[PATCH] checkpatch: handle token pasting better

[Paolo Bonzini]

The mechanism to find possible type tokens can sometimes be confused and go into an
infinite loop.  This happens for example in QEMU for a line that looks like

         uint## BITS ##_t S = _S, T = _T;                            \
         uint## BITS ##_t as, at, xs, xt, xd;                        \

Because the token pasting operator does not have a space before _t, it does not
match $notPermitted.  However, (?x) is turned on in the regular expression for
modifiers, and thus ##_t matches the empty string.  As a result, annotate_values
goes in an infinite loop.

The solution is simply to remove token pasting operators from the string before
looking for modifiers.  In the example above, the string uintBITS_t will be
evaluated as a candidate modifier.  This works as long as people do not
write things like a##s##m (and fails safely with a false negative if
they do), and it fits nicely into sub possible.

For a similar reason, \# should be rejected always, even if it is not
at end of line or followed by whitespace.

Reported-by: Aleksandar Markovic <amarkovic@xxxxxxxxxxxx>
Fixes: 89a883530fe7 ("checkpatch: ## is not a valid modifier")
Cc: Joe Perches <joe@xxxxxxxxxxx>
Cc: Andy Whitcroft <apw@xxxxxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 scripts/checkpatch.pl | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index a9c05506e325..0cd8307575e6 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -1915,10 +1915,9 @@ sub possible {
 			else|
 			asm|__asm__|
 			do|
-			\#|
-			\#\#|
 		)(?:\s|$)|
-		^(?:typedef|struct|enum)\b
+		^(?:typedef|struct|enum)\b|
+		^\#
 	    )}x;
 	warn "CHECK<$possible> ($line)\n" if ($dbg_possible > 2);
 	if ($possible !~ $notPermitted) {
@@ -1928,7 +1927,7 @@ sub possible {
 		if ($possible =~ /^\s*$/) {
 
 		} elsif ($possible =~ /\s/) {
-			$possible =~ s/\s*$Type\s*//g;
+			$possible =~ s/\s*(?:$Type|\#\#)\s*//g;
 			for my $modifier (split(' ', $possible)) {
 				if ($modifier !~ $notPermitted) {
 					warn "MODIFIER: $modifier ($possible) ($line)\n" if ($dbg_possible);
-- 
2.17.1