[GHC] #10955: GHC on windows does not resolve DLL dependencies

[GHC]

#10955: GHC on windows does not resolve DLL dependencies
-------------------------------------+-------------------------------------
        Reporter:  Phyx-             |                Owner:  Phyx-
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Runtime System    |              Version:  7.10.2
  (Linker)                           |
      Resolution:                    |             Keywords:
Operating System:  Windows           |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Runtime crash     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1340
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by Tamar Christina <tamar@…>):

 In [changeset:"6e6438e15f33cb94ad6338e950e693f59d046385/ghc"
 6e6438e1/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="6e6438e15f33cb94ad6338e950e693f59d046385"
 Allow the GHCi Linker to resolve related dependencies when loading DLLs

 Summary:
 GHCi does not correctly tell the Windows Loader how to handle dependencies
 to DLL's
 that are not on the standard Windows load path:

 1. The directory from which the application loaded.
 2. The current directory.
 3. The system directory. Use the GetSystemDirectory function to get the
 path of this directory.
 4. The 16-bit system directory. There is no function that obtains the path
 of this directory,
    but it is searched.
 5. The Windows directory. Use the GetWindowsDirectory function to get the
 path of this directory.
 6. The directories that are listed in the PATH environment variable.
    Note that this does not include the per-application path specified by
 the
    AppPaths registry key. The App Paths key is not used when computing the
 DLL search path.

 So what this means is given two DLLs `A` and `B` and `B` depending on `A`.
 If we put both DLLs into a new folder bin and then call GHC with:

 `ghc -L$(PWD)/bin -lB`

 the loading will fail as the Windows loader will try to load the
 dependency of `B` and fail
 since it cannot find `A`.

 *IMPORTANT* this patch drops XP Support.
 The  APIs being used were natively added to Windows 8+ and backported to
 Windows 7 and Vista
 via a mandatory security patch (in 2011). This means that there is a
 chance that KB2533623 has
 not been installed on certain machines. For those machines I display a
 warning and
 temporarily expand the `PATH` to allow it to load.

 This patch will make sure that paths provided by the user with `-L` *and*
 the folder in which a
 DLL is found are added to the search path. It does so using one of two
 methods depending upon how
 new of a Windows version we are running on:

 - If the APIs are available it will use `addDllDirectory` and
 `removeDllDirectory`.
    The order of which these directories are searched is nondeterministic.
 - If the APIs are not available it means that we're running on a pretty
 old unpatched machine.
   But if it's being used in an environment with no internet access it may
 be the case.
   So if the APIs are not available we temporarily extend the `PATH` with
 the directories.
   A warning is also displayed to the user informing them that the linking
 may fail,
   and if it does, install the needed patch. The `PATH` variable has
 limitations.

 Test Plan:
 ./validate

 Added two new test T10955 and T10955dyn

 Reviewers: erikd, bgamari, thomie, hvr, austin

 Reviewed By: erikd, thomie

 Subscribers: #ghc_windows_task_force

 Differential Revision: https://phabricator.haskell.org/D1340

 GHC Trac Issues: #10955
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10955#comment:4>
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