do ... while(0) in macros

[CARERI/SED]

There are many macros in RTEMS written like the following code:

  do { \
    unsigned32 _stack; \
    \
    if ( (_isr) ) (_the_context)->eflags = CPU_EFLAGS_INTERRUPTS_OFF; \
    else          (_the_context)->eflags = CPU_EFLAGS_INTERRUPTS_ON; \
    \
    _stack = ((unsigned32)(_stack_base)) + (_size) - 4; \
    \
    *((proc_ptr *)(_stack)) = (_entry_point); \
    (_the_context)->ebp     = (void *) _stack; \
    (_the_context)->esp     = (void *) _stack; \
  } while (0)

Could anybody explain the purpose of the "do ... while(0)" ?

Thanks in advance,

Guo
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