Add ability to produce crash dumps on Windows

It's often hard to debug things like segfaults on Windows,
mostly because gdb isn't always of use and users don't know
how to effectively use it.

This patch provides a way to create a crash drump by passing

`+RTS --generate-crash-dumps` as an option. If any unhandled
exception is triggered a dump is made that contains enough
information to be able to diagnose things successfully.

Currently the created dumps are a bit big because I include
all registers, code and threads information.

This looks like

```
$ testsuite/tests/rts/derefnull.run/derefnull.exe +RTS
--generate-crash-dumps

Access violation in generated code when reading 0000000000000000
Crash dump created. Dump written to:
        E:\msys64\tmp\ghc-20170901-220250-11216-16628.dmp
```

Test Plan: ./validate

Reviewers: austin, hvr, bgamari, erikd, simonmar

Reviewed By: bgamari, simonmar

Subscribers: rwbarton, thomie

Differential Revision: https://phabricator.haskell.org/D3912

2 files changed, 60 insertions, 1 deletions

diff --git a/rts/win32/veh_excn.c b/rts/win32/veh_excn.c
index e45ea2b49c..5105d7676f 100644
--- a/rts/win32/veh_excn.c
+++ b/rts/win32/veh_excn.c
@@ -5,11 +5,18 @@
 * Error Handling implementations for windows
 *
 * ---------------------------------------------------------------------------*/
-
+#define UNICODE 1
 #include "Rts.h"
 #include "ghcconfig.h"
 #include "veh_excn.h"
 #include <assert.h>
+#include <stdbool.h>
+#include <wchar.h>
+#include <windows.h>
+#include <stdio.h>
+#include <excpt.h>
+#include <inttypes.h>
+#include <Dbghelp.h>
 
 /////////////////////////////////
 // Exception / signal handlers.
@@ -80,11 +87,17 @@
 // Registered exception handler
 PVOID __hs_handle = NULL;
 LPTOP_LEVEL_EXCEPTION_FILTER oldTopFilter = NULL;
+bool crash_dump = false;
+bool filter_called = false;
 
 long WINAPI __hs_exception_handler(struct _EXCEPTION_POINTERS *exception_data)
 {
+    if (!crash_dump && filter_called)
+      return EXCEPTION_CONTINUE_EXECUTION;
+
     long action = EXCEPTION_CONTINUE_SEARCH;
     ULONG_PTR what;
+    fprintf (stdout, "\n");
 
     // When the system unwinds the VEH stack after having handled an excn,
     // return immediately.
@@ -119,6 +132,7 @@ long WINAPI __hs_exception_handler(struct _EXCEPTION_POINTERS *exception_data)
         if (EXCEPTION_CONTINUE_EXECUTION == action)
         {
             fflush(stdout);
+            generateDump (exception_data);
             stg_exit(EXIT_FAILURE);
         }
     }
@@ -128,6 +142,7 @@ long WINAPI __hs_exception_handler(struct _EXCEPTION_POINTERS *exception_data)
 
 long WINAPI __hs_exception_filter(struct _EXCEPTION_POINTERS *exception_data)
 {
+    filter_called = true;
     long result = EXCEPTION_CONTINUE_EXECUTION;
     if (oldTopFilter)
     {
@@ -137,6 +152,8 @@ long WINAPI __hs_exception_filter(struct _EXCEPTION_POINTERS *exception_data)
         return result;
     }
 
+    crash_dump = true;
+
     return result;
 }
 
@@ -184,3 +201,42 @@ void __unregister_hs_exception_handler( void )
     }
 }
 
+// Generate a crash dump, however in order for these to generate undecorated
+// names we really need to be able to generate PDB files.
+void generateDump (EXCEPTION_POINTERS* pExceptionPointers)
+{
+    if (!RtsFlags.MiscFlags.generate_dump_file)
+        return;
+
+    WCHAR szPath[MAX_PATH];
+    WCHAR szFileName[MAX_PATH];
+    WCHAR const *const szAppName = L"ghc";
+    WCHAR const *const szVersion = L"";
+    DWORD dwBufferSize = MAX_PATH;
+    HANDLE hDumpFile;
+    SYSTEMTIME stLocalTime;
+    MINIDUMP_EXCEPTION_INFORMATION ExpParam;
+
+    GetLocalTime (&stLocalTime);
+    GetTempPathW (dwBufferSize, szPath);
+
+    swprintf (szFileName, MAX_PATH,
+              L"%ls%ls%ls-%04d%02d%02d-%02d%02d%02d-%ld-%ld.dmp",
+              szPath, szAppName, szVersion,
+              stLocalTime.wYear, stLocalTime.wMonth, stLocalTime.wDay,
+              stLocalTime.wHour, stLocalTime.wMinute, stLocalTime.wSecond,
+              GetCurrentProcessId(), GetCurrentThreadId());
+    hDumpFile = CreateFileW (szFileName, GENERIC_READ|GENERIC_WRITE,
+                FILE_SHARE_WRITE|FILE_SHARE_READ, 0, CREATE_ALWAYS, 0, 0);
+
+    ExpParam.ThreadId          = GetCurrentThreadId();
+    ExpParam.ExceptionPointers = pExceptionPointers;
+    ExpParam.ClientPointers    = TRUE;
+
+    MiniDumpWriteDump(GetCurrentProcess(), GetCurrentProcessId(),
+                      hDumpFile, MiniDumpNormal | MiniDumpWithDataSegs |
+                                 MiniDumpWithThreadInfo | MiniDumpWithCodeSegs,
+                      &ExpParam, NULL, NULL);
+
+    fprintf (stdout, "Crash dump created. Dump written to:\n\t%ls", szFileName);
+}
diff --git a/rts/win32/veh_excn.h b/rts/win32/veh_excn.h
index 72a9967afd..4a2134861c 100644
--- a/rts/win32/veh_excn.h
+++ b/rts/win32/veh_excn.h
@@ -68,3 +68,6 @@ long WINAPI __hs_exception_filter(struct _EXCEPTION_POINTERS *exception_data);
 // prototypes to the functions doing the registration and unregistration of the VEH handlers
 void __register_hs_exception_handler( void );
 void __unregister_hs_exception_handler( void );
+
+// prototypes for dump methods.
+void generateDump(EXCEPTION_POINTERS* pExceptionPointers);