Subject: Re: bug#8215: possibly uninitialized variable lower_xoff in produce_glyphless_glyph

From: Eli Zaretskii <[email-masked]>
Date: Wed, 02 Jun 2021 16:17:11 +0300

> From: Lars Ingebrigtsen <[email-masked]>
> Date: Wed, 02 Jun 2021 10:06:29 +0200
> Cc: [email-masked], Kenichi Handa <[email-masked]>
> 
> Paul Eggert <[email-masked]> writes:
> 
> > In the meantime, I plan to work around the problem by initializing
> > lower_xoff to 0, with a FIXME explaining the situation: this shouldn't
> > introduce a bug, because at worst it will replace undefined behavior
> > with defined behavior.
> 
> It looks like this code is still in place now, ten years later:
> 
> diff --git a/src/xdisp.c b/src/xdisp.c
> index 44cb713011..44a317b578 100644
> --- a/src/xdisp.c
> +++ b/src/xdisp.c
> @@ -22292,7 +22292,13 @@ produce_glyphless_glyph (struct it *it, int for_no_font, Lisp_Object acronym)
>  	  if (metrics_upper.width >= metrics_lower.width)
>  	    lower_xoff = (width - metrics_lower.width) / 2;
>  	  else
> -	    upper_xoff = (width - metrics_upper.width) / 2;
> +	    {
> +	      /* FIXME: This code doesn't look right.  It formerly was
> +		 missing the "lower_xoff = 0;", which couldn't have
> +		 been right since it left lower_xoff uninitialized.  */
> +	      lower_xoff = 0;
> +	      upper_xoff = (width - metrics_upper.width) / 2;
> +	    }
>  	}
>  
>        /* +5 is for horizontal bars of a box plus 1-pixel spaces at
> 
> Anybody have any insight into whether this is correct or not now?

I fixed this (and removed the FIXME with the incorrect
initialization).  Bottom line: it was a typo.