[Buildroot] [PATCH next v6 07/10] core: implement per-package SDK and target

[Thomas Petazzoni <thomas.petazzoni@bootlin.com>]

Hello,

Arnout, Yann, see below some discussion where your input might be
useful.

On Thu, 6 Dec 2018 11:21:25 +0100, Andreas Naumann wrote:

> Just to make sure I just did the above using your ppsh-v6 branch with 
> the wandboard_defconfig. The only additional change was to use the 
> external linaro toolchain. After 'make'
>    $ readelf -d output/host/sbin/mkfs.ext3
> shows
>    0x000000000000001d (RUNPATH)            Bibliothek runpath: 
> [/local/gsrc/buildroot.upstream/output/per-package/host-e2fsprogs/host/lib]
> 
> which is already unexpected, shouldn't it show .../output/host/lib?
> After 'make prepare-sdk'
>    $ readelf -d output/host/sbin/mkfs.ext3
> shows
>    0x000000000000001d (RUNPATH)            Bibliothek runpath: []

OK, so I investigated this issue, and now I understand where it comes
from, but I'm not yet sure how to fix it properly.

Basically, *without* per-package directory enabled, the RPATH of
binaries looks like this:

  Library rpath: [/home/thomas/projets/buildroot/output/host/lib]

then, support/scripts/fix-rpath calls patchelf with the following
invocation:

  /home/thomas/projets/buildroot/output/host/bin/patchelf --make-rpath-relative /home/thomas/projets/buildroot/output/host --relative-to-file /home/thomas/projets/buildroot/output/host/sbin/mke2fs

This works fine, and causes the resulting binary to have the following
RPATH:

  Library runpath: [$ORIGIN/../lib]

You can see that the original "Library rpath", which
is /home/thomas/projets/buildroot/output/host/lib is located *inside*
the ROOTDIR passed as the --make-rpath-relative
option: /home/thomas/projets/buildroot/output/host.

Now, with per-package directory enabled, the RPATH of binaries when
building looks like this:

  Library rpath: [/home/thomas/projets/buildroot/output/per-package/host-e2fsprogs/host/lib]

So it is no longer within the ROOTDIR passed as patchelf's
--make-rpath-relative argument.

The logic used by patchelf is explained in
package/patchelf/0003-Add-option-to-make-the-rpath-relative-under-a-specif.patch:

====

RPATHDIR starts with "$ORIGIN":
    The original build-system already took care of setting a relative
    RPATH, resolve it and test if it's valid (does exist)

RPATHDIR starts with ROOTDIR:
    The original build-system added some absolute RPATH (absolute on
    the build machine). Test if it's valid (does exist).

ROOTDIR/RPATHDIR exists:
    The original build-system already took care of setting an absolute
    RPATH (absolute in the final rootfs), resolve it and test if it's
    valid (does exist).

RPATHDIR points somewhere else:
    (can be anywhere: build trees, staging tree, host location,
    non-existing location, etc.). Just discard such a path.

====

So, without per-package directory, we fall in case (2) above.

With per-package directory, we fall in case (4) above, and therefore
the RPATH is discarded.

At this point, I am not sure at which level and how the issue should be
fixed. Needs some thought. Input/ideas welcome.

Best regards,

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com