e8432ac802
We have some very fancy min/max macros that have tons of sanity checking to warn about mixed signedness etc. This is all things that a sane compiler should warn about, but there are no sane compiler interfaces for this, and '-Wsign-compare' is broken [1] and not useful. So then we compensate (some would say over-compensate) by doing the checks manually with some truly horrid macro games. And no, we can't just use __builtin_types_compatible_p(), because the whole question of "does it make sense to compare these two values" is a lot more complicated than that. For example, it makes a ton of sense to compare unsigned values with simple constants like "5", even if that is indeed a signed type. So we have these very strange macros to try to make sensible type checking decisions on the arguments to 'min()' and 'max()'. But that can cause enormous code expansion if the min()/max() macros are used with complicated expressions, and particularly if you nest these things so that you get the first big expansion then expanded again. The xen setup.c file ended up ballooning to over 50MB of preprocessed noise that takes 15s to compile (obviously depending on the build host), largely due to one single line. So let's split that one single line to just be simpler. I think it ends up being more legible to humans too at the same time. Now that single file compiles in under a second. Reported-and-reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Link: https://lore.kernel.org/all/c83c17bb-be75-4c67-979d-54eee38774c6@lucifer.local/ Link: https://staticthinking.wordpress.com/2023/07/25/wsign-compare-is-garbage/ [1] Cc: David Laight <David.Laight@aculab.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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 reStructuredText 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.