[Buildroot] [RFC PATCH v3 00/10] Make the SDK relocatable

[Wolfgang Grandegger <wg@grandegger.com>]

Am 28.06.2017 um 12:41 schrieb Arnout Vandecappelle:
> 
> 
> On 28-06-17 08:45, Wolfgang Grandegger wrote:
>> Am 28.06.2017 um 00:47 schrieb Arnout Vandecappelle:
>>>
>>>
>>> On 22-06-17 08:37, Wolfgang Grandegger wrote:
>>>> Hello Arnout,
>>>>
>>>> Am 21.06.2017 um 23:03 schrieb Arnout Vandecappelle:
>>>>>     Hi Wolfgang,
>>>>>
>>>>> On 21-06-17 09:59, Wolfgang Grandegger wrote:
>>>>>> Hello,
>>>>>>
>>>>>> this topic is still pending... some more input below...
>>>>>>
>>>>>> Am 27.04.2017 um 11:37 schrieb Wolfgang Grandegger:
>>>>>>> Hello Arnout,
>>>>>>>
>>>>>>> Am 12.04.2017 um 15:59 schrieb Arnout Vandecappelle:
>>>>>>>>
>>>>>>>>
>>>>>>>> On 23-03-17 08:54, Wolfgang Grandegger wrote:
> [snip]
>>>>>>>>     I'm not entirely sure about staging, whether ld will use RPATH as an
>>>>>>>> alternative to -L and in that case whether it is done relative to sysroot or
>>>>>>>> not.
>>>>>>>
>>>>>>> So far, the patch series works for me very well. Just my usecase, of course.
>>>>>
>>>>>     IIRC I checked a while ago and it looked like ld would use RPATH as a
>>>>> link path
>>>>> (i.e. as if it's given with -L), and I think it was NOT relative to sysroot.
>>>>> Which means that we shouldn't make the RPATHs in staging relative to
>>>>> STAGING_DIR, otherwise it may pick up the library from the host. This really
>>>>> shouldn't happen because the link normally should get the appropriate -L
>>>>> flag to
>>>>> find the target lib and the -L has precedence over RPATH, but better be safe.
>>>>
>>>> The man page of "ld" says:
>>>>
>>>> "The linker uses the following search paths to locate required shared libraries:
>>>>    ...
>>>>    6.  For a native ELF linker, the directories in "DT_RUNPATH" or "DT_RPATH"
>>>> of a shared library are
>>>>        searched for shared libraries needed by it. The "DT_RPATH" entries are
>>>> ignored if "DT_RUNPATH" entries
>>>>        exist."
>>>
>>>    But this doesn't clarify if these paths are interpreted relative to --sysroot
>>> or not.
>>
>> I'm going to check what is in the orogilan rpath. I guess that the pathes are
>> absolute to the host.
> 
>   Thinking again about this: for staging, we should probably remove RPATH completely.
> 
> * At build time, the RPATH is only used as an extra directory to search for
> shared library. However, any such directory should anyway be passed with -L to
> cover the static libs case. So it's better to remove the RPATH, then we see any
> missing -L earlier.
> 
> * The binaries in staging should never be executed. They shouldn't be copied to
> target any more. Therefore, the RPATH is never used by the dynamic linker.
> 
>   So to keep things simple and to avoid discussion about the --sysroot, I propose
> to remove RPATH entirely.
> 
>>
>>>>
>>>> Then we should use $ORIGIN relative to the ELF file for the staging tree
>>>> (like for the host tree) to make it relocatable.
>>>
>>>    That is for sure the safest option.
>>
>> BTW, like for the target, /lib and /usr/lib is removed from the rpath. Don't
>> know if the linker looks into sysrot/lib or sysroot/usr/lib by default.
>>
>>> [snip]
>>>>>>>>> Things not yet addressed:
>>>>>>>>>
>>>>>>>>> - "make toolchain" creates a toolchain tree which still has references
>>>>>>>>>      to the build system (in ELF and text files).
>>>>>>>>
>>>>>>>>     A solution to this (and other problems) is to use the same approach as
>>>>>>>> check-bin-arch: do it as an instrumentation hook for each package, and
>>>>>>>> only look
>>>>>>>> at the files added by that package. That way, the overhead is spread out
>>>>>>>> over
>>>>>>>> the entire build process, and doing rebuilds doesn't run patchelf on all
>>>>>>>> files
>>>>>>>> anymore in the finalize step.
>>>>>>>
>>>>>>> This is just to solve the issue mentioned above or a general approach
>>>>>>> (instead
>>>>>>> of doning rtpath sanitation at the end)?
>>>>>>
>>>>>> Any opinions here?
>>>>>
>>>>>     Preferably as an instrumentation hook, because:
>>>>> - it speeds things up dramatically if you do 'make foo-rebuild';
>>>>> - things are still correct if you interrupt the build in the middle;
>>>>> - it makes no difference if you do a rebuild (if patchelf is done at the end,
>>>>> and then you rebuild a package, the RPATH in the libs you link with is
>>>>> different
>>>>> than the first time you built it).
>>>>
>>>> OK, as I see it, check-bin-arch is only for the files in the target tree.
>>>> Having a
>>>> closer look now.
>>>
>>>    Yes, for this approach to work the packages-file-list has to be extended to
>>> cover host and staging as well. And since host includes staging, the find
>>> command for host is a little complicated.
>>
>> With that approach we do not need "find" any longer. There will by a list of
>> installed files per package.
> 
>   There is currently no packages-file-list for host and staging, so you need to
> build it. To build the list, you need to do a find.

The list is built with "comm -13 ...". While implementing that way, I 
realized that I need patchelf for the host as very first package. Any 
idea how that could achieved?

Wolfgang.