Re: [PATCH] Add compat/vsnprintf.c for systems that returns -1 on maxsize reached

From: Johannes Sixt <j.sixt@viscovery.net>
Date: Mar 4, 2008, 16:19 UTC
Message-ID: <47CD7686.9040501@viscovery.net>
In-Reply-To: <20080304140930.GA23335@pvv.org>

Finn Arne Gangstad schrieb:

Show 14 quoted lines

> On Tue, Mar 04, 2008 at 02:59:28PM +0100, Michal Rokos wrote:
> 
>> +	while ( ret == -1 )
>> +	{
>> +		maxsize = (maxsize*3)/2;
>> +		s = realloc(s, maxsize);
>> +		if (! s) return -1;
>> +		ret = vsnprintf(s, maxsize, format, ap);  /* <--- UNSAFE! */
>> +	}
> 
> This is not generally safe, you cannot call vsnprintf multiple times
> with the same ap on all architectures. You need va_copy (or __va_copy,
> or VA_COPY, differs a bit between different architectures, especially
> one the ones with a broken vsnprintf I guess..)

True. But...

This replacement of vsnprintf will not be needed on all architectures, but only on some. And on these we can test in advance whether we can get away without va_copy (et.al.). A note next to the configuration setting about this would be in order, I think.

Furthermore, on systems where vsnprintf is broken in this way, va_copy is likely not available.

-- Hannes