[dpdk-dev] [PATCH 01/10] mk: adjust gcc flags for new gcc 7 warnings

[Bruce Richardson]

On Fri, May 05, 2017 at 12:02:44PM +0200, Thomas Monjalon wrote:
> In this series, there are some fixes for fall-through comments,
> missing break and missing initializers.
> I think there is no discussion about accepting them in 17.05.
> The last item to discuss it the new snprintf warning:
> 
> 05/05/2017 11:42, Bruce Richardson:
> > On Thu, May 04, 2017 at 09:38:08AM -0700, Stephen Hemminger wrote:
> > > On Thu,  4 May 2017 16:38:13 +0100
> > > Bruce Richardson <bruce.richardson at intel.com> wrote:
> > > > 2. GCC also warns about an snprintf where there may be truncation and the
> > > > return value is not checked. Given that we often use snprintf in DPDK in
> > > > place of strncpy, and in many cases where truncation is not a problem, we
> > > > can just disable this particular warning.
> [...]
> > > > --- a/mk/toolchain/gcc/rte.vars.mk
> > > > +++ b/mk/toolchain/gcc/rte.vars.mk
> > > > +# Ignore errors for snprintf truncation
> > > > +WERROR_FLAGS += -Wno-format-truncation
> [...]
> > 2. for the format truncation warning, ideally, yes we should fix the
> > code, except that I don't believe this is feasible in the short term,
> > and I also don't believe it is desirable. We extensively use snprintf
> > because it has sane/safe truncation, and in many cases we don't care if
> > it is being truncated. Therefore disabling the warning seems the best
> > approach to me. Furthermore, if we want 17.05 to compile with GCC 7,
> > this is the best option within that timeframe.
> 
> We could imagine an explicit ignore of the return code.
> However, do we really want this new coding rule for every snprintf?
> It is a common call in DPDK:
> 	git grep '\<snprintf\>' | wc -l
> 	774
> And probably almost never checked:
> 	git grep '^[[:space:]]*\<snprintf\>' | wc -l
> 	660
> 
> I suggest to disable this new warning in GCC 7.
> Any opinions?

I'd suggest that even fewer than that are actually recorded, let alone
checked:

git grep '= *snprintf\>' | wc -l
89

So I'm (obviously) +1 for dropping this warning check.

/Bruce