Kernel: Clear the x86 DF flag when entering the kernel

The SysV ABI says that the DF flag should be clear on function entry.
That means we have to clear it when jumping into the kernel from some
random userspace context.

Kernel/Arch/i386/CPU.cpp

@@ -55,6 +55,7 @@ asm(
  " pushw %ss\n"
  " popw %ds\n"
  " popw %es\n"
+ " cld\n"
  " call handle_irq\n"
  " popw %es\n"
  " popw %ds\n"
@@ -82,6 +83,7 @@ asm(
  " popw %es\n" \
  " popw %fs\n" \
  " popw %gs\n" \
+ " cld\n" \
  " call exception_" #ec "_handler\n" \
  " popw %gs\n" \
  " popw %gs\n" \
@@ -92,35 +94,36 @@ asm(
  " add $0x4, %esp\n" \
  " iret\n");
 
-#define EH_ENTRY_NO_CODE(ec)  \
+#define EH_ENTRY_NO_CODE(ec) \
  extern "C" void exception_##ec##_handler(RegisterDump); \
- extern "C" void exception_##ec##_entry(); \
- asm( \
- ".globl exception_" #ec "_entry\n" \
- "exception_" #ec "_entry: \n" \
- " pushl $0x0\n" \
- " pusha\n" \
- " pushw %ds\n" \
- " pushw %es\n" \
- " pushw %fs\n" \
- " pushw %gs\n" \
- " pushw %ss\n" \
- " pushw %ss\n" \
- " pushw %ss\n" \
- " pushw %ss\n" \
- " pushw %ss\n" \
- " popw %ds\n" \
- " popw %es\n" \
- " popw %fs\n" \
- " popw %gs\n" \
- " call exception_" #ec "_handler\n" \
- " popw %gs\n" \
- " popw %gs\n" \
- " popw %fs\n" \
- " popw %es\n" \
- " popw %ds\n" \
- " popa\n" \
- " add $0x4, %esp\n" \
+ extern "C" void exception_##ec##_entry(); \
+ asm( \
+ ".globl exception_" #ec "_entry\n" \
+ "exception_" #ec "_entry: \n" \
+ " pushl $0x0\n" \
+ " pusha\n" \
+ " pushw %ds\n" \
+ " pushw %es\n" \
+ " pushw %fs\n" \
+ " pushw %gs\n" \
+ " pushw %ss\n" \
+ " pushw %ss\n" \
+ " pushw %ss\n" \
+ " pushw %ss\n" \
+ " pushw %ss\n" \
+ " popw %ds\n" \
+ " popw %es\n" \
+ " popw %fs\n" \
+ " popw %gs\n" \
+ " cld\n" \
+ " call exception_" #ec "_handler\n" \
+ " popw %gs\n" \
+ " popw %gs\n" \
+ " popw %fs\n" \
+ " popw %es\n" \
+ " popw %ds\n" \
+ " popa\n" \
+ " add $0x4, %esp\n" \
  " iret\n");
 
 static void dump(const RegisterDump& regs)

Kernel/Arch/i386/PIT.cpp

@@ -27,6 +27,7 @@ asm(
  " popw %es\n"
  " popw %fs\n"
  " popw %gs\n"
+ " cld\n"
  " call timer_interrupt_handler\n"
  " popw %gs\n"
  " popw %gs\n"

Kernel/Syscall.cpp

@@ -24,6 +24,7 @@ asm(
  " popw %es\n"
  " popw %fs\n"
  " popw %gs\n"
+ " cld\n"
  " call syscall_trap_entry\n"
  " popw %gs\n"
  " popw %gs\n"