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BITS_PER_LONG does not exist in UAPI headers, so can't be used by the UAPI
__GENMASK(). Instead __BITS_PER_LONG needs to be used.
When __GENMASK() was introduced in commit 3c7a8e190bc5 ("uapi: introduce uapi-friendly macros for GENMASK"),
the code was fine. A broken revert in 1e7933a575ed ("uapi: Revert "bitops: avoid integer overflow in GENMASK(_ULL)"")
introduced the incorrect usage of BITS_PER_LONG.
That was fixed in commit 11fcf368506d ("uapi: bitops: use UAPI-safe variant of BITS_PER_LONG again").
But a broken sync of the kernel headers with the tools/ headers in
commit fc92099902fb ("tools headers: Synchronize linux/bits.h with the kernel sources")
undid the fix.
Reapply the fix and while at it also fix the tools header.
Fixes: fc92099902fb ("tools headers: Synchronize linux/bits.h with the kernel sources")
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Acked-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
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To pick up the changes in this cset:
1e7933a575ed8af4 ("uapi: Revert "bitops: avoid integer overflow in GENMASK(_ULL)"")
5b572e8a9f3dcd6e ("bits: introduce fixed-type BIT_U*()")
19408200c094858d ("bits: introduce fixed-type GENMASK_U*()")
31299a5e02112411 ("bits: add comments and newlines to #if, #else and #endif directives")
This addresses these perf build warnings:
Warning: Kernel ABI header differences:
diff -u tools/include/linux/bits.h include/linux/bits.h
Please see tools/include/uapi/README for further details.
Acked-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Cc: I Hsin Cheng <richard120310@gmail.com>
Cc: Yury Norov <yury.norov@gmail.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Yury Norov <yury.norov@gmail.com>
Link: https://lore.kernel.org/r/aEr0ZJ60EbshEy6p@x1
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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Commit 1e7933a575ed ("uapi: Revert "bitops: avoid integer overflow in GENMASK(_ULL)"")
did not take in account that the usage of BITS_PER_LONG in __GENMASK() was
changed to __BITS_PER_LONG for UAPI-safety in
commit 3c7a8e190bc5 ("uapi: introduce uapi-friendly macros for GENMASK").
BITS_PER_LONG can not be used in UAPI headers as it derives from the kernel
configuration and not from the current compiler invocation.
When building compat userspace code or a compat vDSO its value will be
incorrect.
Switch back to __BITS_PER_LONG.
Fixes: 1e7933a575ed ("uapi: Revert "bitops: avoid integer overflow in GENMASK(_ULL)"")
Cc: stable@vger.kernel.org
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Yury Norov [NVIDIA] <yury.norov@gmail.com>
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This patch reverts 'commit c32ee3d9abd2("bitops: avoid integer overflow in
GENMASK(_ULL)")'.
The code generation can be shrink by over 1KB by reverting this commit.
Originally the commit claimed that clang would emit warnings using the
implementation at that time.
The patch was applied and tested against numerous compilers, including
gcc-13, gcc-12, gcc-11 cross-compiler, clang-17, clang-18 and clang-19.
Various warning levels were set (-W=0, -W=1, -W=2) and CONFIG_WERROR
disabled to complete the compilation. The results show that no compilation
errors or warnings were generated due to the patch.
The results of code size reduction are summarized in the following table.
The code size changes for clang are all zero across different versions,
so they're not listed in the table.
For NR_CPUS=64 on x86_64.
----------------------------------------------
| | gcc-13 | gcc-12 | gcc-11 |
----------------------------------------------
| old | 22438085 | 22453915 | 22302033 |
----------------------------------------------
| new | 22436816 | 22452913 | 22300826 |
----------------------------------------------
| new - old | -1269 | -1002 | -1207 |
----------------------------------------------
For NR_CPUS=1024 on x86_64.
----------------------------------------------
| | gcc-13 | gcc-12 | gcc-11 |
----------------------------------------------
| old | 22493682 | 22509812 | 22357661 |
----------------------------------------------
| new | 22493230 | 22509487 | 22357250 |
----------------------------------------------
| new - old | -452 | -325 | -411 |
----------------------------------------------
For arm64 architecture, gcc cross-compiler was used and QEMU was
utilized to execute a VM for a CPU-heavy workload to ensure no
side effects and that functionalities remained correct. The test
even demonstrated a positive result in terms of code size reduction:
* Before: 31660668
* After: 31658724
* Difference (After - Before): -1944
An analysis of multiple functions compiled with gcc-13 on x86_64 was
performed. In summary, the patch elimates one negation in almost
every use case. However, negative effects may occur in some cases,
such as the generation of additional "mov" instruction or increased
register usage. The use of "~_UL(0) << (l)" may even result in the
allocations of "%r*" registers instead of "%e*" registers (which are
32-bit registers) because the compiler cannot assume that the higher
bits are zero.
Yury:
We limit GENMASK() usage with the const_true(l > h) condition, and
most of users just call it with constant parameters. For those, the
actual implementation of the macro doesn't matter, and since it
triggered clang warnings back then, it was reasonable to workaround
the warnings on the kernel side.
Now that some find_bit() functions call GENMASK() with runtime
parameters (although the const_true() condition holds), this ended up
hurting the generated code, as I Hsin discovered. This is especially
bad because it hurts small_const_nbits() optimization, where people are
most concerned about generated code quality. So, revert it to the
original version for good.
Signed-off-by: I Hsin Cheng <richard120310@gmail.com>
Signed-off-by: Yury Norov <yury.norov@gmail.com>
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This adds GENMASK_U128() and __GENMASK_U128() macros using __BITS_PER_U128
and __int128 data types. These macros will be used in providing support for
generating 128 bit masks.
The macros wouldn't work in all assembler flavors for reasons described
in the comments on top of declarations. Enforce it for more by adding
!__ASSEMBLY__ guard.
Cc: Yury Norov <yury.norov@gmail.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Arnd Bergmann <arnd@arndb.de>>
Cc: linux-kernel@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Yury Norov <yury.norov@gmail.com>
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Move __GENMASK and __GENMASK_ULL from include/ to include/uapi/ so that they can
be used to define masks in userspace API headers. Compared to what is already
in include/linux/bits.h, the definitions need to use the uglified versions of
UL(), ULL(), BITS_PER_LONG and BITS_PER_LONG_LONG (which did not even exist),
but otherwise expand to the same content.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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