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

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Date:   Tue, 21 Jul 2020 16:52:56 +0200
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     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>,
        Nathan Chancellor <natechancellor@...il.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 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 -