fibers: implement switching exception information, fix invalid exception chain

Author: rainers

src/core/thread.d

@@ -3908,6 +3908,10 @@ version( LDC )
         version( X86 ) version = CheckFiberMigration;
         version( X86_64 ) version = CheckFiberMigration;
     }
+    else version( Windows )
+    {
+        version( X86 ) version = CheckFiberMigration;
+    }
 }
 
 // Fiber support for SjLj style exceptions
@@ -4854,16 +4858,21 @@ private:
                 finalHandler = reg.handler;
             }
 
-            pstack -= EXCEPTION_REGISTRATION.sizeof;
+            // With safeseh(?), the chain must not extend to the very top
+            // of the stack, otherwise the exception chain is also considered
+            // invalid. Reserving additional 4 bytes at the top of the stack will
+            // keep the EXCEPTION_REGISTRATION below that limit
+            size_t reserve = EXCEPTION_REGISTRATION.sizeof + 4;
+            pstack -= reserve;
             *(cast(EXCEPTION_REGISTRATION*)pstack) =
                 EXCEPTION_REGISTRATION( sehChainEnd, finalHandler );
 
             push( cast(size_t) &fiber_entryPoint );                 // EIP
-            push( cast(size_t) m_ctxt.bstack - EXCEPTION_REGISTRATION.sizeof ); // EBP
+            push( cast(size_t) m_ctxt.bstack - reserve );           // EBP
             push( 0x00000000 );                                     // EDI
             push( 0x00000000 );                                     // ESI
             push( 0x00000000 );                                     // EBX
-            push( cast(size_t) m_ctxt.bstack - EXCEPTION_REGISTRATION.sizeof ); // FS:[0]
+            push( cast(size_t) m_ctxt.bstack - reserve );           // FS:[0]
             push( cast(size_t) m_ctxt.bstack );                     // FS:[4]
             push( cast(size_t) m_ctxt.bstack - m_size );            // FS:[8]
             push( 0x00000000 );                                     // EAX

src/ldc/eh/common.d

@@ -36,6 +36,9 @@ extern(C) void fatalerror(in char* format, ...)
     abort();
 }
 
+version(Win32) {} else version = notMSVC;
+version(notMSVC):
+
 // ------------------------
 //    Reading DWARF data
 // ------------------------

src/ldc/eh/win32.d

@@ -278,7 +278,14 @@ nothrow:
 
     @property size_t length() const { return _length; }
     @property bool empty() const { return !length; }
-
+
+    void swap(ref ExceptionStack other)
+    {
+        auto olength = other._length; other._length = _length; _length = olength;
+        auto op      = other._p;      other._p      = _p;      _p = op;
+        auto ocap    = other._cap;    other._cap    = _cap;    _cap = ocap;
+    }
+
 private:
     void grow()
     {
@@ -458,7 +465,66 @@ int doRtlUnwind(void* pFrame, ExceptionRecord* eRecord, typeof(RtlUnwind)* handl
         ret;
     }
 }
+
+///////////////////////////////////////////////////////////////
+struct FiberContext
+{
+    ExceptionStack exceptionStack;
+    void* currentException;
+    void* currentExceptionContext;
+    int processingContext;
+}
+
+FiberContext* fiberContext;
+
+extern(C) void** __current_exception() nothrow;
+extern(C) void** __current_exception_context() nothrow;
+extern(C) int* __processing_throw() nothrow;
+
+extern(C) void* _d_eh_swapContext(FiberContext* newContext) nothrow
+{
+    import rt.util.container.common : xmalloc;
+    import core.stdc.string : memset;
+    if (!fiberContext)
+    {
+        fiberContext = cast(FiberContext*) xmalloc(FiberContext.sizeof);
+        memset(fiberContext, 0, FiberContext.sizeof);
+    }
+    fiberContext.exceptionStack.swap(exceptionStack);
+    fiberContext.currentException = *__current_exception();
+    fiberContext.currentExceptionContext = *__current_exception_context();
+    fiberContext.processingContext = *__processing_throw();
+
+    if (newContext)
+    {
+        exceptionStack.swap(newContext.exceptionStack);
+        *__current_exception() = newContext.currentException;
+        *__current_exception_context() = newContext.currentExceptionContext;
+        *__processing_throw() = newContext.processingContext;
+    }
+    else
+    {
+        exceptionStack = ExceptionStack();
+        *__current_exception() = null;
+        *__current_exception_context() = null;
+        *__processing_throw() = 0;
+    }
+
+    FiberContext* old = fiberContext;
+    fiberContext = newContext;
+    return old;
+}
 
+static ~this()
+{
+    import core.stdc.stdlib : free;
+    if (fiberContext)
+    {
+        destroy(*fiberContext);
+        free(fiberContext);
+    }
+}
+
 ///////////////////////////////////////////////////////////////
 void msvc_eh_init()
 {