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3e7e5baaab
Intel kernel bot triggered the build bug on ARC architecture that
in fact is as follows:
DECLARE_BITMAP(bitmap, BITS_PER_LONG);
bitmap_clear(bitmap, 0, BITS_PER_LONG);
BUILD_BUG_ON(!__builtin_constant_p(*bitmap));
which can be expanded to:
unsigned long bitmap[1];
memset(bitmap, 0, sizeof(*bitmap));
BUILD_BUG_ON(!__builtin_constant_p(*bitmap));
In most cases, a compiler is able to expand small/simple mem*()
calls to simple assignments or bitops, in this case that would mean:
unsigned long bitmap[1] = { 0 };
BUILD_BUG_ON(!__builtin_constant_p(*bitmap));
and on most architectures this works, but not on ARC, despite having
-O3 for every build.
So, to make this work, in case when the last bit to modify is still
within the first long (small_const_nbits()), just use plain
assignments for the rest of bitmap_*() functions which still use
mem*(), but didn't receive such compile-time optimizations yet.
This doesn't have the same coverage as compilers provide, but at
least something to start:
text: add/remove: 3/7 grow/shrink: 43/78 up/down: 1848/-3370 (-1546)
data: add/remove: 1/11 grow/shrink: 0/8 up/down: 4/-356 (-352)
notably cpumask_*() family when NR_CPUS <= BITS_PER_LONG:
netif_get_num_default_rss_queues 38 4 -34
cpumask_copy 90 - -90
cpumask_clear 146 - -146
and the abovementioned assertion started passing.
Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.com>
Signed-off-by: Yury Norov <yury.norov@gmail.com>
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.