qapi/error: Check format string argument in error_*prepend()

error_propagate_prepend() "behaves like error_prepend()", and
error_prepend() uses "formatting @fmt, ... like printf()".
error_prepend() checks its format string argument, but
error_propagate_prepend() does not. Fix by addint the format
attribute to error_propagate_prepend() and error_vprepend().

This would have caught the bug fixed in the previous commit.

Missed in commit 4b5766488f "error: Fix use of error_prepend() with
&error_fatal, &error_abort".

Inspired-by: Stefan Weil <sw@weilnetz.de>
Suggested-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefan Weil <sw@weilnetz.de>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200723171205.14949-1-philmd@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Commit message tweaked]
Signed-off-by: Markus Armbruster <armbru@redhat.com>

diff --git a/include/qapi/error.h b/include/qapi/error.h
index 7932594dce65b1832acc15afe68b42819b52d4e8..eaa05c48374cb9aaa689f6984e56e8a1eb190da5 100644 (file)
--- a/include/qapi/error.h
+++ b/include/qapi/error.h
@@ -382,13 +382,15 @@ void error_propagate(Error **dst_errp, Error *local_err);
  * Please use ERRP_GUARD() and error_prepend() instead when possible.
  */
 void error_propagate_prepend(Error **dst_errp, Error *local_err,
-                             const char *fmt, ...);
+                             const char *fmt, ...)
+    GCC_FMT_ATTR(3, 4);
 
 /*
  * Prepend some text to @errp's human-readable error message.
  * The text is made by formatting @fmt, @ap like vprintf().
  */
-void error_vprepend(Error *const *errp, const char *fmt, va_list ap);
+void error_vprepend(Error *const *errp, const char *fmt, va_list ap)
+    GCC_FMT_ATTR(2, 0);
 
 /*
  * Prepend some text to @errp's human-readable error message.