This page provides patches that extend the Linux kernel to
support the Pentium III Streaming SIMD Extensions.
Intel's Pentium III processor contains some new instructions and
registers, known collectively as the Streaming SIMD Extensions (SSE),
which increase the Pentium III's floating-point performance. With
the proper attention from the programmer, the Streaming SIMD
Extensions allow the Pentium III to handle floating-point-intensive
applications like video and audio handling, 3-D modeling, and
physical simulations much more quickly than its predecessors.
In a multi-tasking environment, the Streaming SIMD Extensions
require support from the operating system: the SIMD registers must be
handled properly by the operating system's context switching code.
When the system switches control from one process to another, the old
process's SIMD registers must be saved away, and the saved values of
the new process's SIMD registers must be loaded into the processor.
The Pentium III processor prohibits programs from using the Streaming
SIMD Extensions unless the operating system tells the processor at
system startup time that it is aware of the SIMD registers, and will
manage them properly.
The patch available on this page is based on the Pentium III patch
provided by Doug Ledford, available from his Linux
Kernel Patch Page.
There are two versions of the kernel patch: one for Linux 2.2.5,
and one for Linux 2.2.12. (These are the versions distributed with
Red Hat Linux 6.0 and 6.1.) When I wrote the patches, the basic SSE
support had not yet appeared in the experimental 2.3 kernel series, so
I was unable to produce a patch against a more recent kernel version.
However, as soon as the SSE support does appear, I will produce a new
set of patches for the debugging support.
There are four basic steps to applying the patches. In summary:
- Build a kernel from the unmodified sources, and test it.
-
It is essential to verify that you can build a kernel
straight from the sources, install it, and boot it up successfully,
before you apply any patches whatsoever. Now is also a good time to
select the right set of drivers and modules, etc.
This is your best opportunity to distinguish between problems
due to the patch, and problems due to the kernel configuration. I had a
hard time getting everything going at first, and needed help from
someone with more experience. The last thing you want to worry about
here are more random external influences, like patches from strangers.
Red Hat Linux includes instructions for building a custom
kernel in the Red Hat reference guide (the book you got with your
distribution). In the Red Hat 6.1 distribution, look at section 2.8,
``Building a Custom Kernel''. If you are unpacking your sources from an
RPM, make sure to execute the RPM's %prep stage, to apply
whatever patches are needed for your distribution.
Make sure that you are actually running the kernel you
compiled. Put a new call to printk some place safe, like the calibrate_delay
function in init/main.c, and verify that your kernel prints
it out when it boots up. (You might find the dmesg command
helpful here.)
Make sure that you have recompiled and installed your kernel
modules. If the boot process hangs after it says ``Finding module
dependencies'', one possibility is that you're trying to run your new
kernel with your old modules.
If you ask me for help, and I find out that you haven't gotten
a straight kernel build working before getting in touch with me, I'm
going to be annoyed. There are lots of people out there who have more
experience building kernels than I do, so you should find a friend who
knows this stuff and get their help.
- Apply the kernel patches.
-
First of all, use your web browser to download the kernel patch
to a file somewhere convenient. There are two separate patches: one for
version 2.2.5 of the Linux kernel:
http://sourceware.cygnus.com/gdb/papers/linux/jimb.linux-2.2.5-sse-ptrace-2.patch
and one for version 2.2.12 of the kernel:
http://sourceware.cygnus.com/gdb/papers/linux/jimb.linux-2.2.12-sse-ptrace-2.patch
In these instructions, I assume you're using the 2.2.12 patch, but the
procedure is the same for the 2.2.5 patch; only the patch's filename is
different.
Now, cd to the top directory of your kernel source tree --- the
one that contains the files README.kernel-sources, REPORTING-BUGS,
and so on.
$ cd /usr/src/linux
$
Use the patch command to apply the patch file to the
sources, as shown here:
$ patch -p0 < ~/incoming/jimb.linux-2.2.12-sse-ptrace-2.patch
patching file `Documentation/Configure.help'
patching file `arch/i386/Makefile'
patching file `arch/i386/config.in'
patching file `arch/i386/kernel/head.S'
patching file `arch/i386/kernel/i386_ksyms.c'
patching file `arch/i386/kernel/process.c'
patching file `arch/i386/kernel/ptrace.c'
patching file `arch/i386/kernel/setup.c'
patching file `arch/i386/kernel/signal.c'
patching file `arch/i386/kernel/smp.c'
patching file `arch/i386/kernel/traps.c'
patching file `arch/i386/lib/Makefile'
patching file `arch/i386/lib/simd.c'
patching file `arch/i386/lib/usercopy.c'
patching file `arch/i386/mm/init.c'
patching file `fs/binfmt_elf.c'
patching file `include/asm-i386/bugs.h'
patching file `include/asm-i386/i387.h'
patching file `include/asm-i386/processor.h'
patching file `include/asm-i386/ptrace.h'
patching file `include/asm-i386/string.h'
patching file `include/asm-i386/uaccess.h'
patching file `include/linux/elf.h'
$
- Configure the kernel to enable the SSE support.
-
There are several different ways to configure a Linux kernel;
these are generic instructions, which should work for any of the
configuration methods.
In the category ``Processor type and features'':
- Select a CPU type of ``PPro/6x86MX/PII'' or
``PIII/Xeon/Deschutes''.
- Select ``Enable PII/PIII Extended/Fast CPU save and restore
support''.
- Select ``Enable PIII Streaming XMM operations''.
Leave the rest of the configuration the way it was for your
previous working build. (You do have a previous working build, don't
you?)
- Build your patched kernel.
-
Use the same process here you did for your previous working
build.
- Install your kernel.
-
As before, make sure you have built and installed fresh
modules, to go along with your kernel. Trying to use old modules with a
new kernel doesn't work too well. If your kernel hangs while booting,
after saying ``Finding module dependencies'', then you may not have
installed your new modules the way you expected.
Make sure to leave a kernel you know is useable in your /etc/lilo.conf
file, so if things blow up, you have something to fall back to. Once
you've got it working, however, you can make your new kernel the
default; see the lilo.conf(5) for more info here.
- Reboot, using the new kernel.
-
When the lilo: prompt appears during the boot
process, type the name you gave your patched kernel in /etc/lilo.conf.
- Verify that your kernel supports the Streaming SIMD Extensions
-
The file /proc/cpuinfo contains a list of the
CPU-related options you selected when you configured the kernel. If the
Streaming SIMD Extensions support is enabled, the line labeled flags:
should contain the words fxsr and xmm, usually at
the end. For example:
$ cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 7
model name : Pentium III (Katmai)
stepping : 2
cpu MHz : 497.440714
cache size : 512 KB
fdiv_bug : no
hlt_bug : no
sep_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 2
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 sep mtrr pge mca cmov pat pse36 mmx fxsr xmm
bogomips : 496.44
$
- Patch your header files.
-
Among other things, the kernel patch extends some system calls
to give the debugger access to processes' SIMD registers. However, we
need to extend the user-side descriptions of these system calls to
include the new functionality.
So, use your web browser to download the header file patch to
somewhere convenient. In these instructions, I assume you're using the
same filename I did: jimb.glibc-sse-ptrace.patch.
The URL for the patch is http://sourceware.cygnus.com/gdb/papers/linux/jimb.glibc-sse-ptrace.patch.
Now, cd to /usr/include/sys --- the directory
containing ptrace.h and user.h.
These files are not usually world-writeable, so, as root, use
the patch command to apply the patch file to the sources, as
shown here:
$ cd /usr/include/sys
$ su
Password:
[EMAIL PROTECTED] sys]# patch -p0 < ~jimb/incoming/jimb.glibc-sse-ptrace.patch
patching file `ptrace.h'
patching file `user.h'
[EMAIL PROTECTED] sys]# exit
$
You don't need to rebuild your kernel after applying this
patch. It's only interesting to debuggers.
- Make sure you have the right sources for GDB.
-
We added support for the Streaming SIMD Extensions to GDB
rather recently. To verify that your GDB sources contain this support,
look in gdb/ChangeLog. There should be an entry no earlier
than November 1999 containing the text:
Add support for SSE registers in core files.
* corelow.c (get_core_register_section): New function.
If the file contains these comments, then your GDB sources
should support the Streaming SIMD Extensions.
- Configure and build GDB.
-
GDB's configuration process checks your system's header files
to see whether your system has been extended to support the Streaming
SIMD Extensions. So, you must configure GDB after patching your header
files. Follow the instructions in the README file at the top of the
source tree, or the instructions you received from Cygnus.
- Verify that your GDB has been built properly.
-
Start up the GDB you just built, and try to print the value of
the SIMD register $xmm0. Since you're not actually debugging
a program, GDB doesn't have any value to display for that register, but
it should at least recognize that it is a register name:
$ /umbra/jimb/build/gdb/gdb -nw
GNU gdb 4.18-PentiumIII-991112
Copyright 1998 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions. This version of GDB is supported
for customers of Cygnus Solutions. Type "show warranty" for details.
This GDB was configured as "i686-pc-linux-gnu".
(gdb) print $xmm0
No registers.
(gdb) print $foo
$1 = void
(gdb)
As you can see, this GDB says that an undefined convenience
variable is void, but recognizes that $xmm0 is the
name of a register.
Of course, the final test is to try to debug a program that
uses the Streaming SIMD Extensions, either at the source level using
the Intel intrinsics interface, or at the assembly language level.
If you have any trouble with the patch or with these directions,
please send mail to me, Jim Blandy <[EMAIL PROTECTED]>.
