[PATCH v4 3/3] regex: use regexec_buf()

[Johannes Schindelin <johannes.schindelin@gmx.de>]

The new regexec_buf() function operates on buffers with an explicitly
specified length, rather than NUL-terminated strings.

We need to use this function whenever the buffer we want to pass to
regexec() may have been mmap()ed (and is hence not NUL-terminated).

Note: the original motivation for this patch was to fix a bug where
`git diff -G <regex>` would crash. This patch converts more callers,
though, some of which explicitly allocated and constructed
NUL-terminated strings (or worse: modified read-only buffers to insert
NULs).

Some of the buffers actually may be NUL-terminated. As regexec_buf()
uses REG_STARTEND where available, but has to fall back to allocating
and constructing NUL-terminated strings where REG_STARTEND is not
available, this makes the code less efficient in the latter case.

However, given the widespread support for REG_STARTEND, combined with
the improved ease of code maintenance, we strike the balance in favor
of REG_STARTEND.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 diff.c                  |  3 ++-
 diffcore-pickaxe.c      | 18 ++++++++----------
 grep.c                  | 14 ++------------
 t/t4061-diff-pickaxe.sh |  2 +-
 xdiff-interface.c       | 13 ++++---------
 5 files changed, 17 insertions(+), 33 deletions(-)

diff --git a/diff.c b/diff.c
index c6da383..fb99235 100644
--- a/diff.c
+++ b/diff.c
@@ -952,7 +952,8 @@ 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)) {
+		if (!regexec_buf(word_regex, buffer->ptr + *begin,
+				 buffer->size - *begin, 1, match, 0)) {
 			char *p = memchr(buffer->ptr + *begin + match[0].rm_so,
 					'\n', match[0].rm_eo - match[0].rm_so);
 			*end = p ? p - buffer->ptr : match[0].rm_eo + *begin;
diff --git a/diffcore-pickaxe.c b/diffcore-pickaxe.c
index 55067ca..9795ca1 100644
--- a/diffcore-pickaxe.c
+++ b/diffcore-pickaxe.c
@@ -23,7 +23,6 @@ static void diffgrep_consume(void *priv, char *line, unsigned long len)
 {
 	struct diffgrep_cb *data = priv;
 	regmatch_t regmatch;
-	int hold;
 
 	if (line[0] != '+' && line[0] != '-')
 		return;
@@ -33,11 +32,8 @@ static void diffgrep_consume(void *priv, char *line, unsigned long len)
 		 * caller early.
 		 */
 		return;
-	/* Yuck -- line ought to be "const char *"! */
-	hold = line[len];
-	line[len] = '\0';
-	data->hit = !regexec(data->regexp, line + 1, 1, &regmatch, 0);
-	line[len] = hold;
+	data->hit = !regexec_buf(data->regexp, line + 1, len - 1, 1,
+				 &regmatch, 0);
 }
 
 static int diff_grep(mmfile_t *one, mmfile_t *two,
@@ -50,9 +46,11 @@ static int diff_grep(mmfile_t *one, mmfile_t *two,
 	xdemitconf_t xecfg;
 
 	if (!one)
-		return !regexec(regexp, two->ptr, 1, &regmatch, 0);
+		return !regexec_buf(regexp, two->ptr, two->size,
+				    1, &regmatch, 0);
 	if (!two)
-		return !regexec(regexp, one->ptr, 1, &regmatch, 0);
+		return !regexec_buf(regexp, one->ptr, one->size,
+				    1, &regmatch, 0);
 
 	/*
 	 * We have both sides; need to run textual diff and see if
@@ -83,8 +81,8 @@ static unsigned int contains(mmfile_t *mf, regex_t *regexp, kwset_t kws)
 		regmatch_t regmatch;
 		int flags = 0;
 
-		assert(data[sz] == '\0');
-		while (*data && !regexec(regexp, data, 1, &regmatch, flags)) {
+		while (*data &&
+		       !regexec_buf(regexp, data, sz, 1, &regmatch, flags)) {
 			flags |= REG_NOTBOL;
 			data += regmatch.rm_eo;
 			if (*data && regmatch.rm_so == regmatch.rm_eo)
diff --git a/grep.c b/grep.c
index d7d00b8..1194d35 100644
--- a/grep.c
+++ b/grep.c
@@ -898,17 +898,6 @@ static int fixmatch(struct grep_pat *p, char *line, char *eol,
 	}
 }
 
-static int regmatch(const regex_t *preg, char *line, char *eol,
-		    regmatch_t *match, int eflags)
-{
-#ifdef REG_STARTEND
-	match->rm_so = 0;
-	match->rm_eo = eol - line;
-	eflags |= REG_STARTEND;
-#endif
-	return regexec(preg, line, 1, match, eflags);
-}
-
 static int patmatch(struct grep_pat *p, char *line, char *eol,
 		    regmatch_t *match, int eflags)
 {
@@ -919,7 +908,8 @@ static int patmatch(struct grep_pat *p, char *line, char *eol,
 	else if (p->pcre_regexp)
 		hit = !pcrematch(p, line, eol, match, eflags);
 	else
-		hit = !regmatch(&p->regexp, line, eol, match, eflags);
+		hit = !regexec_buf(&p->regexp, line, eol - line, 1, match,
+				   eflags);
 
 	return hit;
 }
diff --git a/t/t4061-diff-pickaxe.sh b/t/t4061-diff-pickaxe.sh
index 5929f2e..f0bf50b 100755
--- a/t/t4061-diff-pickaxe.sh
+++ b/t/t4061-diff-pickaxe.sh
@@ -14,7 +14,7 @@ test_expect_success setup '
 	test_tick &&
 	git commit -m "A 4k file"
 '
-test_expect_failure '-G matches' '
+test_expect_success '-G matches' '
 	git diff --name-only -G "^0{4096}$" HEAD^ >out &&
 	test 4096-zeroes.txt = "$(cat out)"
 '
diff --git a/xdiff-interface.c b/xdiff-interface.c
index 3bfc69c..060038c 100644
--- a/xdiff-interface.c
+++ b/xdiff-interface.c
@@ -214,11 +214,10 @@ struct ff_regs {
 static long ff_regexp(const char *line, long len,
 		char *buffer, long buffer_size, void *priv)
 {
-	char *line_buffer;
 	struct ff_regs *regs = priv;
 	regmatch_t pmatch[2];
 	int i;
-	int result = -1;
+	int result;
 
 	/* Exclude terminating newline (and cr) from matching */
 	if (len > 0 && line[len-1] == '\n') {
@@ -228,18 +227,16 @@ static long ff_regexp(const char *line, long len,
 			len--;
 	}
 
-	line_buffer = xstrndup(line, len); /* make NUL terminated */
-
 	for (i = 0; i < regs->nr; i++) {
 		struct ff_reg *reg = regs->array + i;
-		if (!regexec(&reg->re, line_buffer, 2, pmatch, 0)) {
+		if (!regexec_buf(&reg->re, line, len, 2, pmatch, 0)) {
 			if (reg->negate)
-				goto fail;
+				return -1;
 			break;
 		}
 	}
 	if (regs->nr <= i)
-		goto fail;
+		return -1;
 	i = pmatch[1].rm_so >= 0 ? 1 : 0;
 	line += pmatch[i].rm_so;
 	result = pmatch[i].rm_eo - pmatch[i].rm_so;
@@ -248,8 +245,6 @@ static long ff_regexp(const char *line, long len,
 	while (result > 0 && (isspace(line[result - 1])))
 		result--;
 	memcpy(buffer, line, result);
- fail:
-	free(line_buffer);
 	return result;
 }
 
-- 
2.10.0.windows.1.10.g803177d