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Date: Sat, 22 Jun 2019 12:17:00 -0400
From: Neil Horman <nhorman@tuxdriver.com>
To: David Marchand <david.marchand@redhat.com>
Cc: Aaron Conole <aconole@redhat.com>,
Adrien Mazarguil <adrien.mazarguil@6wind.com>,
Gage Eads <gage.eads@intel.com>, dev <dev@dpdk.org>,
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Pablo de Lara <pablo.de.lara.guarch@intel.com>
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Subject: Re: [dpdk-dev] [PATCH] eal: promote some service core functions to
stable
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On Fri, Jun 21, 2019 at 09:58:41PM +0200, David Marchand wrote:
> On Fri, Jun 21, 2019 at 7:41 PM Neil Horman <nhorman@tuxdriver.com> wrote:
>
> > On Fri, Jun 21, 2019 at 06:47:31PM +0200, David Marchand wrote:
> > > On Fri, Jun 21, 2019 at 6:28 PM Neil Horman <nhorman@tuxdriver.com>
> > wrote:
> > >
> > > > On Fri, Jun 21, 2019 at 02:45:45PM +0200, David Marchand wrote:
> > > > > Ok, did a new pass on the tree.. found quite some sites where we have
> > > > > issues (and other discrepancies... I started a new patchset).
> > > > > Looked at gcc documentation [1], and to me the safer approach would
> > be to
> > > > > enforce that __rte_experimental is the first thing of a symbol
> > > > declaration.
> > > > >
> > > > > Comments?
> > > > >
> > > > Yes, thats the only way it works, in fact I'm suprised gcc didn't
> > throw an
> > > > error
> > > > about expecting an asm statement if you put it anywhere else
> > > >
> > >
> > > - I tried this, but then I hit issues with inlines.
> > > Like for example:
> > >
> > > static inline char * __rte_experimental
> > > rte_mbuf_buf_addr(struct rte_mbuf *mb, struct rte_mempool *mp)
> > > {
> > > return (char *)mb + sizeof(*mb) + rte_pktmbuf_priv_size(mp);
> > > }
> > >
> > > I did not find a way to move the __rte_experimental tag without getting
> > > warnings.
> > Right, thats the way its supposed to work on gcc/icc/clang. function
> > attributes
> > must be declared between the return type and the function name, anything
> > else
> > will generate compiler warnings/errors. Because __rte_experimental
> > expands to a
> > __attribute__(...), you have to place it there.
> >
> > > If I try to compile some sources which includes rte_mbuf.h but without
> > > -DALLOW_EXPERIMENTAL_API, then gcc errors at including the header,
> > > complaining that rte_mbuf_buf_addr() is deprecated, even if this inline
> > is
> > > not called.
> > >
> > Thats...odd. I wonder if thats an artifact of the function being marked as
> > inline. The compiler is supposed to insert the warning for any remaining
> > calls
> > after dead code eliminitaion. If the function is inline, I wonder if the
> > compiler conservatively inserts the warning because it got expanded into
> > another
> > function, when it can't tell if it will be entirely elimintated. Can you
> > provide a code sample that demonstrates this?
> >
> >
> rte_mbuf_buf_addr() is called in rte_mbuf_data_addr_default(), both of them
> are unused by the includers of rte_mbuf.h.
>
>
> Reproduced it like this:
>
> [dmarchan@dmarchan ~]$ cat deprecated.c
> __attribute__((deprecated)) static inline void *plap(void)
> {
> return 0;
> }
>
> __attribute__((deprecated)) static inline void *plep(void)
> {
> plap();
> return 0;
> }
>
> int main(int argc, char *argv[])
> {
> return 0;
> }
> [dmarchan@dmarchan ~]$ gcc -o deprecated -Wall deprecated.c
> deprecated.c: In function ‘plep’:
> deprecated.c:8:2: warning: ‘plap’ is deprecated (declared at
> deprecated.c:1) [-Wdeprecated-declarations]
> plap();
> ^
>
Hmm, yes, that seems buggy to me. I wonder if you are seeing this bug in
action:
https://gcc.gnu.org/bugzilla//show_bug.cgi?id=80680
Seem like the behavior fits. It would be interesting to know if clang and icc
suffer from the same issue
Neil
> --
> David Marchand