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From: Jeff King <peff@peff.net>
To: Junio C Hamano <gitster@pobox.com>
Cc: Stefan Beller <sbeller@google.com>, git@vger.kernel.org, orgads@gmail.com
Subject: Re: [PATCH] diff.c: increment buffer pointer in all code path
Date: Thu, 19 Oct 2017 01:42:46 -0400
Message-ID: <20171019054246.jii62lq2druohbpo@sigill.intra.peff.net> (raw)
In-Reply-To: <xmqqzi8niu1r.fsf@gitster.mtv.corp.google.com>

On Thu, Oct 19, 2017 at 02:30:08PM +0900, Junio C Hamano wrote:

> Jeff King <peff@peff.net> writes:
> 
> > it does. It just adjusts our "end pointer" to point to the last valid
> > character in the string (rather than one past), which seems to be the
> > convention that those loops (and next_byte) expect.
> 
> Yeah I am not sure if I like this comparison at the beginning of the
> function:
> 
>         static int next_byte(const char **cp, const char **endp,
>                              const struct diff_options *diffopt)
>         {
>                 int retval;
> 
>                 if (*cp > *endp)
>                         return -1;
> 
> but it says endp _is_ part of valid input, contrary to my intuition.

Actually, I think even this function is confused about its convention.
In the line you quote, we clearly treat *endp as part of the input. But
later we do:

  while (*cp < *endp && isspace(**cp))
	  (*cp)++;

meaning that we'd fail to soak up whitespace at *endp. That wouldn't be
so bad if not for the other bug which fails to eat whitespace at endp in
the first place. :)

So I think the right fix is this:

diff --git a/diff.c b/diff.c
index 6fd288420b..09081a207c 100644
--- a/diff.c
+++ b/diff.c
@@ -712,7 +712,7 @@ static int next_byte(const char **cp, const char **endp,
 {
 	int retval;
 
-	if (*cp > *endp)
+	if (*cp >= *endp)
 		return -1;
 
 	if (isspace(**cp)) {
@@ -729,7 +729,12 @@ static int next_byte(const char **cp, const char **endp,
 		if (DIFF_XDL_TST(diffopt, IGNORE_WHITESPACE)) {
 			while (*cp < *endp && isspace(**cp))
 				(*cp)++;
-			/* return the first non-ws character via the usual below */
+			/*
+			 * return the first non-ws character via the usual
+			 * below, unless we ate all of the bytes
+			 */
+			if (*cp >= *endp)
+				return -1;
 		}
 	}
 
@@ -750,9 +755,9 @@ static int moved_entry_cmp(const struct diff_options *diffopt,
 		return a->es->len != b->es->len  || memcmp(ap, bp, a->es->len);
 
 	if (DIFF_XDL_TST(diffopt, IGNORE_WHITESPACE_AT_EOL)) {
-		while (ae > ap && isspace(*ae))
+		while (ae > ap && isspace(ae[-1]))
 			ae--;
-		while (be > bp && isspace(*be))
+		while (be > bp && isspace(be[-1]))
 			be--;
 	}
 
@@ -775,7 +780,7 @@ static unsigned get_string_hash(struct emitted_diff_symbol *es, struct diff_opti
 		int c;
 
 		strbuf_reset(&sb);
-		while (ae > ap && isspace(*ae))
+		while (ae > ap && isspace(ae[-1]))
 			ae--;
 		while ((c = next_byte(&ap, &ae, o)) > 0)
 			strbuf_addch(&sb, c);

It's late here, so I'll wait for comments from Stefan and then try to
wrap it up with a commit message and test tomorrow.

-Peff

  parent reply index

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-10-12 19:53 Out of memory with diff.colormoved enabled Orgad Shaneh
2017-10-12 20:05 ` Jeff King
2017-10-12 22:39   ` Stefan Beller
2017-10-12 23:33   ` [PATCH] diff.c: increment buffer pointer in all code path Stefan Beller
2017-10-13  0:18     ` Jeff King
2017-10-13  0:20       ` Jeff King
2017-10-13  0:24         ` Stefan Beller
2017-10-19  5:04         ` Jeff King
2017-10-19  5:24           ` Jeff King
2017-10-19  5:30             ` Junio C Hamano
2017-10-19  5:32               ` Junio C Hamano
2017-10-19  5:32                 ` Jeff King
2017-10-19  5:42               ` Jeff King [this message]
2017-10-19 19:55                 ` Stefan Beller
2017-10-19 20:23                 ` [PATCH 0/5] fix "diff --color-moved --ignore-space-at-eol" Jeff King
2017-10-19 20:24                   ` [PATCH 1/5] t4015: refactor --color-moved whitespace test Jeff King
2017-10-19 20:56                     ` Stefan Beller
2017-10-19 21:10                       ` Jeff King
2017-10-19 20:25                   ` [PATCH 2/5] t4015: check "negative" case for "-w --color-moved" Jeff King
2017-10-19 20:54                     ` Stefan Beller
2017-10-19 20:26                   ` [PATCH 3/5] t4015: test the output of "diff --color-moved -b" Jeff King
2017-10-19 21:03                     ` Stefan Beller
2017-10-19 21:14                       ` Jeff King
2017-10-19 20:29                   ` [PATCH 4/5] diff: fix whitespace-skipping with --color-moved Jeff King
2017-10-19 21:15                     ` Stefan Beller
2017-10-19 21:19                       ` Jeff King
2017-10-20  7:23                     ` Simon Ruderich
2017-10-20 22:37                       ` Jeff King
2017-10-19 20:31                   ` [PATCH 5/5] diff: handle NULs in get_string_hash() Jeff King
2017-10-19 21:31                     ` Stefan Beller
2017-10-19 21:39                       ` Jeff King
2017-10-19 21:50                         ` Stefan Beller
2017-10-19 19:53             ` [PATCH] diff.c: increment buffer pointer in all code path Stefan Beller
2017-10-19 19:55               ` Jeff King

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