kernel/linux.git/arch/arc/include/asm/bitops.h, branch v5.10.257

arc: Fix fls() const-foldability via builtin_clzl()

2025-12-06T21:08:09+00:00

[ Upstream commit a3fecb9160482367365cc384c59dd220b162b066 ] While tracking down a problem where constant expressions used by BUILD_BUG_ON() suddenly stopped working[1], we found that an added static initializer was convincing the compiler that it couldn't track the state of the prior statically initialized value. Tracing this down found that ffs() was used in the initializer macro, but since it wasn't marked with __attribute__const__, the compiler had to assume the function might change variable states as a side-effect (which is not true for ffs(), which provides deterministic math results). For arc architecture with CONFIG_ISA_ARCV2=y, the __fls() function uses __builtin_arc_fls() which lacks GCC's const attribute, preventing compile-time constant folding, and KUnit testing of ffs/fls fails on arc[3]. A patch[2] to GCC to solve this has been sent. Add a fix for this by handling compile-time constants with the standard __builtin_clzl() builtin (which has const attribute) while preserving the optimized arc-specific builtin for runtime cases. This has the added benefit of skipping runtime calculation of compile-time constant values. Even with the GCC bug fixed (which is about "attribute const") this is a good change to avoid needless runtime costs, and should be done regardless of the state of GCC's bug. Build tested ARCH=arc allyesconfig with GCC arc-linux 15.2.0. Link: https://github.com/KSPP/linux/issues/364 [1] Link: https://gcc.gnu.org/pipermail/gcc-patches/2025-August/693273.html Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-kbuild-all/202508031025.doWxtzzc-lkp@intel.com/ [3] Signed-off-by: Kees Cook Acked-by: Vineet Gupta Signed-off-by: Yury Norov (NVIDIA) Signed-off-by: Sasha Levin

ARC: bitops: Remove unecessary operation and value

2020-11-18T04:10:21+00:00

The 1-bit shift rotation to the left on x variable located on 4 last if statement can be removed because the computed value is will not be used afront. Signed-off-by: Gustavo Pimentel Signed-off-by: Vineet Gupta

ARC: [plat-eznps]: Drop support for EZChip NPS platform

2020-10-06T04:02:29+00:00

NPS customers are no longer doing active development, as evident from rand config build failures reported in recent times, so drop support for NPS platform. Tested-by: kernel test robot Signed-off-by: Vineet Gupta

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500

2019-06-19T15:09:55+00:00

Based on 2 normalized pattern(s): this program is free software you can redistribute it and or modify it under the terms of the gnu general public license version 2 as published by the free software foundation this program is free software you can redistribute it and or modify it under the terms of the gnu general public license version 2 as published by the free software foundation # extracted by the scancode license scanner the SPDX license identifier GPL-2.0-only has been chosen to replace the boilerplate/reference in 4122 file(s). Signed-off-by: Thomas Gleixner Reviewed-by: Enrico Weigelt Reviewed-by: Kate Stewart Reviewed-by: Allison Randal Cc: linux-spdx@vger.kernel.org Link: https://lkml.kernel.org/r/20190604081206.933168790@linutronix.de Signed-off-by: Greg Kroah-Hartman

ARC: fix __ffs return value to avoid build warnings

2019-01-17T22:38:00+00:00

| CC mm/nobootmem.o |In file included from ./include/asm-generic/bug.h:18:0, | from ./arch/arc/include/asm/bug.h:32, | from ./include/linux/bug.h:5, | from ./include/linux/mmdebug.h:5, | from ./include/linux/gfp.h:5, | from ./include/linux/slab.h:15, | from mm/nobootmem.c:14: |mm/nobootmem.c: In function '__free_pages_memory': |./include/linux/kernel.h:845:29: warning: comparison of distinct pointer types lacks a cast | (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1))) | ^ |./include/linux/kernel.h:859:4: note: in expansion of macro '__typecheck' | (__typecheck(x, y) && __no_side_effects(x, y)) | ^~~~~~~~~~~ |./include/linux/kernel.h:869:24: note: in expansion of macro '__safe_cmp' | __builtin_choose_expr(__safe_cmp(x, y), \ | ^~~~~~~~~~ |./include/linux/kernel.h:878:19: note: in expansion of macro '__careful_cmp' | #define min(x, y) __careful_cmp(x, y, <) | ^~~~~~~~~~~~~ |mm/nobootmem.c:104:11: note: in expansion of macro 'min' | order = min(MAX_ORDER - 1UL, __ffs(start)); Change __ffs return value from 'int' to 'unsigned long' as it is done in other implementations (like asm-generic, x86, etc...) to avoid build-time warnings in places where type is strictly checked. As __ffs may return values in [0-31] interval changing return type to unsigned is valid. Signed-off-by: Eugeniy Paltsev Signed-off-by: Vineet Gupta

fls: change parameter to unsigned int

2019-01-04T21:13:46+00:00

When testing in userspace, UBSAN pointed out that shifting into the sign bit is undefined behaviour. It doesn't really make sense to ask for the highest set bit of a negative value, so just turn the argument type into an unsigned int. Some architectures (eg ppc) already had it declared as an unsigned int, so I don't expect too many problems. Link: http://lkml.kernel.org/r/20181105221117.31828-1-willy@infradead.org Signed-off-by: Matthew Wilcox Acked-by: Thomas Gleixner Acked-by: Geert Uytterhoeven Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ARC: [plat-eznps] Use dedicated atomic/bitops/cmpxchg

2016-05-09T04:02:33+00:00

We need our own implementaions since we lack LLSC support. Our extended ISA provided with optimized solution for all 32bit operations we see in these three headers. Signed-off-by: Noam Camus

ARC: bitops: Remove non relevant comments

2016-03-11T09:29:54+00:00

commit 80f420842ff42 removed the ARC bitops microoptimization but failed to prune the comments to same effect Fixes: 80f420842ff42 ("ARC: Make ARC bitops "safer" (add anti-optimization)") Signed-off-by: Vineet Gupta

ARC: Make ARC bitops "safer" (add anti-optimization)

2015-07-09T12:06:32+00:00

ARCompact/ARCv2 ISA provide that any instructions which deals with bitpos/count operand ASL, LSL, BSET, BCLR, BMSK .... will only consider lower 5 bits. i.e. auto-clamp the pos to 0-31. ARC Linux bitops exploited this fact by NOT explicitly masking out upper bits for @nr operand in general, saving a bunch of AND/BMSK instructions in generated code around bitops. While this micro-optimization has worked well over years it is NOT safe as shifting a number with a value, greater than native size is "undefined" per "C" spec. So as it turns outm EZChip ran into this eventually, in their massive muti-core SMP build with 64 cpus. There was a test_bit() inside a loop from 63 to 0 and gcc was weirdly optimizing away the first iteration (so it was really adhering to standard by implementing undefined behaviour vs. removing all the iterations which were phony i.e. (1 << [63..32]) | for i = 63 to 0 | X = ( 1 << i ) | if X == 0 | continue So fix the code to do the explicit masking at the expense of generating additional instructions. Fortunately, this can be mitigated to a large extent as gcc has SHIFT_COUNT_TRUNCATED which allows combiner to fold masking into shift operation itself. It is currently not enabled in ARC gcc backend, but could be done after a bit of testing. Fixes STAR 9000866918 ("unsafe "undefined behavior" code in kernel") Reported-by: Noam Camus Cc: Signed-off-by: Vineet Gupta

ARC: Reduce bitops lines of code using macros

2015-06-25T00:30:18+00:00

No semantical changes ! Acked-by: Peter Zijlstra (Intel) Signed-off-by: Vineet Gupta