1 files changed, 78 insertions, 0 deletions
diff --git a/src/pal/src/arch/i386/signalhandlerhelper.cpp b/src/pal/src/arch/i386/signalhandlerhelper.cpp
new file mode 100644
index 0000000000..3369abe093
--- /dev/null
+++ b/src/pal/src/arch/i386/signalhandlerhelper.cpp
@@ -0,0 +1,78 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+#include "pal/dbgmsg.h"
+SET_DEFAULT_DEBUG_CHANNEL(EXCEPT); // some headers have code with asserts, so do this first
+
+#include "pal/palinternal.h"
+#include "pal/context.h"
+#include "pal/signal.hpp"
+#include "pal/utils.h"
+#include <sys/ucontext.h>
+
+/*++
+Function :
+    signal_handler_worker
+
+    Handles signal on the original stack where the signal occured. 
+    Invoked via setcontext.
+
+Parameters :
+    POSIX signal handler parameter list ("man sigaction" for details)
+    returnPoint - context to which the function returns if the common_signal_handler returns
+
+    (no return value)
+--*/
+void ExecuteHandlerOnOriginalStack(int code, siginfo_t *siginfo, void *context, SignalHandlerWorkerReturnPoint* returnPoint)
+{
+    ucontext_t *ucontext = (ucontext_t *)context;
+    size_t faultSp = (size_t)MCREG_Esp(ucontext->uc_mcontext);
+
+    _ASSERTE(IS_ALIGNED(faultSp, 4));
+
+    size_t fakeFrameReturnAddress;
+
+    switch (faultSp & 0xc)
+    {
+        case 0x0:
+            fakeFrameReturnAddress = (size_t)SignalHandlerWorkerReturnOffset0 + (size_t)CallSignalHandlerWrapper0;
+            break;
+        case 0x4:
+            fakeFrameReturnAddress = (size_t)SignalHandlerWorkerReturnOffset4 + (size_t)CallSignalHandlerWrapper4;
+            break;
+        case 0x8:
+            fakeFrameReturnAddress = (size_t)SignalHandlerWorkerReturnOffset8 + (size_t)CallSignalHandlerWrapper8;
+            break;
+        case 0xc:
+            fakeFrameReturnAddress = (size_t)SignalHandlerWorkerReturnOffset12 + (size_t)CallSignalHandlerWrapper12;
+            break;
+    }
+
+    size_t* sp = (size_t*)ALIGN_DOWN(faultSp, 16);
+
+    // Build fake stack frame to enable the stack unwinder to unwind from signal_handler_worker to the faulting instruction
+    *--sp = (size_t)MCREG_Eip(ucontext->uc_mcontext);
+    *--sp = (size_t)MCREG_Ebp(ucontext->uc_mcontext);
+    size_t fp = (size_t)sp;
+    // Align stack
+    sp -= 2; 
+    *--sp = (size_t)returnPoint;
+    *--sp = (size_t)context;
+    *--sp = (size_t)siginfo;
+    *--sp = code;
+    *--sp = fakeFrameReturnAddress;
+
+    // Switch the current context to the signal_handler_worker and the original stack
+    CONTEXT context2;
+    RtlCaptureContext(&context2);
+
+    // We don't care about the other registers state since the stack unwinding restores
+    // them for the target frame directly from the signal context.
+    context2.Esp = (size_t)sp;
+    context2.ResumeEsp = (size_t)sp;
+    context2.Ebp = (size_t)fp;
+    context2.Eip = (size_t)signal_handler_worker;
+
+    RtlRestoreContext(&context2, NULL);
+}