Subject: Re: [PATCH 11/11] bug_fl(): add missing `va_end()` call

From: Junio C Hamano <[email-masked]>
Date: Wed, 15 Jun 2022 22:00:14 -0700

Jeff King <[email-masked]> writes:

> On Wed, Jun 15, 2022 at 11:35:45PM +0000, Johannes Schindelin via GitGitGadget wrote:
>
>> From: Johannes Schindelin <[email-masked]>
>> 
>> According to the manual:
>> 
>> 	Each invocation of va_copy() must be matched by a corresponding
>> 	invocation of va_end() in the  same function.
>> 
>> Note: There is another instance of `va_copy()` in `usage.c` that is
>> missing a `va_end()` call, in `BUG_vfl()`. It does not matter there,
>> though, because that function either `exit()`s or `abort()`s, anyway.
>> 
>> Reported by Coverity.
>
> This was introduced by the recent 0cc05b044f (usage.c: add a non-fatal
> bug() function to go with BUG(), 2022-06-02). But there's a much worse
> bug in the same function. The code introduced by that patch does:
>
>   va_list ap, cp;
>   [...]
>   va_copy(cp, ap);
>   va_start(ap, fmt);
>
> So "cp" is copied from "ap" before we have actually initialized "ap".
> It's surprising that this works at all. The two lines should be flipped.

Yes, it is surprising.  Perhaps it is not working at all.

Thanks for an extra set of eyeballs.

> IMHO, since we're in the actual varargs function itself, it would be
> simpler to just bracket each use with start/end, rather than copying,
> like:
>
> diff --git a/usage.c b/usage.c
> index 79900d0287..56e29d6cd6 100644
> --- a/usage.c
> +++ b/usage.c
> @@ -334,15 +334,17 @@ NORETURN void BUG_fl(const char *file, int line, const char *fmt, ...)
>  int bug_called_must_BUG;
>  void bug_fl(const char *file, int line, const char *fmt, ...)
>  {
> -	va_list ap, cp;
> +	va_list ap;
>  
>  	bug_called_must_BUG = 1;
>  
> -	va_copy(cp, ap);
>  	va_start(ap, fmt);
>  	BUG_vfl_common(file, line, fmt, ap);
>  	va_end(ap);
> -	trace2_cmd_error_va(fmt, cp);
> +
> +	va_start(ap, fmt);
> +	trace2_cmd_error_va(fmt, ap);
> +	va_end(ap);
>  }
>  
>  #ifdef SUPPRESS_ANNOTATED_LEAKS
>
> but I am happy with any solution that is correct. :)
>
> -Peff