[Bug libc/30306] New: ld.so.conf could easily / should support binary specific LD_PATH directory search path settings ?

[Bug libc/30306] New: ld.so.conf could easily / should support binary specific LD_PATH directory search path settings ?

[jason.vas.dias at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=30306

            Bug ID: 30306
           Summary: ld.so.conf could easily / should support binary
                    specific LD_PATH directory search path settings ?
           Product: glibc
           Version: unspecified
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: jason.vas.dias at gmail dot com
                CC: drepper.fsp at gmail dot com
  Target Milestone: ---

I am considering developing a patch to ld.so's ld.so.conf handling 
that , as well as supporting DIRECTORY lists to add to the effective
LD_PATH ($LD_LIBRARY_PATH), could easily also support a new syntax like:

/usr/bin/perf:+/usr/local/lib64

to create an EXCEPTION for the /usr/bin/perf program,
so that for the specific binary file /usr/bin/perf,  
/usr/local/lib64 would be added to the 
"effective $LD_LIBRARY_PATH" := LD_PATH 
(my shorthand).

Perhaps an alternative on platforms which support filesystems
with extended attributes would be to support files having
a 'LD_SO_PATH:' Extended Attribute, which ld.so could support
with some new

/${DIRECTORY}/:EA_LD_SO_PATH:true

setting to enable EA LD_SO_PATH checking for all files under 
${DIRECTORY} .

This is to solve this problem:
 https://bugzilla.redhat.com/show_bug.cgi?id=2183758
where the linux kernel 'perf' package from v6.2.8 cannot build
without the libbpf 0.8.0+ packages, but only v0.7.0 packages
come with FC36, so I need to build libbpf-1.1.0-2 into /usr/local/,
so it installs its libraries into /usr/local/lib64, then I DO build
perf with the ld / gcc '-R /usr/local/lib64' option, but this is 
conscientiously stripped out of LDFLAGS / from resultant binaries,
I don't want to have to patch the binary, so I have to replace
/usr/bin/perf with a script : 
'
!#/bin/bash
exec /usr/bin/perf.bin "$@"
', which is not ideal.

I think ld.so could provide a most elegant, simple & efficient
solution to this problem with support for a tiny extra bit of new
configuration syntax - I'd like my ld.so to provide this!

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[Bug libc/30306] ld.so.conf could easily / should support binary specific LD_PATH directory search path settings ?

[jason.vas.dias at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=30306

--- Comment #1 from Jason Vas Dias <jason.vas.dias at gmail dot com> ---
Oops, of course my /usr/bin/perf script has to be:
'
!#/bin/bash
declare -x LD_LIBRARY_PATH=/usr/local/lib64
exec /usr/bin/perf.bin "$@"
',

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[Bug libc/30306] ld.so.conf could easily / should support binary specific LD_PATH directory search path settings ?

[schwab@linux-m68k.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30306

--- Comment #2 from Andreas Schwab <schwab@linux-m68k.org> ---
Why can't you just add /usr/local/lib64 unconditionally to /etc/ld.so.conf?

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[Bug libc/30306] ld.so.conf could easily / should support binary specific LD_PATH directory search path settings ?

[jason.vas.dias at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=30306

--- Comment #3 from Jason Vas Dias <jason.vas.dias at gmail dot com> ---
RE: Comment #2: 
> Why can't you just add /usr/local/lib64 unconditionally to /etc/ld.so.conf?

Thanks, Andreas - 

Because there may be many other libraries in /usr/local/lib64 - in fact,
there is a libgcc-shared.so and a libstdc++.so.6 in /usr/local/lib64,
which I'd rather not pick up at all - I want to be able to move
libbpf's libraries to some /usr/local/libbpf-v1.1.0/lib64 directory ,
and specify that they apply ONLY to links needed for /usr/bin/perf,
I do NOT want these updated libbpf* links to update the system
libbpf at all, which MUST remain at v0.7.0, else everything that
uses libbpf (except perf) will break .

It just seems to me that having some very simple extra config
in ld.so.conf, to apply a LD_PATH only to certain executables,
would prevent a whole host of error prone disasters involved 
with binary patching in of a DT_RUNPATH ELF note .

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[Bug libc/30306] ld.so.conf could easily / should support binary specific LD_PATH directory search path settings ?

[adhemerval.zanella at linaro dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30306

Adhemerval Zanella <adhemerval.zanella at linaro dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |adhemerval.zanella at linaro dot o
                   |                            |rg

--- Comment #4 from Adhemerval Zanella <adhemerval.zanella at linaro dot org> ---
(In reply to Jason Vas Dias from comment #3)
> RE: Comment #2: 
> > Why can't you just add /usr/local/lib64 unconditionally to /etc/ld.so.conf?
> 
> Thanks, Andreas - 
> 
> Because there may be many other libraries in /usr/local/lib64 - in fact,
> there is a libgcc-shared.so and a libstdc++.so.6 in /usr/local/lib64,
> which I'd rather not pick up at all - I want to be able to move
> libbpf's libraries to some /usr/local/libbpf-v1.1.0/lib64 directory ,
> and specify that they apply ONLY to links needed for /usr/bin/perf,
> I do NOT want these updated libbpf* links to update the system
> libbpf at all, which MUST remain at v0.7.0, else everything that
> uses libbpf (except perf) will break .
> 
> It just seems to me that having some very simple extra config
> in ld.so.conf, to apply a LD_PATH only to certain executables,
> would prevent a whole host of error prone disasters involved 
> with binary patching in of a DT_RUNPATH ELF note .

We already have RPATH, which has precedence over the loader cache and it is not
subject to DF_1_NODEFLIB.  RPATH also accepts $ORIGIN, which does not tie where
the binary is installed; and it is also simpler to use since do not need admin
credential (to update ld.so.config and run ldconfig).

I don't have a strong opinion, but this seems to just replicate a subset of
RPATH and it will add an extra complexity on loader cache (which will need to
keep track of whether the entry has a path associated, and add a new type to
handle the directory suggestion).  

It also adds some corner cases: 

  - should it just support ET_EXEC? 
  - For ET_DYN, should it tie to the filesystem name or with its SONAME? 
  - The LD_LIBRARY_PATH is handled earlier than the cache and it is not subject
to DF_1_NODEFLIB, however your suggestion ties with LD_LIBRARY_PATH.

So I am not sure if this will be really an improvement.

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