Re: [PATCH] xdiff: implement a zealous diff3

From: Felipe Contreras <felipe.contreras@gmail.com>
To: Felipe Contreras <felipe.contreras@gmail.com>,
	Jeff King <peff@peff.net>,
	Felipe Contreras <felipe.contreras@gmail.com>
Cc: git@vger.kernel.org, "Elijah Newren" <newren@gmail.com>,
	"Johannes Sixt" <j6t@kdbg.org>,
	"Sergey Organov" <sorganov@gmail.com>,
	"Junio C Hamano" <gitster@pobox.com>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Subject: Re: [PATCH] xdiff: implement a zealous diff3
Date: Sun, 13 Jun 2021 16:24:50 -0500	[thread overview]
Message-ID: <60c677a2c2d24_f5651208cf@natae.notmuch> (raw)
In-Reply-To: <60c647c1d9b5c_41f452089@natae.notmuch>

Felipe Contreras wrote:
> Jeff King wrote:
> > Try this:
> > 
> >    commit=a5170794372cf1325710a3419473c91ec4af53bf
> >    for style in merge diff3 zdiff3; do
> >      git reset --hard
> >      git checkout $commit^1
> >      git -c merge.conflictstyle=$style merge $commit^2
> >    done
> > 
> > The first two are fine; the zdiff3 one segfaults within the xmerge.c
> > code.
> 
> I can reproduct the segfault, and here is a simpler way to reproduce it:

I found the problem, m->chg0 was not initialized in xdl_refine_conflicts.

I'm not familiar with the area so I don't know if the following makes
sense, but it fixes the crash:

--- a/xdiff/xmerge.c
+++ b/xdiff/xmerge.c
@@ -333,7 +333,7 @@ static int xdl_refine_conflicts(xdfenv_t *xe1, xdfenv_t *xe2, xdmerge_t *m,
                mmfile_t t1, t2;
                xdfenv_t xe;
                xdchange_t *xscr, *x;
-               int i1 = m->i1, i2 = m->i2;
+               int i0 = m->i0, i1 = m->i1, i2 = m->i2;
 
                /* let's handle just the conflicts */
                if (m->mode)
@@ -384,6 +384,8 @@ static int xdl_refine_conflicts(xdfenv_t *xe1, xdfenv_t *xe2, xdmerge_t *m,
                        m->next = m2;
                        m = m2;
                        m->mode = 0;
+                       m->i0 = i0;
+                       m->chg0 = 0;
                        m->i1 = xscr->i1 + i1;
                        m->chg1 = xscr->chg1;
                        m->i2 = xscr->i2 + i2;


-- 
Felipe Contreras
