GCC 位属性 [英] GCC Bitwise Attribute

问题描述

GCC 的 __attribute__(bitwise) 是什么意思?GCC-4.6 的信息页面中没有提到该属性.我在项目 Open-ISCSI 的源文件 open-iscsi-2.0.871/include/iscsi_proto.h 中偶然发现了它

What does GCC's __attribute__(bitwise) mean? The attribute isn't mentioned in the info pages of GCC-4.6. I stumbled upon it in the file open-iscsi-2.0.871/include/iscsi_proto.h in source the project Open-ISCSI where it is used as

...
/*
 * If running svn modules we may need to define these.
 * This should not go upstream since this is already properly defined there
 */
#ifdef __CHECKER__
#define __bitwise__ __attribute__((bitwise))
#else
#define __bitwise__
#endif
#ifdef __CHECK_ENDIAN__
#define __bitwise __bitwise__
#else
#define __bitwise
#endif

/*! initiator tags; opaque for target */
typedef uint32_t __bitwise__ itt_t;
/*! below makes sense only for initiator that created this tag */
#define build_itt(itt, age) ((__force itt_t)
    ((itt) | ((age) << ISCSI_AGE_SHIFT)))
#define get_itt(itt) ((__force uint32_t)(itt_t)(itt) & ISCSI_ITT_MASK)
#define RESERVED_ITT ((__force itt_t)0xffffffff)
...

我怀疑涉及字节顺序的事情，但我无法理解上面给出的片段.

I'm suspecting something involving byte-order but I can't make any sense of the snippet given above.

推荐答案

这显然不是 GCC 使用的，而是 Sparse，Linux 内核使用的 C 语义解析器.它记录在 文档/dev-tools/sparse.txt.

This is apparently not used by GCC but by Sparse, a semantic parser for C used by the Linux kernel. It is documented in Documentation/dev-tools/sparse.txt.

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