varargs

varargs

[Phil Prentice]

Hi

  We are currently porting software using the gnu compiler (3.3.3).  Its 
working very well so far, but we have a problem over varargs.

  There are dozens of files which use varargs (not stdarg).  In time we will 
move these files over to use stdarg, however we have the added problem of 
there having to be at least one parameter being declared for stdarg to 
compile and work.

  1)  Is there anyway that we can cheat here  or do we have to go through all 
the function calls and add a dummy parameter etc to enable us to use 
stdarg's??  Many of these functions accept 0 or more tag parameters. How do 
we cope with no parameters?

   2) Same question really, but a considerably amount of software exists  
which interfaces to our varargs software which would be nia on impossible to 
change.  Again in this case are we stuck to having to use an older version of 
the compiler which supports varargs or again can we cheat somehow?

  3)  What is the latest version of the compiler that still supports varargs?

  It would be nice to use stdarg but without the worry of changing the 
calling software?  Is there any way around the problem of zero parameters?


Thanks again for all your help

  Phil

Re: varargs

[llewelly]

Phil Prentice <philp.cheer@btinternet.com> writes:

> Hi
> 
>   We are currently porting software using the gnu compiler (3.3.3).  Its 
> working very well so far, but we have a problem over varargs.

Sorry, but I think gcc support for varargs and other pre-C89
    constructs is a thing of the past. gcc 3.2 was the last to
    support -traditional, and I can't find the docs for when varargs
    support was dropped. I suppose you could try 3.2.3 as an interm
    solution.

> 
>   There are dozens of files which use varargs (not stdarg).  In time we will 
> move these files over to use stdarg, however we have the added problem of 
> there having to be at least one parameter being declared for stdarg to 
> compile and work.
> 
>   1)  Is there anyway that we can cheat here  or do we have to go through all 
> the function calls and add a dummy parameter etc to enable us to use 
> stdarg's??  Many of these functions accept 0 or more tag parameters. How do 
> we cope with no parameters?
> 
>    2) Same question really, but a considerably amount of software exists  
> which interfaces to our varargs software which would be nia on impossible to 
> change.  Again in this case are we stuck to having to use an older version of 
> the compiler which supports varargs or again can we cheat somehow?
[snip]

I can't think of any off the top of my head, but I would be tempted to
    experiment with some well-thought-out macro-hackery.

Re: 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

varargs

[Constantine Kousoulos]

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?

Thanks,
Constantine

PS I'm using gcc-4.1.3.