asm volatile(...);
__asm__ __volatile__(...);
I see both are used; why create some duplicate stuff?
asm volatile(…); __asm__ __volatile__(…); I see both are used; why create some duplicate stuff?
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asm volatile(...);
__asm__ __volatile__(...);
I see both are used; why create some duplicate stuff?
The C standard reserves ‘asm’ for use by users for any purpose. Therefore, GCC provides the
__asm__notation to avoid running into the user’s name space (because identifiers starting with double underscore are reserved for the implementation).The notation with the double underscore is ungainly, so GCC provides the pleasanter interface without the double underscores. But if you turn on a standard-compliant compilation mode (such as
-std=c99), theasmoption is turned off. By writing with the double underscore notation, it is always available.So,
asmis pleasanter to read, but__asm__is compliant with the C standard.