x32: Allow x32 to be configured

At this point, one should be able to build an x32 kernel.

Note that for now we depend on CONFIG_IA32_EMULATION.  Long term, x32
and IA32 should be detangled.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 5bed94e..c9d6c9e 100644 (file)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2165,9 +2165,9 @@ config IA32_EMULATION
        depends on X86_64
        select COMPAT_BINFMT_ELF
        ---help---
-         Include code to run 32-bit programs under a 64-bit kernel. You should
-         likely turn this on, unless you're 100% sure that you don't have any
-         32-bit programs left.
+         Include code to run legacy 32-bit programs under a
+         64-bit kernel. You should likely turn this on, unless you're
+         100% sure that you don't have any 32-bit programs left.
 
 config IA32_AOUT
        tristate "IA32 a.out support"
@@ -2175,9 +2175,22 @@ config IA32_AOUT
        ---help---
          Support old a.out binaries in the 32bit emulation.
 
+config X86_X32_ABI
+       bool "x32 ABI for 64-bit mode (EXPERIMENTAL)"
+       depends on X86_64 && IA32_EMULATION && EXPERIMENTAL
+       ---help---
+         Include code to run binaries for the x32 native 32-bit ABI
+         for 64-bit processors.  An x32 process gets access to the
+         full 64-bit register file and wide data path while leaving
+         pointers at 32 bits for smaller memory footprint.
+
+         You will need a recent binutils (2.22 or later) with
+         elf32_x86_64 support enabled to compile a kernel with this
+         option set.
+
 config COMPAT
        def_bool y
-       depends on IA32_EMULATION
+       depends on IA32_EMULATION || X86_X32_ABI
 
 config COMPAT_FOR_U64_ALIGNMENT
        def_bool COMPAT