[cfe-dev] [RFC] Prefer libraries installed next to Clang over those from GCC

[Hahnfeld, Jonas via cfe-dev]

Hi Hal,



Thanks for the idea: I will adapt the patch to introduce a new CMake flag and 
to not change the default behavior.



Thanks,

Jonas



From: Hal Finkel [mailto:hfinkel at anl.gov]
Sent: Monday, January 30, 2017 5:58 PM
To: Hahnfeld, Jonas; cfe-dev at lists.llvm.org
Subject: Re: [cfe-dev] [RFC] Prefer libraries installed next to Clang over 
those from GCC





On 01/30/2017 09:09 AM, Hahnfeld, Jonas via cfe-dev wrote:

Hi,

Background: I'm on CentOS 7 which has GCC 4.8 installed in /usr/bin and I'm
installing Clang to, let's say, /opt/clang. (I'm doing so with
CLANG_DEFAULT_CXX_STDLIB=libc++, just if you wonder why the following
matters to me...)
With the current behavior, -lunwind passed to Clang will pull in the system
default non-GNU /usr/lib/libunwind.so.8. IMO it should take LLVM's version
in /opt/clang/lib/libunwind.so.1

That's why I would like to change the default order for searching libraries
in Clang. Currently (and most probably due to historical reasons), the
Driver adds paths next to GCC first.
I propose to prefer paths next to the installed Clang. You can find the
patch doing the change here: https://reviews.llvm.org/D26244

However, this has a potential impact as Chandler pointed out in above patch
if Clang is installed to /opt/software together with other software.
With my proposed change, Clang will link against
/opt/software/lib/libunrelated.so when passed -lunrelated whereas before it
had preferred /usr/lib/libunrelated.so (assuming that the library exists in
both places).
Is that considered an important scenario or can we expect our users to
install Clang separately?

Any other feedback on that topic?


I think this is an important usage scenario, but because of the complication 
Chandler mentioned, I don't think we can enable it by default. I think it is 
very reasonable to have some CMake flag that enables this behavior.

 -Hal





Jonas

--
Jonas Hahnfeld, MATSE-Auszubildender

IT Center
Group: High Performance Computing
Division: Computational Science and Engineering
RWTH Aachen University
Seffenter Weg 23
D 52074  Aachen (Germany)
Hahnfeld at itc.rwth-aachen.de
www.itc.rwth-aachen.de








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-- 
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory
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