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Maciej W. Rozycki 84aa85108b MIPS: Rewrite `csum_tcpudp_nofold' in plain C 
Recent commit 198688edbf ("MIPS: Fix inline asm input/output type
mismatch in checksum.h used with Clang") introduced a code size and
performance regression with 64-bit code emitted for `csum_tcpudp_nofold'
by GCC, caused by a redundant truncation operation produced due to a
data type change made to the variable associated with the inline
assembly's output operand.

The intent previously expressed here with operands and constraints for
optimal code was to have the output operand share a register with one
inputs, both of a different integer type each.  This is perfectly valid
with the MIPS psABI where a register can hold integer data of different
types and the assembly code used here makes data stored in the output
register match the data type used with the output operand, however it
has turned out impossible to express this arrangement in source code
such as to satisfy LLVM, apparently due to the compiler's internal
limitations.

There is nothing peculiar about the inline assembly `csum_tcpudp_nofold'
includes however, though it does choose assembly instructions carefully.

Rewrite this piece of assembly in plain C then, using corresponding C
language operations, making GCC produce the same assembly instructions,
possibly shuffled, in the general case and sometimes actually fewer of
them where an input is constant, because the compiler does not have to
reload it to a register (operand constraints could be adjusted for that,
but the plain C approach is cleaner anyway).

Example code size changes are as follows, for a 32-bit configuration:

      text       data        bss      total filename
   5920480    1347236     126592    7394308 vmlinux-old
   5920480    1347236     126592    7394308 vmlinux-now
   5919728    1347236     126592    7393556 vmlinux-c

and for a 64-bit configuration:

      text       data        bss      total filename
   6024112    1790828     225728    8040668 vmlinux-old
   6024128    1790828     225728    8040684 vmlinux-now
   6023760    1790828     225728    8040316 vmlinux-c

respectively, where "old" is with the commit referred reverted, "now" is
with no change, and "c" is with this change applied.

Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
2022-05-23 11:29:59 +02:00
arch MIPS: Rewrite `csum_tcpudp_nofold' in plain C 2022-05-23 11:29:59 +02:00
block block: don't print I/O error warning for dead disks 2022-04-15 06:33:03 -06:00
certs Kbuild updates for v5.18 2022-03-31 11:59:03 -07:00
crypto for-5.18/64bit-pi-2022-03-25 2022-03-26 12:01:35 -07:00
Documentation Devicetree fixes for v5.18, part 2: 2022-04-16 17:07:50 -07:00
drivers MIPS: Loongson: Use hwmon_device_register_with_groups() to register hwmon 2022-05-12 17:58:05 +02:00
fs Merge branch 'akpm' (patches from Andrew) 2022-04-15 15:57:18 -07:00
include gpio fixes for v5.18-rc3 2022-04-16 17:01:43 -07:00
init Kbuild updates for v5.18 2022-03-31 11:59:03 -07:00
ipc fs: allocate inode by using alloc_inode_sb() 2022-03-22 15:57:03 -07:00
kernel A small set of fixes for the timers core: 2022-04-17 09:53:01 -07:00
lib Driver core changes for 5.18-rc2 2022-04-10 09:55:09 -10:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm mm: kmemleak: take a full lowmem check in kmemleak_*_phys() 2022-04-15 14:49:56 -07:00
net Networking fixes for 5.18-rc3, including fixes from wireless and 2022-04-14 11:58:19 -07:00
samples dma-mapping updates for Linux 5.18 2022-03-29 08:50:14 -07:00
scripts hardening fixes for v5.18-rc3 2022-04-12 14:29:40 -10:00
security hardening updates for v5.18-rc1-fix1 2022-03-31 11:43:01 -07:00
sound sound fixes for 5.18-rc3 2022-04-14 11:08:12 -07:00
tools selftests/ftrace: Save kprobe_events to test log 2022-05-12 18:00:33 +02:00
usr Kbuild updates for v5.18 2022-03-31 11:59:03 -07:00
virt KVM/arm64 fixes for 5.18, take #1 2022-04-08 12:30:04 -04:00
.clang-format genirq/msi: Make interrupt allocation less convoluted 2021-12-16 22:22:20 +01:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: update Vasily Averin's email address 2022-04-08 14:20:36 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: replace a Microchip AT91 maintainer 2022-02-09 11:30:01 +01:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS ARM: SoC fixes for 5.18, part 2 2022-04-16 16:51:39 -07:00
Makefile Linux 5.18-rc3 2022-04-17 13:57:31 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.