Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
Merge branch 'arm64/for-next/read-once'
Need the arm64 READ_ONCE() rework, otherwise clang context analysis can't see through it.
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
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arch/arm64/include/asm/rwonce.h
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arch/arm64/include/asm/rwonce.h
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ARM64_HAS_LDAPR)
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/*
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* Replace this with typeof_unqual() when minimum compiler versions are
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* increased to GCC 14 and Clang 19. For the time being, we need this
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* workaround, which relies on function return values dropping qualifiers.
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*/
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#define __rwonce_typeof_unqual(x) typeof(({ \
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__diag_push() \
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__diag_ignore_all("-Wignored-qualifiers", "") \
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((typeof(x)(*)(void))0)(); \
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__diag_pop() }))
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/*
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* When building with LTO, there is an increased risk of the compiler
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* converting an address dependency headed by a READ_ONCE() invocation
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* into a control dependency and consequently allowing for harmful
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*/
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#define __READ_ONCE(x) \
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({ \
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typeof(&(x)) __x = &(x); \
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int atomic = 1; \
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union { __unqual_scalar_typeof(*__x) __val; char __c[1]; } __u; \
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auto __x = &(x); \
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auto __ret = (__rwonce_typeof_unqual(*__x) *)__x; \
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/* Hides alias reassignment from Clang's -Wthread-safety. */ \
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auto __retp = &__ret; \
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union { typeof(*__ret) __val; char __c[1]; } __u; \
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*__retp = &__u.__val; \
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switch (sizeof(x)) { \
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case 1: \
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asm volatile(__LOAD_RCPC(b, %w0, %1) \
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: "Q" (*__x) : "memory"); \
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break; \
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default: \
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atomic = 0; \
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__u.__val = *(volatile typeof(*__x) *)__x; \
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} \
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atomic ? (typeof(*__x))__u.__val : (*(volatile typeof(*__x) *)__x);\
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*__ret; \
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})
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#endif /* !BUILD_VDSO */