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compat/snprintf: don't look at va_list twice

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If you define SNPRINTF_RETURNS_BOGUS, we use a special
git_vsnprintf wrapper assumes that vsnprintf returns "-1"
instead of the number of characters that you would need to
store the result.

To do this, it invokes vsnprintf multiple times, growing a
heap buffer until we have enough space to hold the result.
However, this means we evaluate the va_list parameter
multiple times, which is generally a bad thing (it may be
modified by calls to vsnprintf, yielding undefined
behavior).

Instead, we must va_copy it and hand the copy to vsnprintf,
so we always have a pristine va_list.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff King 2011-12-12 09:25:51 -05:00 committed by Junio C Hamano
parent 26db0f2e3a
commit a9bfbc5b69
1 changed files with 7 additions and 2 deletions
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9
compat/snprintf.c
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@ -19,11 +19,14 @@
#undef vsnprintf
int git_vsnprintf(char *str, size_t maxsize, const char *format, va_list ap)
{
va_list cp;
char *s;
int ret = -1;
if (maxsize > 0) {
ret = vsnprintf(str, maxsize-SNPRINTF_SIZE_CORR, format, ap);
va_copy(cp, ap);
ret = vsnprintf(str, maxsize-SNPRINTF_SIZE_CORR, format, cp);
va_end(cp);
if (ret == maxsize-1)
ret = -1;
/* Windows does not NUL-terminate if result fills buffer */
@ -42,7 +45,9 @@ int git_vsnprintf(char *str, size_t maxsize, const char *format, va_list ap)
if (! str)
break;
s = str;
ret = vsnprintf(str, maxsize-SNPRINTF_SIZE_CORR, format, ap);
va_copy(cp, ap);
ret = vsnprintf(str, maxsize-SNPRINTF_SIZE_CORR, format, cp);
va_end(cp);
if (ret == maxsize-1)
ret = -1;
}