[libcpp] Fix ICE with conditional macros (PR preprocessor/61977)

[libcpp] Fix ICE with conditional macros (PR preprocessor/61977)

[Jakub Jelinek]

Hi!

cpp_peek_token is broken whenever it sees CPP_EOF, as it doesn't back up
the previous tokens (if any) and the CPP_EOF token, so for callers
of cpp_peek_token whenever it returns CPP_EOF it is a fatal condition,
so one really can't peek safely.

cpp_peek_token has apparently been written for the conditional macros
where it really assumes one can safely peek tokens several times.

The following patch fixes that.  If no CPP_EOF is seen or it is seen on the
last token, index will be -1 and thus count - index is still count + 1
as before, but if we hit CPP_EOF earlier, we only back up tokens before
that.

Richard and Prathamesh raised this issue already some time ago:
https://gcc.gnu.org/ml/gcc-patches/2014-08/msg00895.html
but there was no follow-up on that.

Bootstrapped/regtested on powerpc64{,le}-linux and {x86_64,i686}-linux, ok
for trunk?

2015-03-31  Jakub Jelinek  <jakub@redhat.com>

	PR preprocessor/61977
	* lex.c (cpp_peek_token): If peektok is CPP_EOF, back it up
	with all tokens peeked by the current function.

--- libcpp/lex.c.jj	2015-03-17 18:10:12.000000000 +0100
+++ libcpp/lex.c	2015-03-31 19:39:28.207748285 +0200
@@ -2084,11 +2084,14 @@ cpp_peek_token (cpp_reader *pfile, int i
     {
       peektok = _cpp_lex_token (pfile);
       if (peektok->type == CPP_EOF)
-	return peektok;
+	{
+	  index--;
+	  break;
+	}
     }
   while (index--);
 
-  _cpp_backup_tokens_direct (pfile, count + 1);
+  _cpp_backup_tokens_direct (pfile, count - index);
   pfile->keep_tokens--;
 
   return peektok;
--- gcc/testsuite/gcc.dg/cpp/pr61977.c.jj	2015-03-31 19:46:12.226279905 +0200
+++ gcc/testsuite/gcc.dg/cpp/pr61977.c	2015-03-31 19:46:03.638417398 +0200
@@ -0,0 +1,4 @@
+/* PR preprocessor/61977 */
+/* { dg-do preprocess } */
+
+vector

	Jakub

Re: [libcpp] Fix ICE with conditional macros (PR preprocessor/61977)

[Jason Merrill]

OK.

Jason