[PATCH 09/20] pre-process: Avoid reading token->string on non-string tokens

[Bart Van Assche <bvanassche@acm.org>]

Check whether token_type(token) equals TOKEN_STRING before accessing
token->string->data in token_name_sequence(), and call show_token(token)
in the else branch.

Avoid dereferencing an inactive union member of struct token when
processing non-string tokens such as identifiers or punctuation in
computed or angle-bracketed #include directives, preventing undefined
pointer formation on non-pointer union payloads.

Fixes: f9d206d60eec ("Properly expand tokens on #if/#elif/#include preprocessor lines")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 pre-process.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/pre-process.c b/pre-process.c
index 038e019b11c9..7b6555677570 100644
--- a/pre-process.c
+++ b/pre-process.c
@@ -787,8 +787,10 @@ static const char *token_name_sequence(struct token *token, int endop, struct to
 
 	while (!eof_token(token) && !match_op(token, endop)) {
 		int len;
-		const char *val = token->string->data;
-		if (token_type(token) != TOKEN_STRING)
+		const char *val;
+		if (token_type(token) == TOKEN_STRING)
+			val = token->string->data;
+		else
 			val = show_token(token);
 		len = strlen(val);
 		memcpy(ptr, val, len);