[PATCH v3 0/2] Some fixes for valgrind suppressions

[PATCH v3 0/2] Some fixes for valgrind suppressions

[David Gibson]

With the new versions of compiler and valgrind in Fedora 39, I hit
some spurious test failures.  Here are some workarounds.

Changes since v2:
 * Fix spelling error in comment
Changes since v1:
 * Took entirely different approach, fixing the existing suppression
 * Extra patch allowing optimised valgrind builds

David Gibson (2):
  valgrind: Adjust suppression for MSG_TRUNC with NULL buffer
  valgrind: Don't disable optimizations for valgrind builds

 Makefile           | 2 +-
 tcp.c              | 9 +++++++++
 test/valgrind.supp | 3 +--
 3 files changed, 11 insertions(+), 3 deletions(-)

-- 
2.41.0

[PATCH v3 1/2] valgrind: Adjust suppression for MSG_TRUNC with NULL buffer

[David Gibson]

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@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
 }
-- 
@@ -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

[PATCH v3 2/2] valgrind: Don't disable optimizations for valgrind builds

[David Gibson]

When we plan to use valgrind, we need to build passt a bit differently:
  * We need debug symbols so that valgrind can match problems it finds to
    meaningful locations
  * We need to allow additional syscalls in the seccomp filter, because
    valgrind's wrappers need them

Currently we also disable optimization (-O0).  This is unfortunate, because
it will make valgrind tests even slower than they'd otherwise be.  Worse,
it's possible that the asm behaviour without optimization might be
different enough that valgrind could miss a use of uninitialized variable
or other fault it would detect.

I suspect this was originally done because without it inlining could mean
that suppressions we use don't reliably match the places we want them to.
Alas, it turns out this is true even with -O0.  We've now implemented a
more robust workaround for this (explicit ((noinline)) attributes when
compiled with -DVALGRIND).  So, we can re-enable optimization for valgrind
builds, making them closer to regular builds.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index 57b2544..6c53695 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)) -DVALGRIND
+valgrind: FLAGS += -g -DVALGRIND
 valgrind: all
 
 .PHONY: clean
-- 
@@ -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)) -DVALGRIND
+valgrind: FLAGS += -g -DVALGRIND
 valgrind: all
 
 .PHONY: clean
-- 
2.41.0

Re: [PATCH v3 0/2] Some fixes for valgrind suppressions

[Stefano Brivio]

On Thu, 16 Nov 2023 20:15:57 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> With the new versions of compiler and valgrind in Fedora 39, I hit
> some spurious test failures.  Here are some workarounds.
> 
> Changes since v2:
>  * Fix spelling error in comment
> Changes since v1:
>  * Took entirely different approach, fixing the existing suppression
>  * Extra patch allowing optimised valgrind builds
> 
> David Gibson (2):
>   valgrind: Adjust suppression for MSG_TRUNC with NULL buffer
>   valgrind: Don't disable optimizations for valgrind builds

Applied.

-- 
Stefano