From bc625510ddf3ee2ba14e41d37c73394028e2c62c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Cl=C3=A9ment=20Gallet?= <clement.gallet@ens-lyon.org>
Date: Tue, 16 Oct 2018 12:23:09 +0200
Subject: [PATCH] Save and restore the first stack frame of the alternate stack

---
 CHANGELOG.md                         |  1 +
 src/libTAS/checkpoint/AltStack.cpp   | 17 +++++++++++++++++
 src/libTAS/checkpoint/AltStack.h     |  3 +++
 src/libTAS/checkpoint/Checkpoint.cpp |  7 +++++++
 4 files changed, 28 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3830efbc..38bcc742 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -22,6 +22,7 @@
 * Fix SDL1 keyboard layout
 * Wait for threads to register
 * Detect auto-repeat cases when detectable auto-repeat is not supported by the server
+* Fix crash when loading a savestate on a non-draw frame
 
 ## [1.3.1] - 2018-08-30
 ### Added
diff --git a/src/libTAS/checkpoint/AltStack.cpp b/src/libTAS/checkpoint/AltStack.cpp
index ae2f3ef4..12f021d4 100644
--- a/src/libTAS/checkpoint/AltStack.cpp
+++ b/src/libTAS/checkpoint/AltStack.cpp
@@ -34,6 +34,13 @@ namespace libtas {
  */
 static stack_t oss;
 
+/* We must save the last stack frame of the alternate stack in the savestate, so
+ * that we return at the correct location from the alternate stack.
+ */
+#define STACKFRAME_OFFSET 0x700
+#define STACKFRAME_SIZE 0x700
+static uint8_t stack_frame[STACKFRAME_SIZE];
+
 void AltStack::saveStack()
 {
     int ret;
@@ -62,4 +69,14 @@ void AltStack::restoreStack()
     MYASSERT(ret == 0)
 }
 
+void AltStack::saveStackFrame()
+{
+    memcpy(stack_frame, ReservedMemory::getAddr(ReservedMemory::STACK_ADDR + ReservedMemory::STACK_SIZE - STACKFRAME_OFFSET), STACKFRAME_SIZE);
+}
+
+void AltStack::restoreStackFrame()
+{
+    memcpy(ReservedMemory::getAddr(ReservedMemory::STACK_ADDR + ReservedMemory::STACK_SIZE - STACKFRAME_OFFSET), stack_frame, STACKFRAME_SIZE);
+}
+
 }
diff --git a/src/libTAS/checkpoint/AltStack.h b/src/libTAS/checkpoint/AltStack.h
index f9446fc4..b0694401 100644
--- a/src/libTAS/checkpoint/AltStack.h
+++ b/src/libTAS/checkpoint/AltStack.h
@@ -28,6 +28,9 @@ namespace AltStack
     void saveStack();
     void prepareStack();
     void restoreStack();
+
+    void saveStackFrame();
+    void restoreStackFrame();
 };
 }
 
diff --git a/src/libTAS/checkpoint/Checkpoint.cpp b/src/libTAS/checkpoint/Checkpoint.cpp
index 55c278d5..802c8026 100644
--- a/src/libTAS/checkpoint/Checkpoint.cpp
+++ b/src/libTAS/checkpoint/Checkpoint.cpp
@@ -21,6 +21,7 @@
 
 #include "Checkpoint.h"
 #include "ThreadManager.h"
+#include "AltStack.h"
 #include "../logging.h"
 #include "ProcMapsArea.h"
 #include "ProcSelfMaps.h"
@@ -308,6 +309,9 @@ void Checkpoint::handler(int signum)
 
         /* Restore the entire xcb connection struct */
         memcpy(cur_xcb_conn, &xcb_conn, sizeof(xcb_connection_t));
+
+        /* We must restore the current stack frame from the savestate */
+        AltStack::restoreStackFrame();
     }
     else {
         /* Check that base savestate exists, otherwise save it */
@@ -326,6 +330,9 @@ void Checkpoint::handler(int signum)
             }
         }
 
+        /* We must store the current stack frame in the savestate */
+        AltStack::saveStackFrame();
+
         writeAllAreas(false);
     }
     debuglogstdio(LCF_CHECKPOINT, "End restore.");