[PATCH] checkpatch: handle token pasting better

From: Paolo Bonzini
Date: Wed Jul 04 2018 - 12:12:09 EST

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 {
- \#|
- \#\#|
- ^(?:typedef|struct|enum)\b
+ ^(?:typedef|struct|enum)\b|
+ ^\#
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);