Even after bug 1060419 lands, there will be a call to PR_vsnprintf in webmdemux_log. One way to fix this would be to change the code a bit to use SprintfLiteral just to print the incoming arguments; then do the extra printing directly in the invocation of MOZ_LOG. However, in order to do this properly, first nestegg must be fixed to add the appropriate printf attribute. I gave this a whirl and it showed that nestegg seems to be assuming an NSPR-like printf. You can try it upstream like: diff --git a/include/nestegg/nestegg.h b/include/nestegg/nestegg.h index d91483b..102e2fc 100644 --- a/include/nestegg/nestegg.h +++ b/include/nestegg/nestegg.h @@ -159,8 +159,15 @@ typedef struct { uint64_t seek_preroll;/**< Nanoseconds that must be discarded after a seek. */ } nestegg_audio_params; +#if __GNUC__ +#define NESTEGG_PRINTF(x, y) __attribute__((format(printf, x, y))) +#else +#define NESTEGG_PRINTF(x, y) +#endif + /** Logging callback function pointer. */ -typedef void (* nestegg_log)(nestegg * context, unsigned int severity, char const * format, ...); +typedef void (* nestegg_log)(nestegg * context, unsigned int severity, char const * format, ...) + NESTEGG_PRINTF(3, 4); /** Initialize a nestegg context. During initialization the parser will read forward in the stream processing all elements until the first

We're rewriting nestegg in Rust so this probably isn't worth doing.