原创 Nios中的__attribute__

这是定义main的别名为alt_main,这样当NiosII IDE的debugger的断点设置在main的时候(在Debug As...里面可以设置),
由于Free-Standing的模式下,alt_main取代了main函数(已经不存在main函数实体了),此时如果断点还设置在main的时候,上面的语法就可以就可以告诉debugger将断点设置在alt_main,从而不会出现无法在main中设置断点错误.(已经经过实际验证:建立一个freestand的项目,然后在alt_main文件中讲上面的语句注释掉,此时debug的时候就会弹出无法设置断点的错误)

weak
The weak attribute causes the declaration to be emitted as a weak symbol rather than a global. This is primarily useful in defining library functions which can be overridden in user code, though it can also be used with non-function declarations. Weak symbols are supported for ELF targets, and also for a.out targets when using the GNU assembler and linker.

 
alias ("target")
The alias attribute causes the declaration to be emitted as an alias for another symbol, which must be specified. For instance,

          void __f () { /* Do something. */; }
          void f () __attribute__ ((weak, alias ("__f")));

declares f to be a weak alias for __f. In C++, the mangled name for the target must be used.

Not all target machines support this attribute.