From f838a751cf0bb3f6edd03fec2b7c275fcdf1ab8a Mon Sep 17 00:00:00 2001
From: Stefan Lankes <slankes@eonerc.rwth-aachen.de>
Date: Sun, 15 May 2016 07:48:30 +0200
Subject: [PATCH] clear the DF flag to adhere the x86_64 ABI

---
 hermit/arch/x86/kernel/entry.asm | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/hermit/arch/x86/kernel/entry.asm b/hermit/arch/x86/kernel/entry.asm
index 57cb2f4c2..a2bfc7897 100644
--- a/hermit/arch/x86/kernel/entry.asm
+++ b/hermit/arch/x86/kernel/entry.asm
@@ -114,6 +114,10 @@ start64:
     mov fs, eax
     mov gs, eax
 
+    ; clear DF flag => default value by entering a function
+    ; => see ABI
+    cld
+
     ; determine full image size
     mov rax, kernel_end
     sub rax, kernel_start
@@ -464,6 +468,8 @@ isrsyscall:
 global switch_context
 align 16
 switch_context:
+    ; by entering a function the DF flag has to be cleared => see ABI
+    cld
     ; create on the stack a pseudo interrupt
     ; afterwards, we switch to the task with iret
     push QWORD 0x10             ; SS