etc. The only bit of debugging left is performing dual output to both
the screen and COM1. Also, the twiddle is still disabled since it seems
to do weird things to the serial dump. cdboot now has 880 bytes to spare.
to the El Torito standard for CD booting, a CD may boot in "No emulation"
mode without using a floppy image. In this mode, the BIOS loads a program
off of the CD into memory and creates a BIOS device using 2048 byte sectors
for the CD. According to the standard, this program can be up to 0xFFFF
virtual (512-byte) sectors long. The old cdldr depended on this by having
the BIOS load the entire loader and the small cdldr stub as one binary
similar to pxeboot so that cdldr didn't have to read the CD to find the
loader. However, the NT no emulation loader just uses 1 disk sector
(4 virtual sectors), so it seems that at least some BIOS writers just did
enough to get NT to boot by only loading 1 sector and ignoring the sector
count. Thus, while cdldr should have worked in theory, it doesn't in
practice. This replacment fits entirely in 1 sector and includes simple
ISO 9660 support. It looks for /boot/loader on the CD and loads it up
using the BIOS. This allows us to not have to depend on the limited size
of floppy images but use a full GENERIC kernel for CD-ROM installs in the
future, among other things.
This version of cdboot is a bit bloated as it includes some useful
debugging routines that people can pull to use in other x86 assembly
modules. Even with all the debugging cruft, we still have 272 bytes to
spare.
when debugging boot problems. It is not on by default but is enabled via
the BTX_SERIAL variable. The port and speed can be set via the same
variables used by boot2 and the loader.
dedicated" mode. This was specifying that there are 256 (illegal!)
heads on the disk. If bioses store that in a byte, and it gets truncated
to 0, then that almost certainly causes the infamous divide-by-zero
nightmare.
This is also most likely the reason why the Thinkpad T20/A20 series
were locking up when FreeBSD was installed. This is also the most likely
reason why a boot1 being present causes an IA64 box to lock up at boot.
(removing the "part4" stuff from boot1.s fixes the IA64 boxes and would
most likely have fixed the T20/A20 and some TP600E series thinkpads)
- When the video BIOS is called to clear the region (x, y)-(79, 24)
(by scrolling), the slashed region in Fig.1 is cleared. CD() is
supposed to clear the region shown in Fig.2.
x x
+-------+ +-------+
| | | |
y| ////| y| ////|
| ////| |///////|
| ////| |///////|
+-------+ +-------+
Fig.1 Fig.2
- Don't move the cursor during this operation.
- Be consistent about placing spaces around keywords and
operators; don't mix statements like "if(A==B)" and "if (X == Y)",
"return(0)" and "return (-1)", "P=10" and "Q = 0", etc.
- Consitently indent lines. It's not good to indent by 8 columns
in one part of the file, and by 4 columns in the other part.
is turned off by default and could be enabled by defining LOADER_BZIP2_SUPPORT
make variable. Also make gzip support optional (turned on by default) -
it could be turned off via LOADER_NO_GZIP_SUPPORT make variable.
Please note, that due to limit on the amount of memory available to the
loader(8), it is possible to load modules/kernels compressed with the smallest
block size supported by the bzip2 - 100k (`-1' bzip2(1) option), however
even in this mode bzip2(1) usually provides better compression ratio than
gzip(1) in its best compression mode.
MFC after: 1 month
the ACPI module if the system apperars to be ACPI compliant.
This is an initial cut; the load should really be done by Forth support
code, and we should check both the BIOS build date and a blacklist.
actual end of the section. The new gas (binutils) puts in additional padding
which was misaligning the concatenated btx loader.
Reported by: Oliver Hartmann <ohartman@klima.physik.uni-mainz.de>,
Harti Brandt <brandt@fokus.gmd.de>
Tested by: Oliver Hartmann <ohartman@klima.physik.uni-mainz.de>,
David Wolfskill <dhw@whistle.com>, ps
Reviewed by: jhb
MFC after: 1 day
the first sector of the emulated floppy to contain a valid MS-DOS BPB that
it can modify. Since boot1 is the first sector of boot.flp, this resulted
in the BIOS overwriting part of boot1: specifically the function used to
read in sectors from the disk.
Submitted by: Mark Peek <mark@whistle.com>
Submitted by: Doug Ambrisko <ambrisko@ambrisko.com>
PR: i386/26382
Obtained from: NetBSD, OpenBSD (the example BPB)
MFC after: 1 month
longer includes machine/elf.h.
* consumers of elf.h now use the minimalist elf header possible.
This change is motivated by Binutils 2.11.0 and too much clashing over
our base elf headers and the Binutils elf headers.
fatal trap. Also, reload the GDT register to point to BTX's GDT before
playing around with the segment registers to return to real mode. This is
helpful if the kernel causes a fatal exception before it has setup its own
IDT and fault handlers. For example, if one happens to break mtx_init().
Without these changes BTX would recursively page fault (if paging was not
disabled) or triple fault and reset the CPU (without the GDT reload)
instead of providing a potentially useful register dump.
Reviewed by: rnordier
Taking over the sector following the MBR causes problems on some
machines, and the actual gains are fairly small in terms of how
the space is presently used.
Since we need a number of further features (eg. handling extended
partitions) that can't be readily accommodated in the basic boot0
design anyway, rather choose to implement the additional stuff
separately and concentrate on compatibility rather than features
here.
