2 files changed, 10 insertions, 0 deletions
diff --git a/Makefile b/Makefile
index 1d45f17..d4b623f 100644
--- a/Makefile
+++ b/Makefile
@@ -50,11 +50,18 @@ HEADERS = $(PASST_HEADERS) seccomp.h
 #	https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78993
 # from the pointer arithmetic used from the tcp_tap_handler() path to get the
 # remote connection address.
+#
+# TODO: With the same combination, in ndp(), gcc optimises away the store of
+# hop_limit in the IPv6 header (temporarily set to the protocol number for
+# convenience, to mimic the ICMPv6 checksum pseudo-header) before the call to
+# csum_unaligned(). Mark csum_unaligned() as "noipa" as a quick work-around,
+# while we figure out if a corresponding gcc issue has already been reported.
 ifeq (,$(filter-out 11 12, $(shell $(CC) -dumpversion)))
 ifneq (,$(filter -flto%,$(FLAGS) $(CFLAGS)))
 ifneq (,$(filter -O2,$(FLAGS) $(CFLAGS)))
 	FLAGS += -DTCP_HASH_NOINLINE
 	FLAGS += -DSIPHASH_20B_NOINLINE
+	FLAGS += -DCSUM_UNALIGNED_NO_IPA
 endif
 endif
 endif
diff --git a/checksum.c b/checksum.c
index acb1e3e..56ad01e 100644
--- a/checksum.c
+++ b/checksum.c
@@ -97,6 +97,9 @@ uint16_t csum_fold(uint32_t sum)
  *
  * Return: 16-bit IPv4-style checksum
  */
+#if CSUM_UNALIGNED_NO_IPA
+__attribute__((__noipa__))	/* See comment in Makefile */
+#endif
 uint16_t csum_unaligned(const void *buf, size_t len, uint32_t init)
 {
 	return (uint16_t)~csum_fold(sum_16b(buf, len) + init);