[lld] r247475 - Implement -rpath.

[Hal Finkel via llvm-commits]

----- Original Message -----
> From: "Joerg Sonnenberger via llvm-commits" <llvm-commits at lists.llvm.org>
> To: "Rafael Espindola" <rafael.espindola at gmail.com>
> Cc: llvm-commits at lists.llvm.org
> Sent: Friday, September 11, 2015 5:26:44 PM
> Subject: Re: [lld] r247475 - Implement -rpath.
> 
> On Fri, Sep 11, 2015 at 09:18:57PM -0000, Rafael Espindola via
> llvm-commits wrote:
> > URL: http://llvm.org/viewvc/llvm-project?rev=247475&view=rev
> > Log:
> > Implement -rpath.
> 
> Should we really unconditionally generate RUNPATH? IMO that's a bug
> created by GNU for the semi-broken behavior of glibc's dynamic
> linker.
> This is certainly going to create problems at least for NetBSD.

What behavior do you want here?

We seem to have three choices:

 1. Generate only DT_RPATH

    At least on Linux, this overrides LD_LIBRARY_PATH

 2. Generate only DT_RUNPATH

    At least on Linux, this is searched after LD_LIBRARY_PATH

 3. Generate both DT_RPATH and DT_RUNPATH

    This is the behavior of GNU ld when -enable-new-dtags is provided, and because (at least on Linux), DT_RPATH is ignored when DT_RUNPATH is present, is equivalent to just generating DT_RUNPATH (except on pre-1999 systems which don't understand DT_RUNPATH).

In my experience, the fact that DT_RPATH overrides LD_LIBRARY_PATH is often quite inconvenient. Furthermore, as I understand it, problems with LD_LIBRARY_PATH being overridden by DT_RPATH provided the motivation for DT_RUNPATH in the first place. I can, however, see making a security argument for using DT_RPATH instead of DT_RUNPATH in limited circumstances. However, at least on Linux, use of DT_RPATH is deprecated.

Does the *BSD behavior differ here?

Another (perhaps minor) point to consider: Do we want to emulate the behavior of the old Solaris linker and leave some extra padding in the DT_RPATH field to allow slightly more freedom to edit these paths after the fact (using patchelf or similar))?

 -Hal

> 
> Joerg
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-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory