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

From: Michal Rokos <michal.rokos@nextsoft.cz>
Date: Mar 5, 2008, 08:37 UTC
Message-ID: <200803050937.40345.michal.rokos@nextsoft.cz>
In-Reply-To: <47CD78C9.80003@viscovery.net>

Hello,

On Tuesday 04 March 2008 17:28:57 Johannes Sixt wrote:

Show 5 quoted lines

> Michal Rokos schrieb:
> > If anybody could think of some better define than BROKEN_VSNPRINTF, I'm
> > all ears.
>
> CLUELESS_OVERFLOWN_VSNPRINTF?

Heh. My first one was VSNPRINTF_RETURNS_MINUS_1...

Show 9 quoted lines

> Because we have the same issue on Windows where vsnprintf returns -1 on
> overflow.
>
> But there is also another complication: The size parameter of the system's
> vsnprintf must not count the trailing NUL, i.e. the buffer must actually
> have space for one extra byte, whereas the POSIX version must count NUL.
> Can you check whether your vsnprintf has this flaw, too? If it doesn't, we
> would need another configuration variable so that we can distinguish these
> two kinds of brokenness.

I did my homework and prepared this:

#include "stdio.h" #include "stdarg.h"

int test_vsnprintf(char *str, size_t maxsize, const char *format, ...)
{
  int ret;
  va_list ap;

  va_start(ap, format);
  ret = vsnprintf(str, maxsize, format, ap);
  va_end(ap);

  return ret;
}

int main(void)
{
  char buf[10];
  int ret;

  ret = test_vsnprintf(buf, 1, "%s", "12345");
  printf("case1: %d\n", ret);

  ret = test_vsnprintf(buf, 5, "%s", "12345");
  printf("case2: %d\n", ret);

  ret = test_vsnprintf(buf, 6, "%s", "12345");
  printf("case3: %d\n", ret);

  ret = test_vsnprintf(buf, 10, "%s", "12345");
  printf("case4: %d\n", ret);

  return 0;
}

which returns: Linux 2.6.25-rc3-mr i686 case1: 5 case2: 5 case3: 5 case4: 5

HP-UX B.11.11 9000/800 case1: -1 case2: -1 case3: 5 case4: 5

HP-UX B.11.23 ia64 case1: -1 case2: -1 case3: 5 case4: 5

So HPUX impl is the same as a Windows one. So we can share the replacement. Please note that there's no va_copy() on HPUX.

I think that Tru64 has the same issue, but I have no HW to test it on now.

Could somebody else try to run testcase above on some other OSes?

Thanks

Michal