582 lines
26 KiB
Text
582 lines
26 KiB
Text
<!-- $Id: hackers.sgml,v 1.17 1999-07-28 20:26:06 nik Exp $ -->
|
|
<!-- The FreeBSD Documentation Project -->
|
|
|
|
<sect>
|
|
<heading>For serious FreeBSD hackers only<label id="hackers"></heading>
|
|
|
|
<sect1>
|
|
<heading>
|
|
What are SNAPs and RELEASEs?
|
|
</heading>
|
|
|
|
<p>There are currently three active/semi-active branches in the FreeBSD
|
|
<url url="http://www.FreeBSD.org/cgi/cvsweb.cgi" name="CVS Repository">:
|
|
|
|
<itemize>
|
|
<item><bf/RELENG_2_2/ AKA <bf/2.2-stable/ AKA <bf/"2.2 branch"/
|
|
<item><bf/RELENG_3/ AKA <bf/3.x-stable/ AKA <bf/"3.0 branch"/
|
|
<item><bf/HEAD/ AKA <bf/-current/ AKA <bf/4.0-current/
|
|
</itemize>
|
|
|
|
<p><bf/HEAD/ is not an actual branch tag, like the other two, it's
|
|
simply a symbolic constant for
|
|
<em/"the current, non-branched development stream"/ which we simply
|
|
refer to as <bf/-current/.
|
|
|
|
<p>Right now, <bf/-current/ is the 4.0 development stream and the
|
|
<bf/3.0-stable/ branch, <bf/RELENG_3/, forked off from
|
|
<bf/-current/ in Jan 1999.
|
|
|
|
<p>The <bf/2.2-stable/ branch, <bf/RELENG_2_2/, departed -current in
|
|
November 1996.
|
|
|
|
<p>The <bf/2.1-stable/ branch, <bf/RELENG_2_1_0/, departed -current in
|
|
September of 1994. This branch has been fully retired.
|
|
|
|
<sect1>
|
|
<heading>
|
|
How do I make my own custom release?<label id="custrel">
|
|
</heading>
|
|
|
|
<p>To make a release you need to do three things: First, you need to
|
|
be running a kernel with the <htmlurl
|
|
url="http://www.FreeBSD.org/cgi/man.cgi?vn" name="vn"> driver configured
|
|
in. Add this to your kernel config file and build a new kernel:
|
|
|
|
<verb>
|
|
pseudo-device vn #Vnode driver (turns a file into a device)
|
|
</verb>
|
|
|
|
<p>Second, you have to have the whole CVS repository at hand.
|
|
To get this you can use <url url="../handbook/synching.html#CVSUP" name="CVSUP">
|
|
but in your supfile set the release name to cvs and remove any tag or
|
|
date fields:
|
|
|
|
<verb>
|
|
*default prefix=/home/ncvs
|
|
*default base=/a
|
|
*default host=cvsup.FreeBSD.org
|
|
*default release=cvs
|
|
*default delete compress use-rel-suffix
|
|
|
|
## Main Source Tree
|
|
src-all
|
|
src-eBones
|
|
src-secure
|
|
|
|
# Other stuff
|
|
ports-all
|
|
www
|
|
doc-all
|
|
</verb>
|
|
|
|
<p>Then run <tt/cvsup -g supfile/ to suck all the good bits onto your
|
|
box...
|
|
|
|
<p>Finally, you need a chunk of empty space to build into. Let's
|
|
say it's in <tt>/some/big/filesystem</tt>, and from the example
|
|
above you've got the CVS repository in <tt>/home/ncvs</tt>:
|
|
|
|
<verb>
|
|
setenv CVSROOT /home/ncvs # or export CVSROOT=/home/ncvs
|
|
cd /usr/src/release
|
|
make release BUILDNAME=3.0-MY-SNAP CHROOTDIR=/some/big/filesystem/release
|
|
</verb>
|
|
|
|
<p>An entire release will be built in
|
|
<tt>/some/big/filesystem/release</tt> and you will have a full FTP-type
|
|
installation in <tt>/some/big/filesystem/release/R/ftp</tt> when you're
|
|
done. If you want to build your SNAP along some other branch than
|
|
-current, you can also add <tt/RELEASETAG=SOMETAG/ to
|
|
the make release command line above, e.g. <tt/RELEASETAG=RELENG_2_2/
|
|
would build an up-to-the- minute 2.2-STABLE snapshot.
|
|
|
|
<sect1>
|
|
<heading>How do I create customized installation disks?</heading>
|
|
|
|
<p>The entire process of creating installation disks and source and
|
|
binary archives is automated by various targets in
|
|
<tt>/usr/src/release/Makefile</tt>. The information there should
|
|
be enough to get you started. However, it should be said that this
|
|
involves doing a ``make world'' and will therefore take up a lot of
|
|
time and disk space.
|
|
|
|
<sect1>
|
|
<heading>``make world'' clobbers my existing installed binaries.</heading>
|
|
|
|
<p>Yes, this is the general idea; as its name might suggest,
|
|
``make world'' rebuilds every system binary from scratch, so you can be
|
|
certain of having a clean and consistent environment at the end (which
|
|
is why it takes so long).
|
|
|
|
<p>If the environment variable <tt/DESTDIR/ is defined while running
|
|
``<tt/make world/'' or ``<tt/make install/'', the newly-created
|
|
binaries will be deposited in a directory tree identical to the
|
|
installed one, rooted at <tt>${DESTDIR}</tt>.
|
|
Some random combination of shared libraries modifications and
|
|
program rebuilds can cause this to fail in ``<tt/make world/'',
|
|
however.
|
|
|
|
<sect1>
|
|
<heading>
|
|
When my system boots, it says ``(bus speed defaulted)''.
|
|
</heading>
|
|
|
|
<p>The Adaptec 1542 SCSI host adapters allow the user to configure
|
|
their bus access speed in software. Previous versions of the
|
|
1542 driver tried to determine the fastest usable speed and set
|
|
the adapter to that. We found that this breaks some users'
|
|
systems, so you now have to define the ``<tt/TUNE_1542/'' kernel
|
|
configuration option in order to have this take place. Using it
|
|
on those systems where it works may make your disks run faster,
|
|
but on those systems where it doesn't, your data could be
|
|
corrupted.
|
|
|
|
<sect1>
|
|
<heading>
|
|
Can I follow current with limited Internet access?<label id="ctm">
|
|
</heading>
|
|
|
|
<p>Yes, you can do this <tt /without/ downloading the whole source tree
|
|
by using the <url url="../handbook/synching.html#CTM" name="CTM facility.">
|
|
|
|
<sect1>
|
|
<heading>How did you split the distribution into 240k files?</heading>
|
|
|
|
<p>Newer BSD based systems have a ``<tt/-b/'' option to split that
|
|
allows them to split files on arbitrary byte boundaries.
|
|
|
|
<p>Here is an example from <tt>/usr/src/Makefile</tt>.
|
|
|
|
<verb>
|
|
bin-tarball:
|
|
(cd ${DISTDIR}; \
|
|
tar cf - . \
|
|
gzip --no-name -9 -c | \
|
|
split -b 240640 - \
|
|
${RELEASEDIR}/tarballs/bindist/bin_tgz.)
|
|
</verb>
|
|
|
|
<sect1>
|
|
<heading>I've written a kernel extension, who do I send it to?</heading>
|
|
|
|
<p>Please take a look at <url url="../handbook/contrib.html"
|
|
name="The Handbook entry on how to submit code.">
|
|
|
|
<p>And thanks for the thought!
|
|
|
|
<sect1>
|
|
<heading>How are Plug N Play ISA cards detected and initialized?</heading>
|
|
|
|
<p>By: <url url="mailto:uhclem@nemesis.lonestar.org"
|
|
name="Frank Durda IV">
|
|
|
|
<p>In a nutshell, there a few I/O ports that all of the PnP boards
|
|
respond to when the host asks if anyone is out there. So when
|
|
the PnP probe routine starts, he asks if there are any PnP boards
|
|
present, and all the PnP boards respond with their model # to
|
|
a I/O read of the same port, so the probe routine gets a wired-OR
|
|
``yes'' to that question. At least one bit will be on in that
|
|
reply. Then the probe code is able to cause boards with board
|
|
model IDs (assigned by Microsoft/Intel) lower than X to go
|
|
``off-line''. It then looks to see if any boards are still
|
|
responding to the query. If the answer was ``<tt/0/'', then
|
|
there are no boards with IDs above X. Now probe asks if there
|
|
are any boards below ``X''. If so, probe knows there are boards
|
|
with a model numbers below X. Probe then asks for boards greater
|
|
than X-(limit/4) to go off-line. If repeats the query. By
|
|
repeating this semi-binary search of IDs-in-range enough times,
|
|
the probing code will eventually identify all PnP boards present
|
|
in a given machine with a number of iterations that is much lower
|
|
than what 2^64 would take.
|
|
|
|
<p>The IDs are two 32-bit fields (hence 2ˆ64) + 8 bit checksum.
|
|
The first 32 bits are a vendor identifier. They never come out
|
|
and say it, but it appears to be assumed that different types of
|
|
boards from the same vendor could have different 32-bit vendor
|
|
ids. The idea of needing 32 bits just for unique manufacturers
|
|
is a bit excessive.
|
|
|
|
<p>The lower 32 bits are a serial #, ethernet address, something
|
|
that makes this one board unique. The vendor must never produce
|
|
a second board that has the same lower 32 bits unless the upper
|
|
32 bits are also different. So you can have multiple boards of
|
|
the same type in the machine and the full 64 bits will still be
|
|
unique.
|
|
|
|
<p>The 32 bit groups can never be all zero. This allows the
|
|
wired-OR to show non-zero bits during the initial binary search.
|
|
|
|
<p>Once the system has identified all the board IDs present, it will
|
|
reactivate each board, one at a time (via the same I/O ports),
|
|
and find out what resources the given board needs, what interrupt
|
|
choices are available, etc. A scan is made over all the boards
|
|
to collect this information.
|
|
|
|
<p>This info is then combined with info from any ECU files on the
|
|
hard disk or wired into the MLB BIOS. The ECU and BIOS PnP
|
|
support for hardware on the MLB is usually synthetic, and the
|
|
peripherals don't really do genuine PnP. However by examining
|
|
the BIOS info plus the ECU info, the probe routines can cause the
|
|
devices that are PnP to avoid those devices the probe code cannot
|
|
relocate.
|
|
|
|
<p>Then the PnP devices are visited once more and given their I/O,
|
|
DMA, IRQ and Memory-map address assignments. The devices will
|
|
then appear at those locations and remain there until the next
|
|
reboot, although there is nothing that says you can't move them
|
|
around whenever you want.
|
|
|
|
<p>There is a lot of oversimplification above, but you should get
|
|
the general idea.
|
|
|
|
<p>Microsoft took over some of the primary printer status ports to
|
|
do PnP, on the logic that no boards decoded those addresses for
|
|
the opposing I/O cycles. I found a genuine IBM printer board
|
|
that did decode writes of the status port during the early PnP
|
|
proposal review period, but MS said ``tough''. So they do a
|
|
write to the printer status port for setting addresses, plus that
|
|
use that address + <tt/0x800/, and a third I/O port for reading
|
|
that can be located anywhere between <tt/0x200/ and <tt/0x3ff/.
|
|
|
|
<sect1>
|
|
<heading>Does FreeBSD support architectures other than the x86?</heading>
|
|
|
|
<p>Several groups of people have expressed interest in working on
|
|
multi-architecture ports for FreeBSD and the FreeBSD/AXP (ALPHA)
|
|
port is one such effort which has been quite successful, now
|
|
available in 3.0 SNAPshot release form at <url
|
|
url="ftp://ftp.FreeBSD.org/pub/FreeBSD/alpha/"
|
|
name="ftp://ftp.FreeBSD.org/pub/FreeBSD/alpha">. The ALPHA
|
|
port currently runs on a growing number of ALPHA machine
|
|
types, among them the AlphaStation, AXPpci, PC164, Miata and Multia
|
|
models. This port is not yet considered a full release and won't be
|
|
until a full compliment of system installation tools and a distribution
|
|
on CDROM installation media is available, including a reasonable
|
|
number of working ports and packages.
|
|
FreeBSD/AXP should be considered BETA quality software at this
|
|
time. For status information, please join the
|
|
<tt><freebsd-alpha@FreeBSD.org></tt><ref id="mailing"
|
|
name="mailing list">.
|
|
|
|
Interest has also been expressed in a port of FreeBSD to
|
|
the SPARC architecture, join the <tt><freebsd-sparc@FreeBSD.org>
|
|
</tt><ref id="mailing" name="mailing list"> if you are interested
|
|
in joining that project. For general discussion on new architectures,
|
|
join the <tt><freebsd-platforms@FreeBSD.org></tt>
|
|
<ref id="mailing" name="mailing list">.
|
|
|
|
<sect1>
|
|
<heading>I need a major number for a device driver I've written.</heading>
|
|
|
|
<p>This depends on whether or not you plan on making the driver
|
|
publicly available. If you do, then please send us a copy of the
|
|
driver source code, plus the appropriate modifications to
|
|
<tt>files.i386</tt>, a sample configuration file entry, and the
|
|
appropriate <htmlurl url="http://www.FreeBSD.org/cgi/man.cgi?MAKEDEV"
|
|
name="MAKEDEV"> code to create any special files your device uses. If
|
|
you do not, or are unable to because of licensing restrictions, then
|
|
character major number 32 and block major number 8 have been reserved
|
|
specifically for this purpose; please use them. In any case, we'd
|
|
appreciate hearing about your driver on
|
|
<tt><freebsd-hackers@FreeBSD.org></tt>.
|
|
|
|
|
|
<sect1>
|
|
<heading>Alternative layout policies for directories</heading>
|
|
|
|
<p>
|
|
In answer to the question of alternative layout policies for
|
|
directories, the scheme that is currently in use is unchanged
|
|
from what I wrote in 1983. I wrote that policy for the original
|
|
fast filesystem, and never revisited it. It works well at keeping
|
|
cylinder groups from filling up. As several of you have noted,
|
|
it works poorly for find. Most filesystems are created from
|
|
archives that were created by a depth first search (aka ftw).
|
|
These directories end up being striped across the cylinder groups
|
|
thus creating a worst possible senario for future depth first
|
|
searches. If one knew the total number of directories to be
|
|
created, the solution would be to create (total / fs_ncg) per
|
|
cylinder group before moving on. Obviously, one would have to
|
|
create some heuristic to guess at this number. Even using a
|
|
small fixed number like say 10 would make an order of magnitude
|
|
improvement. To differentiate restores from normal operation
|
|
(when the current algorithm is probably more sensible), you
|
|
could use the clustering of up to 10 if they were all done
|
|
within a ten second window. Anyway, my conclusion is that this
|
|
is an area ripe for experimentation.</p>
|
|
|
|
<p>Kirk McKusick, September 1998</p>
|
|
|
|
<sect1>
|
|
<heading>Making the most of a kernel panic</heading>
|
|
|
|
<p>
|
|
<em>[This section was extracted from a mail written by <url
|
|
url="mailto:wpaul@FreeBSD.org" name="Bill Paul"> on the
|
|
freebsd-current <ref id="mailing" name="mailing list"> by <url
|
|
url="mailto:des@FreeBSD.org" name="Dag-Erling Coïdan
|
|
Smørgrav">, who fixed a few typos and added the bracketed
|
|
comments]</em>
|
|
|
|
<p>
|
|
<verb>
|
|
From: Bill Paul <wpaul@skynet.ctr.columbia.edu>
|
|
Subject: Re: the fs fun never stops
|
|
To: ben@rosengart.com
|
|
Date: Sun, 20 Sep 1998 15:22:50 -0400 (EDT)
|
|
Cc: current@FreeBSD.org
|
|
</verb>
|
|
|
|
<p>
|
|
<em>[<ben@rosengart.com> posted the following panic
|
|
message]</em>
|
|
<verb>
|
|
> Fatal trap 12: page fault while in kernel mode
|
|
> fault virtual address = 0x40
|
|
> fault code = supervisor read, page not present
|
|
> instruction pointer = 0x8:0xf014a7e5
|
|
^^^^^^^^^^
|
|
> stack pointer = 0x10:0xf4ed6f24
|
|
> frame pointer = 0x10:0xf4ed6f28
|
|
> code segment = base 0x0, limit 0xfffff, type 0x1b
|
|
> = DPL 0, pres 1, def32 1, gran 1
|
|
> processor eflags = interrupt enabled, resume, IOPL = 0
|
|
> current process = 80 (mount)
|
|
> interrupt mask =
|
|
> trap number = 12
|
|
> panic: page fault
|
|
</verb>
|
|
|
|
<p> [When] you see a message like this, it's not enough to just
|
|
reproduce it and send it in. The instruction pointer value that
|
|
I highlighted up there is important; unfortunately, it's also
|
|
configuration dependent. In other words, the value varies
|
|
depending on the exact kernel image that you're using. If you're
|
|
using a GENERIC kernel image from one of the snapshots, then
|
|
it's possible for somebody else to track down the offending
|
|
function, but if you're running a custom kernel then only
|
|
<em/you/ can tell us where the fault occured.
|
|
|
|
<p> What you should do is this:
|
|
|
|
<itemize>
|
|
<item>Write down the instruction pointer value. Note that the
|
|
<tt/0x8:/ part at the begining is not significant in this case:
|
|
it's the <tt/0xf0xxxxxx/ part that we want.
|
|
<item>When the system reboots, do the following:
|
|
<verb>
|
|
% nm /kernel.that.caused.the.panic | grep f0xxxxxx
|
|
</verb>
|
|
where <tt/f0xxxxxx/ is the instruction pointer value. The
|
|
odds are you will not get an exact match since the symbols
|
|
in the kernel symbol table are for the entry points of
|
|
functions and the instruction pointer address will be
|
|
somewhere inside a function, not at the start. If you don't
|
|
get an exact match, omit the last digit from the instruction
|
|
pointer value and try again, i.e.:
|
|
<verb>
|
|
% nm /kernel.that.caused.the.panic | grep f0xxxxx
|
|
</verb>
|
|
If that doesn't yield any results, chop off another digit.
|
|
Repeat until you get some sort of output. The result will be
|
|
a possible list of functions which caused the panic. This is
|
|
a less than exact mechanism for tracking down the point of
|
|
failure, but it's better than nothing.
|
|
</itemize>
|
|
|
|
<p> I see people constantly show panic messages like this but
|
|
rarely do I see someone take the time to match up the
|
|
instruction pointer with a function in the kernel symbol table.
|
|
|
|
<p> The best way to track down the cause of a panic is by
|
|
capturing a crash dump, then using <tt/gdb(1)/ to to a stack
|
|
trace on the crash dump. Of course, this depends on <tt/gdb(1)/
|
|
in -current working correctly, which I can't guarantee (I recall
|
|
somebody saying that the new ELF-ized <tt/gdb(1)/ didn't handle
|
|
kernel crash dumps correctly: somebody should check this before
|
|
3.0 goes out of beta or there'll be a lot of red faces after the
|
|
CDs ship).
|
|
|
|
<p>
|
|
In any case, the method I normally use is this:
|
|
|
|
<itemize>
|
|
<item>Set up a kernel config file, optionally adding 'options DDB' if you
|
|
think you need the kernel debugger for something. (I use this mainly
|
|
for setting beakpoints if I suspect an infinite loop condition of
|
|
some kind.)
|
|
<item>Use <tt/config -g KERNELCONFIG/ to set up the build directory.
|
|
<item><tt>cd /sys/compile/KERNELCONFIG; make</tt>
|
|
<item>Wait for kernel to finish compiling.
|
|
<item><tt/cp kernel kernel.debug/
|
|
<item><tt/strip -d kernel/
|
|
<item><tt/mv /kernel /kernel.orig/
|
|
<item><tt>cp kernel /</tt>
|
|
<item>reboot
|
|
</itemize>
|
|
|
|
<p> <em>[Note: Now that FreeBSD 3.x kernels are Elf by default,
|
|
you should use <tt/strip -g/ instead of <tt/strip -d/. If for some
|
|
reason your kernel is still a.out, use <tt/strip -aout -d/.]</em>
|
|
|
|
<p> Note that YOU DO <em/NOT/ WANT TO ACTUALLY BOOT THE KERNEL
|
|
WITH ALL THE DEBUG SYMBOLS IN IT. A kernel compiled with <tt/-g/
|
|
can easily be close to 10MB in size. You don't have to actually
|
|
boot this massive image: you only need it later for <tt/gdb(1)/
|
|
(<tt/gdb(1)/ wants the symbol table). Instead, you want to keep
|
|
a copy of the full image and create a second image with the
|
|
debug symbols stripped out using <tt/strip -d/. It is this
|
|
second stripped image that you want to boot.
|
|
|
|
<p> To make sure you capture a crash dump, you need edit
|
|
<tt>/etc/rc.conf</tt> and set <tt/dumpdev/ to point to your swap
|
|
partition. This will cause the <tt/rc(8)/ scripts to use the
|
|
<tt/dumpon(8)/ command to enable crash dumps. You can also run
|
|
<tt/dumpon(8)/ manually. After a panic, the crash dump can be
|
|
recovered using <tt/savecore(8)/; if <tt/dumpdev/ is set in
|
|
<tt>/etc/rc.conf</tt>, the <tt/rc(8)/ scripts will run
|
|
<tt/savecore(8)/ automatically and put the crash dump in
|
|
<tt>/var/crash</tt>.
|
|
|
|
<p> NOTE: FreeBSD crash dumps are usually the same size as the
|
|
physical RAM size of your machine. That is, if you have 64MB of
|
|
RAM, you will get a 64MB crash dump. Therefore you must make sure
|
|
there's enough space in <tt>/var/crash</tt> to hold the dump.
|
|
Alternatively, you run <tt/savecore(8)/ manually and have it
|
|
recover the crash dump to another directory where you have more
|
|
room. It's possible to limit the size of the crash dump by using
|
|
<tt/options MAXMEM=(foo)/ to set the amount of memory the kernel
|
|
will use to something a little more sensible. For example, if
|
|
you have 128MB of RAM, you can limit the kernel's memory usage
|
|
to 16MB so that your crash dump size will be 16MB instead of
|
|
128MB.
|
|
|
|
<p> Once you have recovered the crash dump, you can get a stack
|
|
trace with <tt/gdb(1)/ as follows:
|
|
|
|
<p>
|
|
<verb>
|
|
% gdb -k /sys/compile/KERNELCONFIG/kernel.debug /var/crash/vmcore.0
|
|
(gdb) where
|
|
</verb>
|
|
|
|
<p> Note that there may be several screens worth of information;
|
|
ideally you should use <tt/script(1)/ to capture all of them.
|
|
Using the unstripped kernel image with all the debug symbols
|
|
should show the exact line of kernel source code where the panic
|
|
occured. Usually you have to read the stack trace from the
|
|
bottom up in order to trace the exact sequence of events that
|
|
lead to the crash. You can also use <tt/gdb(1)/ to print out the
|
|
contents of various variables or structures in order to examine
|
|
the system state at the time of the crash.
|
|
|
|
<p> Now, if you're really insane and have a second computer, you
|
|
can also configure <tt/gdb(1)/ to do remote debugging such that
|
|
you can use <tt/gdb(1)/ on one system to debug the kernel on
|
|
another system, including setting breakpoints, single-stepping
|
|
through the kernel code, just like you can do with a normal
|
|
user-mode program. I haven't played with this yet as I don't
|
|
often have the chance to set up two machines side by side for
|
|
debugging purposes.
|
|
|
|
<p> <em>[Bill adds: "I forgot to mention one thing: if you have
|
|
DDB enabled and the kernel drops into the debugger, you can
|
|
force a panic (and a crash dump) just by typing 'panic' at the
|
|
ddb prompt. It may stop in the debugger again during the panic
|
|
phase. If it does, type 'continue' and it will finish the crash
|
|
dump." -ed]</em>
|
|
|
|
<sect1>
|
|
<heading>dlsym() stopped working for ELF executables!</heading>
|
|
|
|
<p>The ELF toolchain does not, by default, make the symbols
|
|
defined in an executable visible to the dynamic linker.
|
|
Consequently <tt>dlsym()</tt> searches on handles obtained
|
|
from calls to <tt>dlopen(NULL, flags)</tt> will fail to find
|
|
such symbols.
|
|
|
|
<p>If you want to search, using <tt>dlsym()</tt>, for symbols
|
|
present in the main executable of a process, you need to link
|
|
the executable using the <tt>-export-dynamic</tt> option to the
|
|
<htmlurl url="http://www.FreeBSD.org/cgi/man.cgi?ld"
|
|
name="ELF linker">.
|
|
|
|
|
|
<sect1>
|
|
<heading>Increasing or reducing the kernel address space</heading>
|
|
|
|
<p>
|
|
By default, the kernel address space is 256 MB on FreeBSD 3.x
|
|
and 1 GB on FreeBSD 4.x. If you run a network-intensive server
|
|
(e.g. a large FTP or HTTP server), you might find that 256 MB is
|
|
not enough.
|
|
|
|
<p>
|
|
So how do you increase the address space? There are two aspects
|
|
to this. First, you need to tell the kernel to reserve a larger
|
|
portion of the address space for itself. Second, since the
|
|
kernel is loaded at the top of the address space, you need to
|
|
lower the load address so it doesn't bump its head against the
|
|
ceiling.
|
|
|
|
<p>
|
|
The first goal is achieved by increasing the value of
|
|
<tt/NKPDE/ in <tt>src/sys/i386/include/pmap.h</tt>. Here's what
|
|
it looks like for a 1 GB address space:
|
|
|
|
<verb>
|
|
#ifndef NKPDE
|
|
#ifdef SMP
|
|
#define NKPDE 254 /* addressable number of page tables/pde's */
|
|
#else
|
|
#define NKPDE 255 /* addressable number of page tables/pde's */
|
|
#endif /* SMP */
|
|
#endif
|
|
</verb>
|
|
|
|
<p>
|
|
To find the correct value of <tt/NKPDE/, divide the desired
|
|
address space size (in megabytes) by four, then subtract one for
|
|
UP and two for SMP.
|
|
|
|
<p>
|
|
To achieve the second goal, you need to compute the correct load
|
|
address: simply subtract the address space size (in bytes) from
|
|
0x100100000; the result is 0xc0100000 for a 1 GB address space.
|
|
Set <tt/LOAD_ADDRESS/ in <tt>src/sys/i386/conf/Makefile.i386</tt>
|
|
to that value; then set the location counter in the beginning of
|
|
the section listing in <tt>src/sys/i386/conf/kernel.script</tt>
|
|
to the same value, as follows:
|
|
|
|
<verb>
|
|
OUTPUT_FORMAT("elf32-i386", "elf32-i386", "elf32-i386")
|
|
OUTPUT_ARCH(i386)
|
|
ENTRY(btext)
|
|
SEARCH_DIR(/usr/lib); SEARCH_DIR(/usr/obj/elf/home/src/tmp/usr/i386-unknown-freebsdelf/lib);
|
|
SECTIONS
|
|
{
|
|
/* Read-only sections, merged into text segment: */
|
|
. = 0xc0100000 + SIZEOF_HEADERS;
|
|
.interp : { *(.interp) }
|
|
</verb>
|
|
|
|
<p>
|
|
Then reconfig and rebuild your kernel. You will probably have
|
|
problems with <tt/ps(1)/, <tt/top(1)/ and the like; <tt/make
|
|
world/ should take care of it (or a manual rebuild of
|
|
<tt/libkvm/, <tt/ps/ and <tt/top/ after copying the patched
|
|
<tt/pmap.h/ to <tt>/usr/include/vm/</tt>.
|
|
|
|
<p>
|
|
NOTE: the size of the kernel address space must be a multiple of
|
|
four megabytes.
|
|
|
|
<p>
|
|
[<url url="mailto:dg@FreeBSD.org" name="David Greenman">
|
|
adds: <em> I think the kernel address space needs to be a power
|
|
of two, but I'm not certain about that. The old(er) boot code
|
|
used to monkey with the high order address bits and I think
|
|
expected at least 256MB granularity.]</em>
|
|
|
|
</sect>
|