Use va_copy() where available. This should fix a segfault in vsnprintf()

on AMD 64 Linux.
(This has been sitting in my checkout for ages and hasn't obviously caused
any trouble -- I think I was waiting to get round to trying it with VC6, which
I haven't yet. There are some notes in comments on further tweaks that could
be made.)

git-svn-id: svn://svn.tartarus.org/sgt/putty@7035 cda61777-01e9-0310-a592-d414129be87e

diff --git a/misc.c b/misc.c
index 09506de..3a27572 100644 (file)
--- a/misc.c
+++ b/misc.c
@@ -180,20 +180,11 @@ char *dupcat(const char *s1, ...)
  * Do an sprintf(), but into a custom-allocated buffer.
  * 
  * Currently I'm doing this via vsnprintf. This has worked so far,
- * but it's not good, because:
- * 
- *  - vsnprintf is not available on all platforms. There's an ifdef
- *    to use `_vsnprintf', which seems to be the local name for it
- *    on Windows. Other platforms may lack it completely, in which
- *    case it'll be time to rewrite this function in a totally
- *    different way.
- * 
- *  - technically you can't reuse a va_list like this: it is left
- *    unspecified whether advancing a va_list pointer modifies its
- *    value or something it points to, so on some platforms calling
- *    vsnprintf twice on the same va_list might fail hideously. It
- *    would be better to use the `va_copy' macro mandated by C99,
- *    but that too is not yet ubiquitous.
+ * but it's not good, because vsnprintf is not available on all
+ * platforms. There's an ifdef to use `_vsnprintf', which seems
+ * to be the local name for it on Windows. Other platforms may
+ * lack it completely, in which case it'll be time to rewrite
+ * this function in a totally different way.
  * 
  * The only `properly' portable solution I can think of is to
  * implement my own format string scanner, which figures out an
@@ -241,7 +232,24 @@ char *dupvprintf(const char *fmt, va_list ap)
 #ifdef _WINDOWS
 #define vsnprintf _vsnprintf
 #endif
+#ifdef va_copy
+       /* Use the `va_copy' macro mandated by C99, if present.
+        * XXX some environments may have this as __va_copy() */
+       va_list aq;
+       va_copy(aq, ap);
+       len = vsnprintf(buf, size, fmt, aq);
+       va_end(aq);
+#else
+       /* Ugh. No va_copy macro, so do something nasty.
+        * Technically, you can't reuse a va_list like this: it is left
+        * unspecified whether advancing a va_list pointer modifies its
+        * value or something it points to, so on some platforms calling
+        * vsnprintf twice on the same va_list might fail hideously
+        * (indeed, it has been observed to).
+        * XXX the autoconf manual suggests that using memcpy() will give
+        *     "maximum portability". */
        len = vsnprintf(buf, size, fmt, ap);
+#endif
        if (len >= 0 && len < size) {
            /* This is the C99-specified criterion for snprintf to have
             * been completely successful. */