| Age | Commit message (Collapse) | Author |
|---|
|
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).
Add missing __attribute_const__ annotations to generic implementations of
ffs(), __ffs(), fls(), and __fls() functions. These are pure mathematical
functions that always return the same result for the same input with no
side effects, making them eligible for compiler optimization.
Build tested with x86_64 defconfig using GCC 14.2.0, which should validate
the implementations when used by ARM, ARM64, LoongArch, Microblaze,
NIOS2, and SPARC32 architectures.
Link: https://github.com/KSPP/linux/issues/364 [1]
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250804164417.1612371-2-kees@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>
|
|
The gcc compiler translates on some architectures the 64-bit
__builtin_clzll() function to a call to the libgcc function __clzdi2(),
which should take a 64-bit parameter on 32- and 64-bit platforms.
But in the current kernel code, the built-in __clzdi2() function is
defined to operate (wrongly) on 32-bit parameters if BITS_PER_LONG ==
32, thus the return values on 32-bit kernels are in the range from
[0..31] instead of the expected [0..63] range.
This patch fixes the in-kernel functions __clzdi2() and __ctzdi2() to
take a 64-bit parameter on 32-bit kernels as well, thus it makes the
functions identical for 32- and 64-bit kernels.
This bug went unnoticed since kernel 3.11 for over 10 years, and here
are some possible reasons for that:
a) Some architectures have assembly instructions to count the bits and
which are used instead of calling __clzdi2(), e.g. on x86 the bsr
instruction and on ppc cntlz is used. On such architectures the
wrong __clzdi2() implementation isn't used and as such the bug has
no effect and won't be noticed.
b) Some architectures link to libgcc.a, and the in-kernel weak
functions get replaced by the correct 64-bit variants from libgcc.a.
c) __builtin_clzll() and __clzdi2() doesn't seem to be used in many
places in the kernel, and most likely only in uncritical functions,
e.g. when printing hex values via seq_put_hex_ll(). The wrong return
value will still print the correct number, but just in a wrong
formatting (e.g. with too many leading zeroes).
d) 32-bit kernels aren't used that much any longer, so they are less
tested.
A trivial testcase to verify if the currently running 32-bit kernel is
affected by the bug is to look at the output of /proc/self/maps:
Here the kernel uses a correct implementation of __clzdi2():
root@debian:~# cat /proc/self/maps
00010000-00019000 r-xp 00000000 08:05 787324 /usr/bin/cat
00019000-0001a000 rwxp 00009000 08:05 787324 /usr/bin/cat
0001a000-0003b000 rwxp 00000000 00:00 0 [heap]
f7551000-f770d000 r-xp 00000000 08:05 794765 /usr/lib/hppa-linux-gnu/libc.so.6
...
and this kernel uses the broken implementation of __clzdi2():
root@debian:~# cat /proc/self/maps
0000000010000-0000000019000 r-xp 00000000 000000008:000000005 787324 /usr/bin/cat
0000000019000-000000001a000 rwxp 000000009000 000000008:000000005 787324 /usr/bin/cat
000000001a000-000000003b000 rwxp 00000000 00:00 0 [heap]
00000000f73d1000-00000000f758d000 r-xp 00000000 000000008:000000005 794765 /usr/lib/hppa-linux-gnu/libc.so.6
...
Signed-off-by: Helge Deller <deller@gmx.de>
Fixes: 4df87bb7b6a22 ("lib: add weak clz/ctz functions")
Cc: Chanho Min <chanho.min@lge.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: stable@vger.kernel.org # v3.11+
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
|
|
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 <tglx@linutronix.de>
Reviewed-by: Enrico Weigelt <info@metux.net>
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Allison Randal <allison@lohutok.net>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190604081206.933168790@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
|
|
Add prototype declarations of functions in lib/clz_ctz.c. These
functions are required by GCC builtins and hence can not be removed
despite of their unreferenced appearance in kernel source.
This eliminates the following warning in lib/clz_ctz.c:
lib/clz_ctz.c:16:12: warning: no previous prototype for `__ctzsi2' [-Wmissing-prototypes]
lib/clz_ctz.c:22:12: warning: no previous prototype for `__clzsi2' [-Wmissing-prototypes]
lib/clz_ctz.c:44:12: warning: no previous prototype for `__clzdi2' [-Wmissing-prototypes]
lib/clz_ctz.c:50:12: warning: no previous prototype for `__ctzdi2' [-Wmissing-prototypes]
Signed-off-by: Rashika Kheria <rashika.kheria@gmail.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Acked-by: Chanho Min <chanho.min@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
|
|
Some architectures need __c[lt]z[sd]i2() for __builtin_c[lt]z[ll] and
that causes a build failure. They can be implemented using the
fls()/__ffs() and overridden by linking arch-specific versions may not
be implemented yet.
This is required by "lib: add lz4 compressor module".
Reference: https://lkml.org/lkml/2013/4/18/603
Signed-off-by: Chanho Min <chanho.min@lge.com>
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: "Darrick J. Wong" <djwong@us.ibm.com>
Cc: Bob Pearson <rpearson@systemfabricworks.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Herbert Xu <herbert@gondor.hengli.com.au>
Cc: Yann Collet <yann.collet.73@gmail.com>
Cc: Kyungsik Lee <kyungsik.lee@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
|
