Re: [PATCH 2/3] diff_populate_filespec: NUL-terminate buffers

From: Jeff King <peff@peff.net>
Date: Sep 8, 2016, 08:22 UTC
Message-ID: <20160908082246.saf7vlw2xgjo7jvg@sigill.intra.peff.net>
In-Reply-To: <alpine.DEB.2.20.1609080933470.129229@virtualbox>

On Thu, Sep 08, 2016 at 09:49:38AM +0200, Johannes Schindelin wrote:

Show 22 quoted lines

> > > diff --git a/diff.c b/diff.c
> > > index 534c12e..2c5a360 100644
> > > --- a/diff.c
> > > +++ b/diff.c
> > > @@ -951,7 +951,13 @@ static int find_word_boundaries(mmfile_t *buffer,
> > > regex_t *word_regex,
> > >  {
> > >  	if (word_regex && *begin < buffer->size) {
> > >  		regmatch_t match[1];
> > > -		if (!regexec(word_regex, buffer->ptr + *begin, 1, match,
> > > 		0)) {
> > > +		int f = 0;
> > > +#ifdef REG_STARTEND
> > > +		match[0].rm_so = 0;
> > > +		match[0].rm_eo = *end - *begin;
> > > +		f = REG_STARTEND;
> > > +#endif
> > > +		if (!regexec(word_regex, buffer->ptr + *begin, 1, match,
> > > f)) {
> 
> Heh. You introduced the same bug I did. Or maybe you just fetched my
> mmap-regexec branch and looked at an intermediate iteration?

I do not think I introduced anything. The quoted text is what you sent. Which is perhaps why it has your bug. :)

Show 9 quoted lines

> > But I much prefer this approach to copying the data just to add a NUL.
> 
> I think it is not worth the burden. The only regex implementation in
> semi-widespread use that do not support REG_STARTEND seems to be musl.
> 
> I'd rather not spend *so much* effort just to support an obscure platform.
> Not when the users of that obscure platform could spend that effort
> themselves. And probably won't, because we only copy data to add a NUL on
> those platforms when regexec() is called on an mmfile_t.

I'm confused about what you think I'm proposing. I was saying I _like_ something like regexec_buf() instead of copying the data. Which seems like the simpler thing to me (and presumably to you). Or do you mean using compat/regex to build on re_search() consistently? I do not think that is all that complex; the question is only whether people really want to use their own regex libraries.

Between the two options for regexec_buf(), I think you have convinced me that REG_STARTEND is better than just using compat/regex everywhere. I do think the fallback for platforms like musl should be "use compat/regex" and not doing an expensive copy (which in most cases is not even necessary).

-Peff