Re: va_copy is not available on all systems.

From: Michael Poole <mdpoole@troilus.org>
Date: Aug 20, 2007, 13:39 UTC
Message-ID: <87y7g6wcix.fsf@graviton.dyn.troilus.org>
In-Reply-To: <46C99448.2AB33DFF@eudaptics.com>

Johannes Sixt writes:

Show 10 quoted lines

> This is just too ugly to be included...
>
> die_nicely() uses the variable argument list twice. The recent fix for
> this in 7e5dcea8311 uses va_copy. However, on older systems this function
> is not available. This fix assumes that those systems that do have
> the function actually implement it as macro, and we use it to remove
> the entire nicely() functionality.
>
> Since va_copy() must be provided by the compiler, we don't have a
> reasonable chance to provide a working definition in git_compat_util.h.

Some older (pre-C99) versions of gcc name it __va_copy() instead. Is there any guarantee that va_copy() will be a macro on systems that provide it? If neither va_copy() nor __va_copy() are available, memcpy(&(DEST), &(SRC), sizeof(DEST)) should work for any va_list type. It's what I use on one project:

#ifdef HAVE_VA_COPY #define VA_COPY(DEST, SRC) va_copy(DEST, SRC) #elif HAVE___VA_COPY #define VA_COPY(DEST, SRC) __va_copy(DEST, SRC) #else #define VA_COPY(DEST, SRC) memcpy(&(DEST), &(SRC), sizeof(DEST)) #endif

with appropriate autoconf tests, basically two copies of this:

dnl How to copy one va_list to another?
AC_CACHE_CHECK([for va_copy], ac_cv_c_va_copy, [AC_LINK_IFELSE(
  [AC_LANG_PROGRAM([#include <stdarg.h>], [va_list ap1, ap2; va_copy(ap1, ap2);])],
  [ac_cv_c_va_copy="yes"],
  [ac_cv_c_va_copy="no"]
)])
if test "$ac_cv_c_va_copy" = "yes" ; then
  AC_DEFINE(HAVE_VA_COPY, 1, [Define if we have va_copy])
fi

I'm not sure how to translate the tests to git's coding style most easily.

Michael Poole