x86, realmode: Replace open-coded ljmpw with a macro

We cannot code an ljmpw to the real-mode segment directly, because gas
refuses to assemble an ljmp with a symbolic segment.  Instead of
open-coding it everywhere, define a macro and use it for this case.

This is specifically an ljmpw from a 16-bit segment.  This is okay, as
one should never enter real mode from a 32-bit segment: if one do, the
CPU ends up in a bizarre (and useless) mode sometimes called "unreal
mode" where segments behave like real mode but the default address and
operand sizes is 32 bits.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/1336501366-28617-15-git-send-email-jarkko.sakkinen@intel.com

1 files changed, 16 insertions, 0 deletions

diff --git a/arch/x86/realmode/rm/realmode.h b/arch/x86/realmode/rm/realmode.h
new file mode 100644
index 000000000000..15ab6335f843
--- /dev/null
+++ b/arch/x86/realmode/rm/realmode.h
@@ -0,0 +1,16 @@
+#ifndef ARCH_X86_REALMODE_RM_REALMODE_H
+#define ARCH_X86_REALMODE_RM_REALMODE_H
+
+#ifdef __ASSEMBLY__
+
+/*
+ * 16-bit ljmpw to the real_mode_seg
+ *
+ * This must be open-coded since gas will choke on using a
+ * relocatable symbol for the segment portion.
+ */
+#define LJMPW_RM(to)    .byte 0xea ; .word (to), real_mode_seg
+
+#endif /* __ASSEMBLY__ */
+
+#endif /* ARCH_X86_REALMODE_RM_REALMODE_H */