[dpdk-dev] [PATCH] eal: remove variable length array
Jeff Shaw
jeffrey.b.shaw at intel.com
Fri Dec 14 20:17:06 CET 2018
On Fri, Dec 14, 2018 at 10:59:28AM -0800, Jeff Shaw wrote:
> On Fri, Dec 14, 2018 at 10:36:03AM -0800, Stephen Hemminger wrote:
> > On Fri, 14 Dec 2018 08:38:27 -0800
> > Jeff Shaw <jeffrey.b.shaw at intel.com> wrote:
> >
> > > Compilers that do not support the C11 standard, or do not implement
> > > gcc extensions, may not support variable length arrays.
> > >
> > > The code prior to this commit produced the following warning when
> > > compiled with "-Wvla -std=c90".
> > >
> > > warning: ISO C90 forbids variable length array ‘array’ [-Wvla]
> > >
> > > This commit removes the variable length array from the PMD debug
> > > trace function by allocating memory dynamically on the stack using
> > > alloca().
> > >
> > > Signed-off-by: Jeff Shaw <jeffrey.b.shaw at intel.com>
> > > ---
> > > lib/librte_eal/common/include/rte_dev.h | 19 +++++++++----------
> > > 1 file changed, 9 insertions(+), 10 deletions(-)
> > >
> > > diff --git a/lib/librte_eal/common/include/rte_dev.h b/lib/librte_eal/common/include/rte_dev.h
> > > index a9724dc91..af772872b 100644
> > > --- a/lib/librte_eal/common/include/rte_dev.h
> > > +++ b/lib/librte_eal/common/include/rte_dev.h
> > > @@ -47,22 +47,21 @@ __attribute__((format(printf, 2, 0)))
> > > static inline void
> > > rte_pmd_debug_trace(const char *func_name, const char *fmt, ...)
> > > {
> > > + char *buffer;
> > > + int buf_len;
> > > va_list ap;
> > >
> > > va_start(ap, fmt);
> > > + buf_len = vsnprintf(NULL, 0, fmt, ap) + 1;
> > > + va_end(ap);
> > >
> > > - {
> > > - char buffer[vsnprintf(NULL, 0, fmt, ap) + 1];
> > > + buffer = (char *)alloca(buf_len);
> >
> > alloca is void * so cast is not necessary.
>
> I get a compiler warning on Windows, hence the cast. I suppose we could
> disable the warning.
>
> >
> > You might be able to skip the buffering step entirely by using rte_log
> > a little more creatively, see how other logging works.
>
> Probably right... this eventuall needs to be done in ~100 other places,
> most of which aren't used with rte_log(), so it seemed fitting.
>
> >
> > But to go further since rte_pmd_debug_trace is not used anywhere in
> > current code base in DPDK, it should just be removed.
>
> Much better solution :)
Actually, it cannot be removed. It is used by librte_eventdev. When
RTE_LIBRTE_EVENTDEV_DEBUG is defined, the RTE_PMD_DEBUG_TRACE macro
uses rte_pmd_debug_trace.
I will remove the cast and update the commit message to reference C99
instead of C11 as requested by Mattias R.
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