Re: [PATCH v2 1/2] valgrind: Adjust suppression for MSG_TRUNC with NULL buffer

[David Gibson <david@gibson.dropbear.id.au>]

[-- Attachment #1: Type: text/plain, Size: 2826 bytes --]

On Thu, Nov 16, 2023 at 08:21:34AM +0100, Stefano Brivio wrote:
> On Thu, 16 Nov 2023 16:43:49 +1100
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > 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..b86d433 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 supression for this in the tests, but it relies on
>                               ^ pp
> 
> (I can fix it up on merge but I guess you prefer to repost). Rest of the
> series looks good to me.

Oops, yes.  Resent.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]