Switch VEH to VCH and allow disabling of SEH completely.

Exception handling on Windows is unfortunately a bit complicated.
But essentially the VEH Handlers we currently have are running too
early.

This was a problem as it ran so early it also swallowed C++ exceptions
and other software exceptions which the system could have very well
recovered from.

So instead we use a sequence of chains to for the exception handlers to
run as late as possible. You really can't get any later than this.

Please read the comment in the patch for more details.

I'm also providing a switch to allow people to turn off the exception
handling entirely. In case it does present a problem with their code.

Test Plan: ./validate

Reviewers: austin, hvr, bgamari, erikd, simonmar

Reviewed By: bgamari

Subscribers: rwbarton, thomie

GHC Trac Issues: #13911, #12110

Differential Revision: https://phabricator.haskell.org/D3911

1 files changed, 8 insertions, 0 deletions

diff --git a/docs/users_guide/runtime_control.rst b/docs/users_guide/runtime_control.rst
index f141c323f6..7afc7262f8 100644
--- a/docs/users_guide/runtime_control.rst
+++ b/docs/users_guide/runtime_control.rst
@@ -220,6 +220,14 @@ Miscellaneous RTS options
     capabilities. To disable the timer signal, use the ``-V0`` RTS
     option (see above).
 
+.. rts-flag:: --install-seh-handlers=⟨yes|no⟩
+
+    If yes (the default), the RTS on Windows installs exception handlers to
+    catch unhandled exceptions using the Windows exception handling mechanism.
+    This option is primarily useful for when you are using the Haskell code as a
+    DLL, and don't want the RTS to ungracefully terminate your application on
+    erros such as segfaults.
+
 .. rts-flag:: -xm ⟨address⟩
 
     .. index::