c - 什么是 "__maybe_unused"？

Question

在查看 Linux 内核时，我注意到了这一行:

static void *malloc(size_t size) __maybe_unused;

在 Linux v3.2/arch/frv/kernel/gdb_stub.c 中。我以前从未见过 __maybe_unused 被使用过。它是特定于 Linux 内核的吗？或者它是在 C 规范中定义的吗？它到底有什么作用？

Answer 1

在 include/linux/compiler-gcc.h 中有 __maybe_unused 宏的定义:

#define __maybe_unused  __attribute__((unused))

在 gcc 手册中，您有函数的 unused 属性的文档:

unused "This attribute, attached to a function, means that the function is meant to be possibly unused. GCC will not produce a warning for this function."

http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html

对于变量:

unused "This attribute, attached to a variable, means that the variable is meant to be possibly unused. GCC will not produce a warning for this variable."

http://gcc.gnu.org/onlinedocs/gcc/Variable-Attributes.html