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Arnd Bergmann
0652035a57
In theory, compilers should be able to work this out themselves so we can use a simpler version based on the swab() helpers. I have verified that this works on all supported compiler versions (gcc-4.9 and up, clang-10 and up). Looking at the object code produced by gcc-11, I found that the impact is mostly a change in inlining decisions that lead to slightly larger code. In other cases, this version produces explicit byte swaps in place of separate byte access, or comparing against pre-swapped constants. While the source code is clearly simpler, I have not seen an indication of the new version actually producing better code on Arm, so maybe we want to skip this after all. From what I can tell, gcc recognizes the byteswap pattern in the byteshift.h header and can turn it into explicit instructions, but it does not turn a __builtin_bswap32() back into individual bytes when that would result in better output, e.g. when storing a byte-reversed constant. Suggested-by: Linus Torvalds <[email protected]> Signed-off-by: Arnd Bergmann <[email protected]>
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.