From: "De Lara Guarch, Pablo" <pablo.de.lara.guarch@intel.com>
To: Adrien Mazarguil <adrien.mazarguil@6wind.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>,
"Doherty, Declan" <declan.doherty@intel.com>
Subject: Re: [dpdk-dev] [PATCH] cryptodev: fix compilation error in SUSE 11 SP2
Date: Wed, 5 Oct 2016 02:31:12 +0000 [thread overview]
Message-ID: <E115CCD9D858EF4F90C690B0DCB4D8973CA046C0@IRSMSX108.ger.corp.intel.com> (raw)
In-Reply-To: <20160930083359.GU17252@6wind.com>
Hi Adrien,
> -----Original Message-----
> From: Adrien Mazarguil [mailto:adrien.mazarguil@6wind.com]
> Sent: Friday, September 30, 2016 1:34 AM
> To: De Lara Guarch, Pablo
> Cc: dev@dpdk.org; Doherty, Declan
> Subject: Re: [PATCH] cryptodev: fix compilation error in SUSE 11 SP2
>
> On Thu, Sep 29, 2016 at 07:30:31PM +0000, De Lara Guarch, Pablo wrote:
> > > -----Original Message-----
> > > From: Adrien Mazarguil [mailto:adrien.mazarguil@6wind.com]
> > > Sent: Tuesday, September 27, 2016 12:45 AM
> > > To: De Lara Guarch, Pablo
> > > Cc: dev@dpdk.org; Doherty, Declan
> > > Subject: Re: [PATCH] cryptodev: fix compilation error in SUSE 11 SP2
> > >
> > > On Mon, Sep 26, 2016 at 10:50:35PM +0100, Pablo de Lara wrote:
> > > > This commit fixes following build error, which happens in SUSE 11 SP2,
> > > > with gcc 4.5.1:
> > > >
> > > > In file included from lib/librte_cryptodev/rte_cryptodev.c:71:0:
> > > > lib/librte_cryptodev/rte_cryptodev_pmd.h:76:7:
> > > > error: flexible array member in otherwise empty struct
> > > >
> > > > Fixes: 347a1e037fd3 ("lib: use C99 syntax for zero-size arrays")
> > > >
> > > > Signed-off-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>
> > >
> > > Hmm, this error message does not seem related to your patch. Assuming a
> > > similar error is caused by the original code, I think there is a more
> > > important issue as the struct should not be empty. Can you check the
> > > error?
> >
> > Well, I don't really understand what is the difference between array[] and
> array[0],
> > I thought both were the same, but some compilers only accept the latter.
>
> Before array[] got standardized by C99, a common trick was to use array[0],
> in a sense they are similar except for this one case: a struct with a single
> array[] field is explicitly not allowed in C99 since it causes the structure
> to be empty (this syntax only provides an alignment constraint for what
> follows in case padding is required), no such problem with array[0] which
> although nonstandard, is an accepted behavior, sizeof(struct foo) may yield
> 0 without complaint.
>
> > In any case, the struct will not be empty, as there are other fields, that are
> not variable sized.
> >
> > I saw that in your patch you made these two changes (among others):
> >
> > diff --git a/lib/librte_cryptodev/rte_cryptodev.h
> b/lib/librte_cryptodev/rte_cryptodev.h
> > index affbdec..1e30a19 100644
> > --- a/lib/librte_cryptodev/rte_cryptodev.h
> > +++ b/lib/librte_cryptodev/rte_cryptodev.h
> > @@ -759,7 +759,7 @@ struct rte_cryptodev_sym_session {
> > } __rte_aligned(8);
> > /**< Public symmetric session details */
> >
> > - char _private[0];
> > + char _private[];
> > /**< Private session material */
> > };
> >
> > diff --git a/lib/librte_cryptodev/rte_cryptodev_pmd.h
> b/lib/librte_cryptodev/rte_cryptodev_pmd.h
> > index 7d049ea..42e7b79 100644
> > --- a/lib/librte_cryptodev/rte_cryptodev_pmd.h
> > +++ b/lib/librte_cryptodev/rte_cryptodev_pmd.h
> > @@ -71,7 +71,7 @@ struct rte_cryptodev_session {
> > struct rte_mempool *mp;
> > } __rte_aligned(8);
> >
> > - char _private[0];
> > + __extension__ char _private[0];
> > };
> >
> > So I would expect the same change in both, as they are almost identical,
> > but you took different approaches (do you know why? I would like to know
> :))
>
> Yes, this was done to address the exact same error (probably with the same
> old GCC version (4.4.7 perhaps?)), hence my surprise to see it fixed once
> again according to your commit log, I think your only mistake was to paste
> the error message for the wrong header in there (rte_cryptodev_pmd.h
> instead
> of rte_cryptodev.h), nothing wrong with your patch besides this.
Ohhh, all right! I understand now. Will send a v2 with the commit message fixed.
Thanks!
Pablo
>
> > Basically, I noticed that gcc 4.5 doesn't complain when using your second
> approach,
> > that's why I changed it.
>
> For the record GCC wrongly thinks the structure is empty because a unnamed
> struct field is declared inside. Before C11 such declarations only created a
> new type that did not occupy any space and not an actual field, hence why it
> complains when faced with [] instead of the well-behaved [0].
>
> In this particular case it's a parsing error fixed in subsequent GCC
> versions, the unnamed struct actually uses some space otherwise it would
> have crashed during non-regression testing (right?)
>
> --
> Adrien Mazarguil
> 6WIND
next prev parent reply other threads:[~2016-10-05 2:31 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-26 21:50 Pablo de Lara
2016-09-27 7:45 ` Adrien Mazarguil
2016-09-29 19:30 ` De Lara Guarch, Pablo
2016-09-30 8:33 ` Adrien Mazarguil
2016-10-05 2:31 ` De Lara Guarch, Pablo [this message]
2016-10-05 2:45 ` [dpdk-dev] [PATCH v2] " Pablo de Lara
2016-10-05 8:51 ` Adrien Mazarguil
2016-10-06 21:00 ` De Lara Guarch, Pablo
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