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>

1 files changed, 17 insertions, 4 deletions

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 5bed94e189fa..c9d6c9ed27e5 100644
--- 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