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ab6b1010da
On recent (v6.6+) builds with Clang (based on Clang 18.0.0) and certain
configurations [0], I'm finding that (lack of) inlining decisions may
lead to section mismatch warnings like the following:
WARNING: modpost: vmlinux.o: section mismatch in reference:
cpumask_andnot (section: .text) ->
cpuhp_bringup_cpus_parallel.tmp_mask (section: .init.data) ERROR:
modpost: Section mismatches detected.
or more confusingly:
WARNING: modpost: vmlinux: section mismatch in reference:
cpumask_andnot+0x5f (section: .text) -> efi_systab_phys (section:
.init.data)
The first warning makes a little sense, because
cpuhp_bringup_cpus_parallel() (an __init function) calls
cpumask_andnot() on tmp_mask (an __initdata symbol). If the compiler
doesn't inline cpumask_andnot(), this may appear like a mismatch.
The second warning makes less sense, but might be because efi_systab_phys
and cpuhp_bringup_cpus_parallel.tmp_mask are laid out near each other,
and the latter isn't a proper C symbol definition.
In any case, it seems a reasonable solution to suggest more strongly to
the compiler that these cpumask macros *must* be inlined, as 'inline' is
just a recommendation.
This change has been previously proposed in the past as:
Subject: [PATCH 1/3] bitmap: switch from inline to __always_inline
https://lore.kernel.org/all/20221027043810.350460-2-yury.norov@gmail.com/
But the change has been split up, to separately justify the cpumask
changes (which drive my work) and the bitmap/const optimizations (that
Yury separately proposed for other reasons). This ends up as somewhere
between a "rebase" and "rewrite" -- I had to rewrite most of the patch.
According to bloat-o-meter, vmlinux decreases minimally in size (-0.00%
to -0.01%, depending on the version of GCC or Clang and .config in
question) with this series of changes:
gcc 13.2.0, x86_64_defconfig
-3005 bytes, Before=21944501, After=21941496, chg -0.01%
clang 16.0.6, x86_64_defconfig
-105 bytes, Before=22571692, After=22571587, chg -0.00%
gcc 9.5.0, x86_64_defconfig
-1771 bytes, Before=21557598, After=21555827, chg -0.01%
clang 18.0_pre516547 (ChromiumOS toolchain), x86_64_defconfig
-191 bytes, Before=22615339, After=22615148, chg -0.00%
clang 18.0_pre516547 (ChromiumOS toolchain), based on ChromiumOS config + gcov
-979 bytes, Before=76294783, After=76293804, chg -0.00%
[0] CONFIG_HOTPLUG_PARALLEL=y ('select'ed for x86 as of [1]) and
CONFIG_GCOV_PROFILE_ALL.
[1] commit
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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.