Add __attribute__(format)s for our varargs printf/scanf wrappers

It turns out that if you set the third argument of
__attribute__(format) to 0, GCC and Clang will check the format
argument without expecting to find variadic arguments.  This is the
correct behavior for vsnprintf, vasprintf, and vscanf.

I'm hoping this will fix bug 5969 (a clang warning) by telling clang that
the format argument to tor_vasprintf is indeed a format string.

1 files changed, 3 insertions, 2 deletions

diff --git a/src/common/compat.h b/src/common/compat.h
index d2f1fd1295..fc70caf50c 100644
--- a/src/common/compat.h
+++ b/src/common/compat.h
@@ -261,11 +261,12 @@ void tor_munmap_file(tor_mmap_t *handle) ATTR_NONNULL((1));
 int tor_snprintf(char *str, size_t size, const char *format, ...)
   CHECK_PRINTF(3,4) ATTR_NONNULL((1,3));
 int tor_vsnprintf(char *str, size_t size, const char *format, va_list args)
-  ATTR_NONNULL((1,3));
+  CHECK_PRINTF(3,0) ATTR_NONNULL((1,3));
 
 int tor_asprintf(char **strp, const char *fmt, ...)
   CHECK_PRINTF(2,3);
-int tor_vasprintf(char **strp, const char *fmt, va_list args);
+int tor_vasprintf(char **strp, const char *fmt, va_list args)
+  CHECK_PRINTF(2,0);
 
 const void *tor_memmem(const void *haystack, size_t hlen, const void *needle,
                        size_t nlen)  ATTR_PURE ATTR_NONNULL((1,3));