[x86 setup 13/33] Header file to produce 16-bit code with gcc

["H. Peter Anvin" <hpa@zytor.com>]

From: H. Peter Anvin <hpa@zytor.com>

gcc for i386 can be used with the assembly prefix ".code16gcc" to generate
16-bit (real-mode) code.  This header file provides the assembly prefix.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
---
 arch/i386/boot/code16gcc.h |   15 +++++++++++++++
 1 files changed, 15 insertions(+), 0 deletions(-)
 create mode 100644 arch/i386/boot/code16gcc.h

diff --git a/arch/i386/boot/code16gcc.h b/arch/i386/boot/code16gcc.h
new file mode 100644
index 0000000..3bd8480
--- /dev/null
+++ b/arch/i386/boot/code16gcc.h
@@ -0,0 +1,15 @@
+/*
+ * code16gcc.h
+ *
+ * This file is -include'd when compiling 16-bit C code.
+ * Note: this asm() needs to be emitted before gcc omits any code.
+ * Depending on gcc version, this requires -fno-unit-at-a-time or
+ * -fno-toplevel-reorder.
+ *
+ * Hopefully gcc will eventually have a real -m16 option so we can
+ * drop this hack long term.
+ */
+
+#ifndef __ASSEMBLY__
+asm(".code16gcc");
+#endif
-- 
1.5.2.2

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