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6ec4476ac8
I realize that we fairly recently raised it to 4.8, but the fact is, 4.9
is a much better minimum version to target.
We have a number of workarounds for actual bugs in pre-4.9 gcc versions
(including things like internal compiler errors on ARM), but we also
have some syntactic workarounds for lacking features.
In particular, raising the minimum to 4.9 means that we can now just
assume _Generic() exists, which is likely the much better replacement
for a lot of very convoluted built-time magic with conditionals on
sizeof and/or __builtin_choose_expr() with same_type() etc.
Using _Generic also means that you will need to have a very recent
version of 'sparse', but thats easy to build yourself, and much less of
a hassle than some old gcc version can be.
The latest (in a long string) of reasons for minimum compiler version
upgrades was commit 5435f73d5c ("efi/x86: Fix build with gcc 4").
Ard points out that RHEL 7 uses gcc-4.8, but the people who stay back on
old RHEL versions persumably also don't build their own kernels anyway.
And maybe they should cross-built or just have a little side affair with
a newer compiler?
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
47 lines
1.4 KiB
C
47 lines
1.4 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef __LINUX_BITS_H
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#define __LINUX_BITS_H
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#include <linux/const.h>
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#include <vdso/bits.h>
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#include <asm/bitsperlong.h>
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#define BIT_ULL(nr) (ULL(1) << (nr))
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#define BIT_MASK(nr) (UL(1) << ((nr) % BITS_PER_LONG))
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#define BIT_WORD(nr) ((nr) / BITS_PER_LONG)
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#define BIT_ULL_MASK(nr) (ULL(1) << ((nr) % BITS_PER_LONG_LONG))
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#define BIT_ULL_WORD(nr) ((nr) / BITS_PER_LONG_LONG)
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#define BITS_PER_BYTE 8
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/*
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* Create a contiguous bitmask starting at bit position @l and ending at
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* position @h. For example
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* GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000.
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*/
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#if !defined(__ASSEMBLY__)
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#include <linux/build_bug.h>
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#define GENMASK_INPUT_CHECK(h, l) \
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(BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
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__builtin_constant_p((l) > (h)), (l) > (h), 0)))
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#else
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/*
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* BUILD_BUG_ON_ZERO is not available in h files included from asm files,
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* disable the input check if that is the case.
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*/
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#define GENMASK_INPUT_CHECK(h, l) 0
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#endif
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#define __GENMASK(h, l) \
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(((~UL(0)) - (UL(1) << (l)) + 1) & \
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(~UL(0) >> (BITS_PER_LONG - 1 - (h))))
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#define GENMASK(h, l) \
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(GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
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#define __GENMASK_ULL(h, l) \
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(((~ULL(0)) - (ULL(1) << (l)) + 1) & \
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(~ULL(0) >> (BITS_PER_LONG_LONG - 1 - (h))))
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#define GENMASK_ULL(h, l) \
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(GENMASK_INPUT_CHECK(h, l) + __GENMASK_ULL(h, l))
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#endif /* __LINUX_BITS_H */
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