Re: [PATCH] compiler-gcc: get back Clang build
From: Joe Perches
Date: Tue Aug 21 2018 - 13:22:52 EST
On Tue, 2018-08-21 at 09:57 -0700, Nick Desaulniers wrote:
> On Tue, Aug 21, 2018 at 9:33 AM Joe Perches <joe@xxxxxxxxxxx> wrote:
> > On Tue, 2018-08-21 at 15:48 +0900, Masahiro Yamada wrote:
> > > Commit cafa0010cd51 ("Raise the minimum required gcc version to 4.6")
> > > missed the fact that <linux/compiler-gcc.h> is included by Clang
> > > as well as by GCC.
> > >
> > > Clang actually defines __GNUC__, __GNUC_MINOR__, __GNUC_PATCHLEVEL__
> > > and it looks like GCC 4.2.1.
> > >
> > > $ scripts/gcc-version.sh -p clang
> > > 040201
> > >
> > > If you try to build the kernel with Clang, you will get the
> > > "Sorry, your compiler is too old - please upgrade it."
> > > followed by a bunch of "unknown attribute" warnings.
> > >
> > > Add !defined(__clang__) to the minimum version check.
> > >
> > > Also, revive the version test blocks for versions >= 4.2.1
> > > in order to disable features not supported by Clang.
> > What is the minimum clang version required to compile the kernel?
> Depends on the architecture and which kernel version/LTS branch you're
> using. I'm trying to backport fixes to LTS branches, but sometimes a
> compiler upgrade is required. I know that's not great, but I'm
> actively trying to fix it.
Can you enumerate these dependencies please.
> > What features are not supported by the minimum clang version?
And enumerate this too please.
Uglifying the compiler-gcc file to support
clang features that can be overridden in
compiler-clang.h instead is not a good way
to fix compilation for clang.
But still, whatever features in the various
clang versions that need accommodation also
need listing out in compiler-clang.h, not in
> $ git describe --contains e501ce9 | sed 's/~.*//'
Thanks, but I know this.
The question remains, if clang can't compile
v4.17, why does it immediately matter for v4.19?
Why wouldn't overriding the clang __GNUC_<foo>
#defines in compiler-gcc.h work acceptably with
adding whatever is necessary to compiler-clang.h?
I'll experiment with a compiler-clang.h patch.