varargs

[Ian Lance Taylor]

Constantine Kousoulos <wuwei@freemail.gr> writes:

> I have a printf() function written in C using va_start, va_arg,
> etc. It works fine on i386. Lately, i needed it on my amd64
> machine. However, although it builds, it does not work.
> 
> After reading the x86_64 ABI, i found out that on amd64 each
> function's args are moved to specific registers and not to the stack
> (like on i386).
> 
> Do i need to do something extra to use varargs functions on x86_64?

No.  Doing a #include of <stdarg.h> should suffice.

Note that on x86_64, unlike i386, int and long have different sizes.
That means that varargs functions have more chances to make mistakes.
If the caller passes a long, you must use va_arg(long), not
va_arg(int).

Ian