[U-Boot] [PATCH v2] Makefile: adopt --std=gnu11 for HOSTCFLAGS on Linux

[Mark Kettenis]

> Date: Mon, 14 May 2018 10:57:12 -0400
> From: Tom Rini <trini at konsulko.com>
> 
> On Mon, May 14, 2018 at 04:53:49PM +0200, Mark Kettenis wrote:
> > > From: Philipp Tomsich <philipp.tomsich at theobroma-systems.com>
> > > Date: Mon, 14 May 2018 15:22:06 +0200
> > > 
> > > Following the conversion of the SPDX license tags, a number of files
> > > compiled with -pedantic now generate warnings similar to the following
> > > for using C99-style '//' comments in ISO C90 code:
> > > 
> > >   tools/gen_eth_addr.c:1:1: warning: C++ style comments are not allowed in ISO C90
> > >    // SPDX-License-Identifier: GPL-2.0+
> > >    ^
> > > 
> > > The SPDX comment-style change means that these files have adopted C99,
> > > so need to change the language-standard to --std=gnu99 or --std=gnu11
> > > to let the compiler know this.
> > > 
> > > As we now require GCC 6 or newer for the cross-compiler, the project has
> > > implicitly moved the project to GNU11: let older GCC versions on various
> > > Linux distros know to treat our host tools as GNU11 as well.
> > 
> > Note that the requirement is on the cross-compiler, not the host
> > compiler.  On our "primary" architectures OpenBSD 6.3 ships with Clang
> > 5.0.1 and the current development version uses Clang 6.0.0, which
> > default to --std=gnu11.  I do hope those will continue to be supported
> > as the host compiler...
> 
> Does Clang 5.0.1 support gnu11 ?  Note that at this point we're not even
> talking about moving to GNU11 features being used anywhere, just
> enforcing consistency between modern (post gcc-5) and old (gcc-4.x)
> compilers all in order to not have // style comments be a warning (which
> in turn is a C99/gnu99 thing).  Thanks!

Yes.  Both Clang 5.0.1 and Clang 6.0.0 support gnu11 and even default to it.

If tere is no intention to use C11 features (and frankly I don't think
C11 offers any significant benefits over C99), it'd make more sense to
add --std=gnu99 instead of --std=gnu11 wouldn't it?  That would
actually catch accidental use of C11 features.