From a5c293a87f919351d7e6380f81066a19dee3d092 Mon Sep 17 00:00:00 2001
From: sonic <sonic@fb15a70f-31f2-0310-bbcc-cdcc74a49acc>
Date: Thu, 22 Dec 2011 06:18:19 +0000
Subject: [PATCH] Support red zone on x86-64

git-svn-id: https://svn.aros.org/svn/aros/trunk/AROS@43164 fb15a70f-31f2-0310-bbcc-cdcc74a49acc
---
 arch/all-mingw32/kernel/host_intern.h           |  1 +
 arch/all-mingw32/kernel/host_intr.c             | 12 +++++++-
 arch/all-mingw32/kernel/leaveinterrupt_x86_64.s | 41 ++++++++++++++++++++-----
 3 files changed, 45 insertions(+), 9 deletions(-)
 rewrite arch/all-mingw32/kernel/leaveinterrupt_x86_64.s (74%)

diff --git a/arch/all-mingw32/kernel/host_intern.h b/arch/all-mingw32/kernel/host_intern.h
index 35eb5b6e56..12b4b9c9ff 100644
--- a/arch/all-mingw32/kernel/host_intern.h
+++ b/arch/all-mingw32/kernel/host_intern.h
@@ -13,3 +13,4 @@ struct LeaveInterruptContext
 extern HANDLE conin, conout;
 
 void core_LeaveInterrupt(void);
+extern unsigned char core_LeaveInt_End;
diff --git a/arch/all-mingw32/kernel/host_intr.c b/arch/all-mingw32/kernel/host_intr.c
index 2f194f9f6d..0d5d7a1ad2 100644
--- a/arch/all-mingw32/kernel/host_intr.c
+++ b/arch/all-mingw32/kernel/host_intr.c
@@ -119,6 +119,16 @@ LONG WINAPI exceptionHandler(EXCEPTION_POINTERS *exptr)
     return EXCEPTION_CONTINUE_EXECUTION;
 }
 
+#ifdef __x86_64__
+/*
+ * Magic: on x86-64 we can't preempt within a certain location. Not good,
+ * but i can't offer something better. See leaveinterrupt_x86_64.s.
+ */
+#define INT_SAFE(ctx) ((ctx.Rip < (DWORD64)core_LeaveInterrupt) || (ctx.Rip >= (DWORD64)&core_LeaveInt_End))
+#else
+#define INT_SAFE(ctx) TRUE
+#endif
+
 DWORD WINAPI TaskSwitcher()
 {
     DWORD obj;
@@ -144,7 +154,7 @@ DWORD WINAPI TaskSwitcher()
         }
 
         /* Process interrupts if we are allowed to */
-        if (Ints_Enabled)
+        if (Ints_Enabled && INT_SAFE(MainCtx))
         {
             Supervisor = 1;
             /* 
diff --git a/arch/all-mingw32/kernel/leaveinterrupt_x86_64.s b/arch/all-mingw32/kernel/leaveinterrupt_x86_64.s
dissimilarity index 74%
index 23b87cdf53..2f5dc56db1 100644
--- a/arch/all-mingw32/kernel/leaveinterrupt_x86_64.s
+++ b/arch/all-mingw32/kernel/leaveinterrupt_x86_64.s
@@ -1,8 +1,33 @@
-        .globl  core_LeaveInterrupt
-
-core_LeaveInterrupt:
-	pushq 0(%rax)		# Push real return address
-	pushq 8(%rax)		# Push real rax contents
-	movl $1, Ints_Enabled	# Now enable interrupts
-	popq %rax		# Restore rax and leave
-	ret
+#
+#   Copyright © 2010-2011, The AROS Development Team. All rights reserved.
+#   $Id$
+#
+#   Desc: Exit from emulated interrupt with enabling, x86-64 version
+#   Lang: English
+#
+
+# Theory of operation:
+# x86-64 has red zone of 128 bytes below the rsp. This makes it impossible to use
+# push/pop instructions here, unlike on i386, because doing this will destroy
+# red zone data.
+# Here we skip the red zone and use -128(%rsp) as our intermediate storage. However,
+# there's an important problem with this. x86 is not ARM, and we can't do something like
+# "addq $128, %rsp; jmpq *-128(rsp)" atomically. This mean, we can be preempted right before
+# the final jump. This is dangerous, because next time we will get back here with our own
+# address in 0(%rax), overwriting -128(rsp) with it and causing infinite loop.
+# In order to work around this issue, interrupt thread checks rip value, and if rip is
+# pointing at this code, interrupts are considered disabled.
+# We still have to use stack for temporary storage because we first need to restore rax
+# and only then jump to return address.
+
+        .globl  core_LeaveInterrupt
+        .globl  core_LeaveInt_End
+
+core_LeaveInterrupt:
+        movq    %rbx, -128(%rsp)    # Save rbx
+        movq    0(%rax), %rbx       # Get real return address into rbx
+        xchg    %rbx, -128(%rsp)    # Remember return address and restore rbx
+	movq    8(%rax), %rax	    # Restore real rax contents
+	movl    $1, Ints_Enabled    # Now enable interrupts
+	jmpq    *-128(%rsp)         # And jump to the needed address
+core_LeaveInt_End:
-- 
2.11.4.GIT