[Bug testsuite/79867] New: [cygwin] LD_LIBRARY_PATH ignored, contaminating (nearly?) all test results

["daniel.santos at pobox dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79867

            Bug ID: 79867
           Summary: [cygwin] LD_LIBRARY_PATH ignored, contaminating
                    (nearly?) all test results
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: testsuite
          Assignee: unassigned at gcc dot gnu.org
          Reporter: daniel.santos at pobox dot com
  Target Milestone: ---

Running the testsuite resulted in 15,308 instances of the error message
"cyggfortran-4.dll: cannot open shared object file: No such file or directory"
(similar for libatomic).  I could see in the log file that LD_LIBRARY_PATH was
set correctly and that the file did exist in that path.  After much
experimentation, wailing, gnashing of teeth and a few emails to the Cygwin list
(https://cygwin.com/ml/cygwin/2017-03/msg00059.html) I learned that
LD_LIBRARY_PATH is *not* used in Cygwin.  (I presume because there's no
practical way to get the Windows kernel to use it when loading libraries.)  I
couldn't even debug it with gdb because the link failure happened before the
image's entry point was even called.

This means that when we run the testsuite on Cygwin and we're expecting to test
using what we have built, but are actually linking in libgcc, libgfortran,
libstdc++, etc. from the environment and NOT from the build tree, so that any
Cygwin-specific regression in those libraries that arise between a.) the
release that is installed and b.) the version being tested will not be exposed
by any normal execution of the testsuite.

I'm still fairly green with DejaGnu and Tcl/expect, but perhaps the solution is
to

1. Add a platform-abstracted mechanism to DejaGnu for altering the executable
and library search paths, and
2. Deprecate and replace all usage (reading or modifying) of the
LD_LIBRARY_PATH, SHLIB_PATH and PATH environment variables in tests.

Then on Cygwin, DejaGnu can internally track the executable and library search
paths separately as they are modified and set the PATH environment variable
accordingly.

It would also be nice to have an interim hack for running tests on Cygwin.