[GHC] #6079: SEH exception handler not implemented on Win64

[GHC]

#6079: SEH exception handler not implemented on Win64
-------------------------------------+-------------------------------------
        Reporter:  igloo             |                   Owner:  Phyx-
            Type:  bug               |                  Status:  patch
        Priority:  normal            |               Milestone:  7.12.1
       Component:  Runtime System    |                 Version:  7.5
      Resolution:                    |                Keywords:
Operating System:  Windows           |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:  derefnull,
 Related Tickets:                    |  divbyzero
                                     |                Blocking:
                                     |  Differential Revisions:  Phab:D691
-------------------------------------+-------------------------------------

Comment (by Austin Seipp <austin@…>):

 In [changeset:"5200bdeb26c5ec98739b14b10fc8907296bceeb9/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="5200bdeb26c5ec98739b14b10fc8907296bceeb9"
 Replaced SEH handles with VEH handlers which should work uniformly across
 x86 and x64

 Summary:
 On Windows, the default action for things like division by zero and
 segfaults is to pop up a Dr. Watson error reporting dialog if the
 exception
 is unhandled by the user code.

 This is a pain when we are SSHed into a Windows machine, or when we
 want to debug a problem with gdb (gdb will get a first and second chance
 to
 handle the exception, but if it doesn't the pop-up will show).

 veh_excn provides two macros, `BEGIN_CATCH` and `END_CATCH`, which
 will catch such exceptions in the entire process and die by
 printing a message and calling `stg_exit(1)`.

 Previously this code was handled using SEH (Structured Exception Handlers)
 however each compiler and platform have different ways of dealing with
 SEH.

 `MSVC` compilers have the keywords `__try`, `__catch` and `__except` to
 have the
 compiler generate the appropriate SEH handler code for you.

 `MinGW` compilers have no such keywords and require you to manually set
 the
 SEH Handlers, however because SEH is implemented differently in x86 and
 x64
 the methods to use them in GCC differs.

 `x86`: SEH is based on the stack, the SEH handlers are available at
 `FS[0]`.
      On startup one would only need to add a new handler there. This has
      a number of issues such as hard to share handlers and it can be
 exploited.

 `x64`: In order to fix the issues with the way SEH worked in x86, on x64
 SEH handlers
      are statically compiled and added to the .pdata section by the
 compiler.
      Instead of being thread global they can now be Image global since you
 have to
      specify the `RVA` of the region of code that the handlers govern.

 You can on x64 Dynamically allocate SEH handlers, but it seems that (based
 on
 experimentation and it's very under-documented) that the dynamic calls
 cannot override
 static SEH handlers in the .pdata section.

 Because of this and because GHC no longer needs to support < windows XP,
 the better
 alternative for handling errors would be using the in XP introduced VEH.

 The bonus is because VEH (Vectored Exception Handler) are a runtime
 construct the API
 is the same for both x86 and x64 (note that the Context object does
 contain CPU specific
 structures) and the calls are the same cross compilers. Which means this
 file can be
 simplified quite a bit.
 Using VEH also means we don't have to worry about the dynamic code
 generated by GHCi.

 Test Plan:
 Prior to this diff the tests for `derefnull` and `divbyzero` seem to have
 been disabled for windows.
 To reproduce the issue on x64:
 1) open ghci
 2) import GHC.Base
 3) run: 1 `divInt` 0

 which should lead to ghci crashing an a watson error box displaying.

 After applying the patch, run:

 make TEST="derefnull divbyzero"

 on both x64 and x86 builds of ghc to verify fix.

 Reviewers: simonmar, austin

 Reviewed By: austin

 Subscribers: thomie

 Differential Revision: https://phabricator.haskell.org/D691

 GHC Trac Issues: #6079
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/6079#comment:13>
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