.sys,\
command.com,::fill,1,32,autoexec.bat
The repos bootimg, ldosboot, ldosmbr, and lmacros are
available at https://hg.pushbx.org/ecm/
The file ldebug.com is a recent bootable lDebug debugger.
The file command.com is a recent FreeCOM. The file quit.com
is assembled with NASM from
https://hg.pushbx.org/ecm/ldebug/file/e6035c05670a/misc/quit.asm
Run like this:
qemu-system-i386 -hda disk16.img -boot order=c -display curses
To the lDebug prompt "-" enter "boot protocol freedos",
then a "q" command. On success, the quit.com command
can be run to quit the qemu VM.
Not yet done:
- initdisk.c:512 uses MAXCLUSTSIZE defined to 128. This is
not difficult to change but it is unclear whether this
should be changed.
- The boot loaders are not yet adjuscted, requiring use of
the ldosboot or lDebug loaders instead.
- A patch for FORMAT (copylefted) version 0.91u is available
from the Enhanced DR-DOS project. Mirrored in the directory at
https://pushbx.org/ecm/download/edrdos/freedos/
This should be easy enough to update to the most recent version.
The int86 function is used to call interrupt 21h
service 32h in the reset_drive function. This
function returns a pointer using the ds register.
ds will usually point into the DOS data segment
then (for our kernel). However, the compiler
assumed ds to be unchanged.
cast array using pointer to first element [newboot] instead of pointer to whole array [&newboot] to avoid OW error W115 "&array may not produce intended result" since the address of operator "&" is not required for getting the address of an array.
The code still allows for up to 192 bytes, should that
be useful. Simply by re-assembling upxentry.asm then
re-running exeflat, the changes will be picked up.
This format has several advantages:
* The CONFIG block need not be moved.
* The entire compressed image (depacker and payload) need
not be moved another time before the UPX depacker's own
operation.
* The CONFIG block always lives at 00602h, and the kernel
need not be aware whether it was compressed for detecting
which CONFIG block to use.
* Support for compressed images beyond 64 KiB for free.
(The assembly define TEST_FILL_INIT_TEXT can be passed in
NASMENV to test this support with 32 KiB of LFSR output.)
* A subsequent commit will shorten the stub to 64 bytes,
compared to the prior 32 + 45 = 77 bytes, with no loss
of features. (The packed payload is a bit shorter too.)
* The new stub also sets ds and es to the segment value
that would point to the DOS/EXE process's PSP. This is
apparently not used by the UPX depacker but could be in
a future or past version, or if another packer is used.
