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85 lines
2.3 KiB
C
85 lines
2.3 KiB
C
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/*
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* C23 introduces an attribute syntax `[[<attribute>]]`. Prior to that
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* other non-standard syntaxes such as `__attribute__((<attribute>))`
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* and `__declspec(<attribute>)` have been supported by some compiler
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* versions.
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*
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* See also:
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* https://en.cppreference.com/w/c/language/attributes
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*
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* There is no portable way to use C23 attributes in older C standards
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* so in order to use these portably, some macro name needs to be
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* defined for each attribute that either maps to the older supported
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* syntax, or ignores the attribute as appropriate.
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*
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* The Linux kernel defines certain attributes as macros, such as
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* `fallthrough`. When adding attributes it seems reasonable to follow
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* the Linux conventions in lack of any official standard. However, it
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* is not the intention that this file should mirror the Linux
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* attributes 1 to 1.
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*
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* See also:
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* https://github.com/torvalds/linux/blob/master/include/linux/compiler_attributes.h
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*
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* There is a risk that exposed attribute names may lead to name
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* conflicts. A conflicting name can be undefined and if necessary used
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* using `pattribute(<attribute>)`. All attributes can be hidden by
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* defining `PORTABLE_EXPOSE_ATTRIBUTES=0` in which case
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* `pattribute(<attribute>)` can still be used and then if a specific
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* attribute name still needs to be exposed, it can be defined manually
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* like `#define fallthrough pattribute(fallthrough)`.
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*/
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#ifndef PATTRIBUTES_H
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#define PATTRIBUTES_H
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#ifdef __cplusplus
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extern "C" {
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#endif
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#ifndef PORTABLE_EXPOSE_ATTRIBUTES
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#define PORTABLE_EXPOSE_ATTRIBUTES 1
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#endif
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#ifdef __has_c_attribute
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# define PORTABLE_HAS_C_ATTRIBUTE(x) __has_c_attribute(x)
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#else
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# define PORTABLE_HAS_C_ATTRIBUTE(x) 0
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#endif
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#ifdef __has_attribute
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# define PORTABLE_HAS_ATTRIBUTE(x) __has_attribute(x)
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#else
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# define PORTABLE_HAS_ATTRIBUTE(x) 0
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#endif
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/* https://en.cppreference.com/w/c/language/attributes/fallthrough */
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#if PORTABLE_HAS_C_ATTRIBUTE(__fallthrough__)
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# define pattribute_fallthrough [[__fallthrough__]]
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#elif PORTABLE_HAS_ATTRIBUTE(__fallthrough__)
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# define pattribute_fallthrough __attribute__((__fallthrough__))
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#else
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# define pattribute_fallthrough ((void)0)
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#endif
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#define pattribute(x) pattribute_##x
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#if PORTABLE_EXPOSE_ATTRIBUTES
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#ifndef fallthrough
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# define fallthrough pattribute(fallthrough)
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#endif
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#endif
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#ifdef __cplusplus
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}
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#endif
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#endif /* PATTRIBUTES_H */
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