OK. Since I found the letter in bug-diffutils is kind of messy, I rephrase
our findings as below:
We isolated the failure-inducing change introduced by diffutils-2.9:
diff -u ./diffutils-2.8.1/src/io.c ./diffutils-2.9/src/io.c
--- diffutils-2.8.1/src/io.c
+++ diffutils-2.9/src/io.c
@@ -664,2 +650,2 @@
- for (; p0 != beg0; p0--, p1--)
- if (*p0 != *p1)
+ while (p0 != beg0)
+ if (*--p0 != *--p1)
{
/* Point at the first char of the matching suffix. */
+ ++p0, ++p1;
beg0 = p0;
break;
}
This change causes the pointer 'p0' wrongly points to somewhere
different as it does in 2.8.after the loop, and later defines the variable
filevec[0].suffix_begin, which leads to a failure in 2.9.
in diffutils-2.9/src/io.c:
static void
find_identical_ends (struct file_data filevec[])
{
...
if (! ROBUST_OUTPUT_STYLE (output_style)
|| filevec[0].missing_newline == filevec[1].missing_newline)
{
...
while (p0 != beg0)
if (*--p0 != *--p1)
{
...
}
...
}
/* Record the suffix. */
filevec[0].suffix_begin = p0;
filevec[1].suffix_begin = p1;
...
}
We also notice that in 3.0 this bug has been fixed by adding the following
code:
diff -u ./diffutils-2.9/src/io.c ./diffutils-3.0/src/io.c
--- diffutils-2.9/src/io.c
+++ diffutils-3.0/src/io.c
@@ -471,7 +470,13 @@
linbuf[line] = p;
if (p == bufend)
- break;
+ {
+ /* If the last line is incomplete and we do not silently
+ complete lines, don't count its appended newline. */
+ if (current->missing_newline && ROBUST_OUTPUT_STYLE
(output_style))
+ linbuf[line]--;
+ break;
+ }
if (context <= i && no_diff_means_no_output)
break;
This repair does fix the bug. However, this fix tries to adjust the
final linbuf[line] setting rather than corrects the error cause. Instead, we
suggest withdraw the change introduced in 2.9 may be a better choice.
Besides, the value of filevec[0].suffix_begin in 3.0 is not equal to that in
2.8.1, which may cause potential bugs in the future.
2010/10/7 Jim Meyering <[email protected]>
> Kai YU wrote:
> > Dear Jim:
>
> Thank you for taking the time to analyze diffutils bugs.
> Please send any such mail to the bug-reporting address
> you see in diff --help output: [email protected]
>
> > I and my colleague Xiangyu Zhang and Jin Chen recently examined
> Bug#
> > 577832 in our study. Since this bug is a regression from diffutils-2.8.1,
> we
> > isolated the failure-inducing change automatically:
> >
> > diff -u ./diffutils-2.8.1/src/io.c ./diffutils-2.9/src/io.c
> > --- diffutils-2.8.1/src/io.c
> > +++ diffutils-2.9/src/io.c
> > @@ -664,2 +650,2 @@
> > - for (; p0 != beg0; p0--, p1--)
> > - if (*p0 != *p1)
> > + while (p0 != beg0)
> > + if (*--p0 != *--p1)
> > {
> > /* Point at the first char of the matching suffix. */
> > + ++p0, ++p1;
> > beg0 = p0;
> > break;
> > }
> >
> > This change causes the pointer 'p0' wrongly points to somewhere
> different
> > as it does in 2.8.after the loop, and later defines the variable filevec
> > [0].suffix_begin, which leads to a failure in 2.9.
> >
> > in diffutils-2.9/src/io.c:
> >
> > static void
> > find_identical_ends (struct file_data filevec[])
> > {
> > ...
> > if (! ROBUST_OUTPUT_STYLE (output_style)
> > || filevec[0].missing_newline == filevec[1].missing_newline)
> > {
> > ...
> > while (p0 != beg0)
> > if (*--p0 != *--p1)
> > {
> > ...
> > }
> > ...
> > }
> > /* Record the suffix. */
> > filevec[0].suffix_begin = p0;
> > filevec[1].suffix_begin = p1;
> > ...
> > }
> >
> > We also notice that in 3.0 this bug has been fixed by adding the
> > following code:
> >
> > diff -u ./diffutils-2.9/src/io.c ./diffutils-3.0/src/io.c
> > --- diffutils-2.9/src/io.c
> > +++ diffutils-3.0/src/io.c
> > @@ -471,7 +470,13 @@
> >
> > linbuf[line] = p;
> >
> > if (p == bufend)
> > - break;
> > + {
> > + /* If the last line is incomplete and we do not silently
> > + complete lines, don't count its appended newline. */
> > + if (current->missing_newline && ROBUST_OUTPUT_STYLE
> > (output_style))
> > + linbuf[line]--;
> > + break;
> > + }
> >
> > if (context <= i && no_diff_means_no_output)
> > break;
> >
> > This repair does fix the bug. However, this fix tries to adjust
> the
> > final linbuf[line] setting rather than corrects the error cause.
> > Instead, we suggest withdraw the change introduced in 2.9 may be a better
> > choice. Besides, the value of filevec[0].suffix_begin in 3.0 is not equal
> to
> > that in 2.8.1, which may cause potential bugs in the future.
> >
> > Looking forward to your reply.
> > ---
> > Kai YU
>
