linux-kernel - Re: [PATCH v2 3/5] kbuild: Use relative path for $(objtree)

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Date:   Mon, 16 Oct 2017 12:26:18 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Michal Marek <mmarek@...e.cz>
Cc:     Richard Weinberger <richard.weinberger@...il.com>,
        linux-kbuild <linux-kbuild@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Sam Ravnborg <sam@...nborg.org>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v2 3/5] kbuild: Use relative path for $(objtree)

Hi Michal,

On Thu, Jun 5, 2014 at 5:56 PM, Michal Marek <mmarek@...e.cz> wrote:
> On Wed, Jun 04, 2014 at 03:12:33PM +0200, Michal Marek wrote:
>> On 2014-06-04 11:43, Michal Marek wrote:
>> > On 2014-06-04 11:03, Richard Weinberger wrote:
>> >> To reproduce run:
>> >> make defconfig ARCH=um O=/mnt/o && make linux ARCH=um O=/mnt/
>> >>
>> >> If there is anything in UML which needs fixing, please tell. :-)
>> >
>> > I'll have a look, thanks for the report.
>>
>> Findings so far: For some reason, syscalls_32.h is generated in the
>> source tree (which is wrong) and syscalls_64.h is not generated at all.
>> Looking further.
>
> Can you try the below patch? The same pattern is used in the rules for
> tools/ and tools/% in the main Makefile, need to look into that as well.
> But UML should work now.
>
> Michal
>
> From d4bc590f8716f7dde6b7bca319097ac30a8cb0b4 Mon Sep 17 00:00:00 2001
> From: Michal Marek <mmarek@...e.cz>
> Date: Thu, 5 Jun 2014 17:44:44 +0200
> Subject: [PATCH] um: Fix for relative objtree when generating x86 headers
>
> In an O= build, rely on the generated Makefile to call the main Makefile
> properly. When building in the source tree, we do not need to specify
> the -C and O= either. This fixes the problem when $(objtree) is a
> relative path and the -C changes the directory.
>
> Reported-by: Richard Weinberger <richard.weinberger@...il.com>
> Signed-off-by: Michal Marek <mmarek@...e.cz>
> ---
>  arch/um/Makefile | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/arch/um/Makefile b/arch/um/Makefile
> index 36e658a..e4b1a96 100644
> --- a/arch/um/Makefile
> +++ b/arch/um/Makefile
> @@ -111,8 +111,7 @@ endef
>  KBUILD_KCONFIG := $(HOST_DIR)/um/Kconfig
>
>  archheaders:
> -       $(Q)$(MAKE) -C '$(srctree)' KBUILD_SRC= \
> -               ARCH=$(HEADER_ARCH) O='$(objtree)' archheaders
> +       $(Q)$(MAKE) KBUILD_SRC= ARCH=$(HEADER_ARCH) archheaders
>
>  archprepare: include/generated/user_constants.h

This now commit d4bc590f8716f7dd ("um: Fix for relative objtree when
generating x86 headers").

When using O=, the build enters an infinite loop on v4.14-rc5.
With V=1:

    make KBUILD_SRC= ARCH=x86 archheaders
    make -C /scratch/geert/linux/linux
O=/scratch/geert/build/linux-uml-amd64/. archheaders
    make -C /scratch/geert/build/linux-uml-amd64
KBUILD_SRC=/scratch/geert/linux/linux \
    -f /scratch/geert/linux/linux/Makefile archheaders
    make KBUILD_SRC= ARCH=x86 archheaders
    make -C /scratch/geert/linux/linux
O=/scratch/geert/build/linux-uml-amd64/. archheaders
    make -C /scratch/geert/build/linux-uml-amd64
KBUILD_SRC=/scratch/geert/linux/linux \
    -f /scratch/geert/linux/linux/Makefile archheaders
    ...

As it's been a (long) while I buily UML, I started a bisect, which pointed to
the commit above.
The problem actually already happened on commit d4bc590f8716f7dd, so this
has been broken since v3.16:

    make KBUILD_SRC= ARCH=x86 archheaders
    make -C /scratch/geert/linux/linux
O=/scratch/geert/build/linux-uml-amd64/. archheaders
    make -C /scratch/geert/build/linux-uml-amd64 \
    KBUILD_SRC=/scratch/geert/linux/linux \
    KBUILD_EXTMOD="" -f /scratch/geert/linux/linux/Makefile \
    archheaders
    make KBUILD_SRC= ARCH=x86 archheaders
    make -C /scratch/geert/linux/linux
O=/scratch/geert/build/linux-uml-amd64/. archheaders
    make -C /scratch/geert/build/linux-uml-amd64 \
    KBUILD_SRC=/scratch/geert/linux/linux \
    KBUILD_EXTMOD="" -f /scratch/geert/linux/linux/Makefile \
    archheaders
    ...

Unfortunately reverting that commit doesn't help, as that causes the
failure that
commit was supposed to fix:

    /scratch/geert/linux/linux/arch/x86/um/user-offsets.c:19:29: fatal
error: asm/syscalls_64.h: No such file or directory
     #include <asm/syscalls_64.h>
                                 ^
    compilation terminated.
    /scratch/geert/linux/linux/scripts/Makefile.build:154: recipe for
target 'arch/x86/um/user-offsets.s' failed

Do you have any clue? Thanks!

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds