valgrind complains if we pass a NULL buffer to recv(), even if we use
MSG_TRUNC, in which case it's actually safe. For a long time we've had
a valgrind suppression for this. It singles out the recv() in
tcp_sock_consume(), the only place we use MSG_TRUNC.
However, tcp_sock_consume() only has a single caller, which makes it a
prime candidate for inlining. If inlined, it won't appear on the stack and
valgrind won't match the correct suppression.
It appears that certain compiler versions (for example gcc-13.2.1 in
Fedora 39) will inline this function even with the -O0 we use for valgrind
builds. This breaks the suppression leading to a spurious failure in the
tests.
There's not really any way to adjust the suppression itself without making
it overly broad (we don't want to match other recv() calls). So, as a hack
explicitly prevent inlining of this function when we're making a valgrind
build. To accomplish this add an explicit -DVALGRIND when making such a
build.
Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
---
Makefile | 2 +-
tcp.c | 9 +++++++++
test/valgrind.supp | 3 +--
3 files changed, 11 insertions(+), 3 deletions(-)
diff --git a/Makefile b/Makefile
index ff21459..57b2544 100644
--- a/Makefile
+++ b/Makefile
@@ -128,7 +128,7 @@ qrap: $(QRAP_SRCS) passt.h
valgrind: EXTRA_SYSCALLS += rt_sigprocmask rt_sigtimedwait rt_sigaction \
getpid gettid kill clock_gettime mmap \
munmap open unlink gettimeofday futex
-valgrind: FLAGS:=-g -O0 $(filter-out -O%,$(FLAGS))
+valgrind: FLAGS:=-g -O0 $(filter-out -O%,$(FLAGS)) -DVALGRIND
valgrind: all
.PHONY: clean
diff --git a/tcp.c b/tcp.c
index cfcd40a..b2e9bb8 100644
--- a/tcp.c
+++ b/tcp.c
@@ -2097,6 +2097,15 @@ static void tcp_conn_from_tap(struct ctx *c,
*
* Return: 0 on success, negative error code from recv() on failure
*/
+#ifdef VALGRIND
+/* valgrind doesn't realise that passing a NULL buffer to recv() is ok if using
+ * MSG_TRUNC. We have a suppression for this in the tests, but it relies on
+ * valgrind being able to see the tcp_sock_consume() stack frame, which it won't
+ * if this gets inlined. This has a single caller making it a likely inlining
+ * candidate, and certain compiler versions will do so even at -O0.
+ */
+ __attribute__((noinline))
+#endif /* VALGRIND */
static int tcp_sock_consume(const struct tcp_tap_conn *conn, uint32_t ack_seq)
{
/* Simply ignore out-of-order ACKs: we already consumed the data we
diff --git a/test/valgrind.supp b/test/valgrind.supp
index 1228056..a158394 100644
--- a/test/valgrind.supp
+++ b/test/valgrind.supp
@@ -3,7 +3,6 @@
passt_recv_MSG_TRUNC_into_NULL_buffer
Memcheck:Param
socketcall.recvfrom(buf)
- fun:recv
...
- fun:tcp_sock_consume*
+ fun:tcp_sock_consume
}
--
2.41.0