linux-kernel - Re: [PATCH v2] Makefile: Fix GCC_TOOLCHAIN_DIR prefix for Clang cross compilation

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Date:   Tue, 21 Jul 2020 10:13:23 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Sedat Dilek <sedat.dilek@...il.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Fangrui Song <maskray@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Clang-Built-Linux ML <clang-built-linux@...glegroups.com>,
        stable@...r.kernel.org, Jian Cai <jiancai@...gle.com>,
        Bill Wendling <morbo@...gle.com>,
        Manoj Gupta <manojgupta@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH v2] Makefile: Fix GCC_TOOLCHAIN_DIR prefix for Clang
 cross compilation

On Tue, Jul 21, 2020 at 04:52:56PM +0200, Sedat Dilek wrote:
> On Tue, Jul 21, 2020 at 12:40 PM Greg KH <gregkh@...uxfoundation.org> wrote:
> >
> > On Mon, Jul 20, 2020 at 09:19:38PM -0700, Fangrui Song wrote:
> > > When CROSS_COMPILE is set (e.g. aarch64-linux-gnu-), if
> > > $(CROSS_COMPILE)elfedit is found at /usr/bin/aarch64-linux-gnu-elfedit,
> > > GCC_TOOLCHAIN_DIR will be set to /usr/bin/.  --prefix= will be set to
> > > /usr/bin/ and Clang as of 11 will search for both
> > > $(prefix)aarch64-linux-gnu-$needle and $(prefix)$needle.
> > >
> > > GCC searchs for $(prefix)aarch64-linux-gnu/$version/$needle,
> > > $(prefix)aarch64-linux-gnu/$needle and $(prefix)$needle. In practice,
> > > $(prefix)aarch64-linux-gnu/$needle rarely contains executables.
> > >
> > > To better model how GCC's -B/--prefix takes in effect in practice, newer
> > > Clang (since
> > > https://github.com/llvm/llvm-project/commit/3452a0d8c17f7166f479706b293caf6ac76ffd90)
> > > only searches for $(prefix)$needle. Currently it will find /usr/bin/as
> > > instead of /usr/bin/aarch64-linux-gnu-as.
> > >
> > > Set --prefix= to $(GCC_TOOLCHAIN_DIR)$(CROSS_COMPILE)
> > > (/usr/bin/aarch64-linux-gnu-) so that newer Clang can find the
> > > appropriate cross compiling GNU as (when -no-integrated-as is in
> > > effect).
> > >
> > > Reported-by: Nathan Chancellor <natechancellor@...il.com>
> > > Signed-off-by: Fangrui Song <maskray@...gle.com>
> > > Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
> > > Tested-by: Nathan Chancellor <natechancellor@...il.com>
> > > Tested-by: Nick Desaulniers <ndesaulniers@...gle.com>
> > > Link: https://github.com/ClangBuiltLinux/linux/issues/1099
> > > ---
> > > Changes in v2:
> > > * Updated description to add tags and the llvm-project commit link.
> > > * Fixed a typo.
> >
> >
> > <formletter>
> >
> > This is not the correct way to submit patches for inclusion in the
> > stable kernel tree.  Please read:
> >     https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
> > for how to do this properly.
> >
> > </formletter>
> >
> 
> Hi Fangrui,
> 
> your patch needs to be accepted first in Linus tree - among other
> things to have a unique commit-id for inclusion into any affected
> Linux-stable trees.
> 
> Regards,
> - Sedat -

You are not wrong but that is not what Greg's auto response is complaining
about. It is that stable@...r.kernel.org was cc'd but there was no

Cc: stable@...r.kernel.org

in the commit message, which is how patches get automatically picked up
by Greg and Sasha once they hit Linus's tree.

That line should be added above my Reported-by tag. Fangrui, sorry for
not being clear in my initial response :(

Cheers,
Nathan