Re: [PATCH v2] kheaders: Follow symlinks to source files.

[Yifan Hong]

On Sun, Apr 23, 2023 at 4:53 AM Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote:
>
> On Thu, Apr 20, 2023 at 10:01 AM Yifan Hong <elsk@xxxxxxxxxx> wrote:
> >
> > When the kernel is built inside a sandbox container,
> > a forest of symlinks to the source files may be
> > created in the container. In this case, the generated
> > kheaders.tar.xz should follow these symlinks
> > to access the source files, instead of packing
> > the symlinks themselves.
> >
> > Signed-off-by: Yifan Hong <elsk@xxxxxxxxxx>
> > Reviewed-by: Matthias Maennich <maennich@xxxxxxxxxx>
>
>
>
> Please teach me how to reproduce your problem.

Thanks for your reply. When I say "container", I mean a forest of
symlinks that point to the original source files. Here are the steps I
do to mimic the sandbox that the container program creates.

On an x86 machine, I have a linux tree checkout at /mnt/sdb/linux, and
an empty directory at /mnt/sdb/linux2. Then I **created this fake
sandbox** in /mnt/sdb/linux2 by doing:
```
$ cd /mnt/sdb/linux
$ find . -type d -exec mkdir -p /mnt/sdb/linux2/{} \;
$ find . -type f -exec ln -sf /mnt/sdb/linux/{} /mnt/sdb/linux2/{} \;
```

Then, I cross compile an arm64 kernel with tinyconfig. Here are the
steps I take:
```
export ARCH=arm64
export SUBARCH=arm
export CROSS_COMPILE=/home/elsk/toolchains/aarch64--glibc--stable-2022.08-1/bin/aarch64-linux-
# downloaded from https://toolchains.bootlin.com/
make tinyconfig; make menuconfig # then select CONFIG_SYSFS and CONFIG_IKHEADERS
make -j64
```

This will show that kheaders_data.tar.xz contains the symlinks, e.g. in my case:
```
$ tar tvf ./kernel/kheaders_data.tar.xz | head
[...]
lrwxrwxrwx 0/0               0 2023-04-24 11:19
./arch/arm64/include/asm/acenv.h ->
/mnt/sdb/linux/./arch/arm64/include/asm/acenv.h
```

However, the issue for me is that these symlinks are no longer useful
under sysfs when I am booting the kernel on the target arm64 machine,
because it is a different machine (arm64) than the machine (x86) where
I compiled this kernel.

>
>
>
> I built the kernel inside a container,
> but I do not see any difference.
>
>
>
> We have some symbolic links in include/,
> but those reference relative paths.
> How building the kernel in a container
> makes a difference?

Please see above; the container contains a forest of symlinks pointing
to the original source tree. Then `make` is executed in that container
directory.

>
>
> masahiro@bc5c2c958b53:/tmp/foo$ tar Jxf kheaders_data.tar.xz
> masahiro@bc5c2c958b53:/tmp/foo$ find . -type l
> ./include/dt-bindings/clock/qcom,dispcc-sm8350.h
> ./include/dt-bindings/clock/qcom,dispcc-sm8150.h
> ./include/dt-bindings/input/linux-event-codes.h
> masahiro@bc5c2c958b53:/tmp/foo$ find . -type l | xargs ls -l
> lrwxrwxrwx 1 masahiro masahiro 20 Apr 23 11:47
> ./include/dt-bindings/clock/qcom,dispcc-sm8150.h ->
> qcom,dispcc-sm8250.h
> lrwxrwxrwx 1 masahiro masahiro 20 Apr 23 11:47
> ./include/dt-bindings/clock/qcom,dispcc-sm8350.h ->
> qcom,dispcc-sm8250.h
> lrwxrwxrwx 1 masahiro masahiro 36 Apr 23 11:47
> ./include/dt-bindings/input/linux-event-codes.h ->
> ../../uapi/linux/input-event-codes.h
>
>
>
>
>
>
>
>
>
>
>
>
> > ---
> >  kernel/gen_kheaders.sh | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/gen_kheaders.sh b/kernel/gen_kheaders.sh
> > index 1ef9a87511f5..70a75a9a7535 100755
> > --- a/kernel/gen_kheaders.sh
> > +++ b/kernel/gen_kheaders.sh
> > @@ -87,7 +87,7 @@ find $cpio_dir -type f -print0 |
> >  # pre-sorted, as --sort=name might not be available.
> >  find $cpio_dir -printf "./%P\n" | LC_ALL=C sort | \
> >      tar "${KBUILD_BUILD_TIMESTAMP:+--mtime=$KBUILD_BUILD_TIMESTAMP}" \
> > -    --owner=0 --group=0 --numeric-owner --no-recursion \
> > +    --owner=0 --group=0 --numeric-owner --no-recursion --dereference \
> >      -I $XZ -cf $tarfile -C $cpio_dir/ -T - > /dev/null
> >
> >  echo $headers_md5 > kernel/kheaders.md5
> > --
> > 2.40.0.634.g4ca3ef3211-goog
> >
>
>
> --
> Best Regards
> Masahiro Yamada
>
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