mirror of https://gitee.com/openkylin/linux.git
36126f8f2e
This changes the interfaces in <asm/word-at-a-time.h> to be a bit more complicated, but a lot more generic. In particular, it allows us to really do the operations efficiently on both little-endian and big-endian machines, pretty much regardless of machine details. For example, if you can rely on a fast population count instruction on your architecture, this will allow you to make your optimized <asm/word-at-a-time.h> file with that. NOTE! The "generic" version in include/asm-generic/word-at-a-time.h is not truly generic, it actually only works on big-endian. Why? Because on little-endian the generic algorithms are wasteful, since you can inevitably do better. The x86 implementation is an example of that. (The only truly non-generic part of the asm-generic implementation is the "find_zero()" function, and you could make a little-endian version of it. And if the Kbuild infrastructure allowed us to pick a particular header file, that would be lovely) The <asm/word-at-a-time.h> functions are as follows: - WORD_AT_A_TIME_CONSTANTS: specific constants that the algorithm uses. - has_zero(): take a word, and determine if it has a zero byte in it. It gets the word, the pointer to the constant pool, and a pointer to an intermediate "data" field it can set. This is the "quick-and-dirty" zero tester: it's what is run inside the hot loops. - "prep_zero_mask()": take the word, the data that has_zero() produced, and the constant pool, and generate an *exact* mask of which byte had the first zero. This is run directly *outside* the loop, and allows the "has_zero()" function to answer the "is there a zero byte" question without necessarily getting exactly *which* byte is the first one to contain a zero. If you do multiple byte lookups concurrently (eg "hash_name()", which looks for both NUL and '/' bytes), after you've done the prep_zero_mask() phase, the result of those can be or'ed together to get the "either or" case. - The result from "prep_zero_mask()" can then be fed into "find_zero()" (to find the byte offset of the first byte that was zero) or into "zero_bytemask()" (to find the bytemask of the bytes preceding the zero byte). The existence of zero_bytemask() is optional, and is not necessary for the normal string routines. But dentry name hashing needs it, so if you enable DENTRY_WORD_AT_A_TIME you need to expose it. This changes the generic strncpy_from_user() function and the dentry hashing functions to use these modified word-at-a-time interfaces. This gets us back to the optimized state of the x86 strncpy that we lost in the previous commit when moving over to the generic version. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
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| .. | ||
| boot | ||
| configs | ||
| include/asm | ||
| kernel | ||
| lib | ||
| mm | ||
| Kconfig | ||
| Makefile | ||
| README.openrisc | ||
| TODO.openrisc | ||
README.openrisc
OpenRISC Linux
==============
This is a port of Linux to the OpenRISC class of microprocessors; the initial
target architecture, specifically, is the 32-bit OpenRISC 1000 family (or1k).
For information about OpenRISC processors and ongoing development:
website http://openrisc.net
For more information about Linux on OpenRISC, please contact South Pole AB.
email: info@southpole.se
website: http://southpole.se
http://southpoleconsulting.com
---------------------------------------------------------------------
Build instructions for OpenRISC toolchain and Linux
===================================================
In order to build and run Linux for OpenRISC, you'll need at least a basic
toolchain and, perhaps, the architectural simulator. Steps to get these bits
in place are outlined here.
1) The toolchain can be obtained from openrisc.net. Instructions for building
a toolchain can be found at:
http://openrisc.net/toolchain-build.html
2) or1ksim (optional)
or1ksim is the architectural simulator which will allow you to actually run
your OpenRISC Linux kernel if you don't have an OpenRISC processor at hand.
git clone git://openrisc.net/jonas/or1ksim-svn
cd or1ksim
./configure --prefix=$OPENRISC_PREFIX
make
make install
3) Linux kernel
Build the kernel as usual
make ARCH=openrisc defconfig
make ARCH=openrisc
4) Run in architectural simulator
Grab the or1ksim platform configuration file (from the or1ksim source) and
together with your freshly built vmlinux, run your kernel with the following
incantation:
sim -f arch/openrisc/or1ksim.cfg vmlinux
---------------------------------------------------------------------
Terminology
===========
In the code, the following particles are used on symbols to limit the scope
to more or less specific processor implementations:
openrisc: the OpenRISC class of processors
or1k: the OpenRISC 1000 family of processors
or1200: the OpenRISC 1200 processor
---------------------------------------------------------------------
History
========
18. 11. 2003 Matjaz Breskvar (phoenix@bsemi.com)
initial port of linux to OpenRISC/or32 architecture.
all the core stuff is implemented and seams usable.
08. 12. 2003 Matjaz Breskvar (phoenix@bsemi.com)
complete change of TLB miss handling.
rewrite of exceptions handling.
fully functional sash-3.6 in default initrd.
a much improved version with changes all around.
10. 04. 2004 Matjaz Breskvar (phoenix@bsemi.com)
alot of bugfixes all over.
ethernet support, functional http and telnet servers.
running many standard linux apps.
26. 06. 2004 Matjaz Breskvar (phoenix@bsemi.com)
port to 2.6.x
30. 11. 2004 Matjaz Breskvar (phoenix@bsemi.com)
lots of bugfixes and enhancments.
added opencores framebuffer driver.
09. 10. 2010 Jonas Bonn (jonas@southpole.se)
major rewrite to bring up to par with upstream Linux 2.6.36