Makefile: cppcheck target: Suppress unmatchedSuppression, pass CFLAGS

Some of those warnings don't trigger even on systems with very
similar toolchains, suppress unmatchedSuppression warnings, they're
basically useless.

While at it, pass CFLAGS to cppcheck.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Makefile

@@ -14,6 +14,7 @@ CFLAGS += -DRLIMIT_STACK_VAL=$(shell ulimit -s)
 CFLAGS += -DPAGE_SIZE=$(shell getconf PAGE_SIZE)
 CFLAGS += -DNETNS_RUN_DIR=\"/run/netns\"
 CFLAGS += -DPASST_AUDIT_ARCH=AUDIT_ARCH_$(shell uname -m | tr [a-z] [A-Z])
+CFLAGS += -DARCH=\"$(shell uname -m)\"
 
 # On gcc 11.2, with -O2 and -flto, tcp_hash() and siphash_20b(), if inlined,
 # seem to be hitting something similar to:
@@ -59,7 +60,7 @@ passt4netns: passt
 	ln -s passt passt4netns
 
 qrap: qrap.c passt.h
-	$(CC) $(CFLAGS) -DARCH=\"$(shell uname -m)\" \
+	$(CC) $(CFLAGS) \
 		qrap.c -o qrap
 
 .PHONY: clean
@@ -176,20 +177,32 @@ cppcheck: $(wildcard *.c) $(wildcard *.h)
 	cppcheck --std=c99 --error-exitcode=1 --enable=all --force	\
 	--inconclusive --library=posix					\
 	-I/usr/include $(EXTRA_INCLUDES_OPT)				\
+									\
+	--suppress=syntaxError:/usr/include/stdlib.h			\
 	--suppress=missingIncludeSystem					\
 	--suppress="*:$(EXTRA_INCLUDES)/avx512fintrin.h"		\
 	--suppress="*:$(EXTRA_INCLUDES)/xmmintrin.h"			\
 	--suppress="*:$(EXTRA_INCLUDES)/emmintrin.h"			\
 	--suppress="*:$(EXTRA_INCLUDES)/avxintrin.h"			\
 	--suppress="*:$(EXTRA_INCLUDES)/bmiintrin.h"			\
+									\
 	--suppress=objectIndex:tcp.c --suppress=objectIndex:udp.c	\
 	--suppress=va_list_usedBeforeStarted:util.c			\
-	--suppress=unusedFunction:igmp.c				\
-	--suppress=unusedFunction:siphash.c				\
+	--suppress=unusedFunction					\
 	--suppress=knownConditionTrueFalse:conf.c			\
 	--suppress=strtokCalled:conf.c --suppress=strtokCalled:qrap.c	\
 	--suppress=getpwnamCalled:passt.c				\
 	--suppress=localtimeCalled:pcap.c				\
 	--suppress=unusedStructMember:pcap.c				\
 	--suppress=funcArgNamesDifferent:util.h				\
+									\
+	--suppress=unmatchedSuppression:conf.c				\
+	--suppress=unmatchedSuppression:passt.c				\
+	--suppress=unmatchedSuppression:pcap.c				\
+	--suppress=unmatchedSuppression:qrap.c				\
+	--suppress=unmatchedSuppression:tcp.c				\
+	--suppress=unmatchedSuppression:udp.c				\
+	--suppress=unmatchedSuppression:util.c				\
+	--suppress=unmatchedSuppression:util.h				\
+	$(filter -D%,$(CFLAGS))						\
 	.

ndp.c

@@ -140,7 +140,7 @@ int ndp(struct ctx *c, struct ethhdr *eh, size_t len)
 
 		for (n = 0; *c->dns_search[n].n; n++)
 			dns_s_len += strlen(c->dns_search[n].n) + 2;
-		if (len) {
+		if (dns_s_len) {
 			*p++ = 31;			/* DNSSL */
 			*p++ = (len + 8 - 1) / 8 + 1;	/* length */
 			p += 2;				/* reserved */