Make macro expanded string immutablereview-immutable-string

The string is shared between different macro expand.
It is wrong to modify the string in place if the string
is used in a macro. Avoid overwriting the string in that
case.

Reported-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Tested-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: Christopher Li <sparse@chrisli.org>

3 files changed, 29 insertions, 11 deletions

diff --git a/char.c b/char.c
index 08ca2230..9bd3fc0d 100644
--- a/char.c
+++ b/char.c
@@ -93,6 +93,7 @@ struct token *get_string_constant(struct token *token, struct expression *expr)
 	static char buffer[MAX_STRING];
 	int len = 0;
 	int bits;
+	int esc_count = 0;
 
 	while (!done) {
 		switch (token_type(next)) {
@@ -111,6 +112,8 @@ struct token *get_string_constant(struct token *token, struct expression *expr)
 		const char *p = token->string->data;
 		const char *end = p + token->string->length - 1;
 		while (p < end) {
+			if (*p == '\\')
+				esc_count++;
 			p = parse_escape(p, &v, end, bits, token->pos);
 			if (len < MAX_STRING)
 				buffer[len] = v;
@@ -123,11 +126,13 @@ struct token *get_string_constant(struct token *token, struct expression *expr)
 		len = MAX_STRING;
 	}
 
-	if (len >= string->length)	/* can't cannibalize */
-		string = __alloc_string(len+1);
-	string->length = len+1;
-	memcpy(string->data, buffer, len);
-	string->data[len] = '\0';
+	if (esc_count || len >= string->length) {
+		if (string->immutable || len >= string->length)	/* can't cannibalize */
+			string = __alloc_string(len+1);
+		string->length = len+1;
+		memcpy(string->data, buffer, len);
+		string->data[len] = '\0';
+	}
 	expr->string = string;
 	expr->wide = is_wide;
 	return token;
diff --git a/pre-process.c b/pre-process.c
index 1aa3d2c4..5c386a85 100644
--- a/pre-process.c
+++ b/pre-process.c
@@ -209,7 +209,7 @@ static void expand_list(struct token **list)
 
 static void preprocessor_line(struct stream *stream, struct token **line);
 
-static struct token *collect_arg(struct token *prev, int vararg, struct position *pos)
+static struct token *collect_arg(struct token *prev, int vararg, struct position *pos, int count)
 {
 	struct stream *stream = input_streams + prev->pos.stream;
 	struct token **p = &prev->next;
@@ -231,6 +231,11 @@ static struct token *collect_arg(struct token *prev, int vararg, struct position
 		case TOKEN_STREAMBEGIN:
 			*p = &eof_token_entry;
 			return next;
+		case TOKEN_STRING:
+		case TOKEN_WIDE_STRING:
+			if (count > 1)
+				next->string->immutable = 1;
+			break;
 		}
 		if (false_nesting) {
 			*p = next->next;
@@ -276,7 +281,7 @@ static int collect_arguments(struct token *start, struct token *arglist, struct
 	arglist = arglist->next;	/* skip counter */
 
 	if (!wanted) {
-		next = collect_arg(start, 0, &what->pos);
+		next = collect_arg(start, 0, &what->pos, 0);
 		if (eof_token(next))
 			goto Eclosing;
 		if (!eof_token(start->next) || !match_op(next, ')')) {
@@ -286,7 +291,7 @@ static int collect_arguments(struct token *start, struct token *arglist, struct
 	} else {
 		for (count = 0; count < wanted; count++) {
 			struct argcount *p = &arglist->next->count;
-			next = collect_arg(start, p->vararg, &what->pos);
+			next = collect_arg(start, p->vararg, &what->pos, p->normal);
 			arglist = arglist->next->next;
 			if (eof_token(next))
 				goto Eclosing;
@@ -323,7 +328,7 @@ Efew:
 	goto out;
 Emany:
 	while (match_op(next, ',')) {
-		next = collect_arg(next, 0, &what->pos);
+		next = collect_arg(next, 0, &what->pos, 0);
 		count++;
 	}
 	if (eof_token(next))
@@ -1259,8 +1264,15 @@ static struct token *parse_expansion(struct token *expansion, struct token *argl
 		} else {
 			try_arg(token, TOKEN_MACRO_ARGUMENT, arglist);
 		}
-		if (token_type(token) == TOKEN_ERROR)
+		switch (token_type(token)) {
+		case TOKEN_ERROR:
 			goto Earg;
+
+		case TOKEN_STRING:
+		case TOKEN_WIDE_STRING:
+			token->string->immutable = 1;
+			break;
+		}
 	}
 	token = alloc_token(&expansion->pos);
 	token_type(token) = TOKEN_UNTAINT;
diff --git a/token.h b/token.h
index 8dbd80fd..af66b2b8 100644
--- a/token.h
+++ b/token.h
@@ -164,7 +164,8 @@ enum special_token {
 };
 
 struct string {
-	unsigned int length;
+	unsigned int length:31;
+	unsigned int immutable:1;
 	char data[];
 };