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Recently discovered this entry while checking kallsyms on ARM64: ffff800083e509c0 D _shared_alloc_tag If ARCH_NEEDS_WEAK_PER_CPU is not defined(it is only defined for s390 and alpha architectures), there's no need to statically define the percpu variable _shared_alloc_tag. Therefore, we need to implement isolation for this purpose. When building the core kernel code for s390 or alpha architectures, ARCH_NEEDS_WEAK_PER_CPU remains undefined (as it is gated by #if defined(MODULE)). However, when building modules for these architectures, the macro is explicitly defined. Therefore, we remove all instances of ARCH_NEEDS_WEAK_PER_CPU from the code and introduced CONFIG_ARCH_MODULE_NEEDS_WEAK_PER_CPU to replace the relevant logic. We can now conditionally define the perpcu variable _shared_alloc_tag based on CONFIG_ARCH_MODULE_NEEDS_WEAK_PER_CPU. This allows architectures (such as s390/alpha) that require weak definitions for percpu variables in modules to include the definition, while others can omit it via compile-time exclusion. Link: https://lkml.kernel.org/r/20250618015809.1235761-1-hao.ge@linux.dev Signed-off-by: Hao Ge <gehao@kylinos.cn> Suggested-by: Suren Baghdasaryan <surenb@google.com> Acked-by: Alexander Gordeev <agordeev@linux.ibm.com> [s390] Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org> Cc: Chistoph Lameter <cl@linux.com> Cc: Christian Borntraeger <borntraeger@linux.ibm.com> Cc: David Hildenbrand <david@redhat.com> Cc: Dennis Zhou <dennis@kernel.org> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Kent Overstreet <kent.overstreet@linux.dev> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Matt Turner <mattst88@gmail.com> Cc: Richard Henderson <richard.henderson@linaro.org> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
19 lines
532 B
C
19 lines
532 B
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef __ALPHA_PERCPU_H
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#define __ALPHA_PERCPU_H
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/*
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* To calculate addresses of locally defined variables, GCC uses
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* 32-bit displacement from the GP. Which doesn't work for per cpu
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* variables in modules, as an offset to the kernel per cpu area is
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* way above 4G.
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*
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* Always use weak definitions for percpu variables in modules.
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* Therefore, we have enabled CONFIG_ARCH_MODULE_NEEDS_WEAK_PER_CPU
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* in the Kconfig.
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*/
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#include <asm-generic/percpu.h>
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#endif /* __ALPHA_PERCPU_H */
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