From 555300d680ef689ad554abf8945db469f9329799 Mon Sep 17 00:00:00 2001
From: Timo Kreuzer <timo.kreuzer@reactos.org>
Date: Sun, 1 Oct 2017 14:34:26 +0000
Subject: [PATCH] [RTL/x64] Support frames to skip in flags to
 RtlWalkFrameChain

svn path=/trunk/; revision=76019
---
 reactos/sdk/lib/rtl/amd64/unwind.c | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/reactos/sdk/lib/rtl/amd64/unwind.c b/reactos/sdk/lib/rtl/amd64/unwind.c
index c909250eaf3..f9af729ce88 100644
--- a/reactos/sdk/lib/rtl/amd64/unwind.c
+++ b/reactos/sdk/lib/rtl/amd64/unwind.c
@@ -524,11 +524,14 @@ RtlWalkFrameChain(OUT PVOID *Callers,
     ULONG64 ControlPc, ImageBase, EstablisherFrame;
     ULONG64 StackLow, StackHigh;
     PVOID HandlerData;
-    ULONG i;
+    ULONG i, FramesToSkip;
     PRUNTIME_FUNCTION FunctionEntry;
 
     DPRINT("Enter RtlWalkFrameChain\n");
 
+    /* The upper bits in Flags define how many frames to skip */
+    FramesToSkip = Flags >> 8;
+
     /* Capture the current Context */
     RtlCaptureContext(&Context);
     ControlPc = Context.Rip;
@@ -537,12 +540,12 @@ RtlWalkFrameChain(OUT PVOID *Callers,
     RtlpGetStackLimits(&StackLow, &StackHigh);
 
     /* Check if we want the user-mode stack frame */
-    if (Flags == 1)
+    if (Flags & 1)
     {
     }
 
     /* Loop the frames */
-    for (i = 0; i < Count; i++)
+    for (i = 0; i < FramesToSkip + Count; i++)
     {
         /* Lookup the FunctionEntry for the current ControlPc */
         FunctionEntry = RtlLookupFunctionEntry(ControlPc, &ImageBase, NULL);
@@ -579,9 +582,14 @@ RtlWalkFrameChain(OUT PVOID *Callers,
             break;
         }
 
-        /* Save this frame and continue with new Rip */
+        /* Continue with new Rip */
         ControlPc = Context.Rip;
-        Callers[i] = (PVOID)ControlPc;
+
+        /* Save value, if we are past the frames to skip */
+        if (i >= FramesToSkip)
+        {
+            Callers[i - FramesToSkip] = (PVOID)ControlPc;
+        }
     }
 
     DPRINT("RtlWalkFrameChain returns %ld\n", i);
@@ -605,14 +613,8 @@ RtlGetCallersAddress(
      * RtlWalkFrameChain -> RtlGetCallersAddress -> x -> y */
     Number = RtlWalkFrameChain(Callers, 4, 0);
 
-    if (CallersAddress)
-    {
-        *CallersAddress = (Number >= 3) ? Callers[2] : NULL;
-    }
-    if (CallersCaller)
-    {
-        *CallersCaller = (Number == 4) ? Callers[3] : NULL;
-    }
+    *CallersAddress = (Number >= 3) ? Callers[2] : NULL;
+    *CallersCaller = (Number == 4) ? Callers[3] : NULL;
 
     return;
 }
-- 
2.17.1