OSDev.org

Posted: **Wed Feb 02, 2011 10:50 am**

Hi
I was coding the printk routine for which i needed the varargs. As mentioned in one of the printing tutorials on this website it uses gcc's in built version.

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#define va_start(v,l) __builtin_va_start(v,l)
#define va_arg(v,l)   __builtin_va_arg(v,l)
#define va_end(v)     __builtin_va_end(v)
#define va_copy(d,s)  __builtin_va_copy(d,s)
typedef __builtin_va_list va_list

The problem is as soon i insert this code i get a weird error

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error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘extern’

Any thoughts on how to get it working. I tried one of the other implementations which is here,

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typedef char* va_list;

#define _INTSIZEOF(n)   ( (sizeof(n) + sizeof(int) - 1) & ~(sizeof(int) - 1) )

#define va_start(ap,v)  ( ap = (va_list)&v + _INTSIZEOF(v) )

#define va_arg(argp,type) (*(type *)(((argp) +=_INTSIZEOF(type))-_INTSIZEOF(type)))

#define va_end(x) (x=(void*)0)

but this implementation isn't working for me at least with gcc.
I've gcc version 4.4.1 OpenSuse11.2 for developing the kernel.

Posted: **Wed Feb 02, 2011 12:34 pm**

pranjas wrote:
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typedef __builtin_va_list va_list
The problem is as soon i insert this code i get a weird error
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error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘extern’
Any thoughts on how to get it working. I tried one of the other implementations which is here,

I'm not sure if this might be a problem, but shouldn't the aforementioned line of code end with a ';'? Maybe this will fix it? Unless it was just a mistake in typing it into osdev's editor?

Regards,
~Kris

Posted: **Wed Feb 02, 2011 1:22 pm**

i think i understand your mistake.

If you use a compiler directive (one that starts with '#'), then the line does not need to end with ';', so:

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#define HI 0x555

is valid syntax. However, 'typedef' is technically not a compiler directive. So this:

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typedef char*  va_list

is invalid. You must add a ';' at the end, like this:

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typedef char * va_list;

I had these kinds of problems all the time. Hope I helped

Posted: **Wed Feb 02, 2011 9:20 pm**

!... yeah there's no ; after the typedef.

thanks... i guess worrying too much about bigger problems i'm facing couldn't notice this small mistake...
really embarassed

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