[PATCH] uml: allow building as 32-bit binary on 64bit host

This patch makes the command:

make ARCH=um SUBARCH=i386

work on x86_64 hosts (with support for building 32-bit binaries).  This is
especially needed since 64-bit UMLs don't support 32-bit emulation for guest
binaries, currently.  This has been tested in all possible cases and works.

Only exception is that I've built but not tested a 64-bit binary, because I
hadn't a 64-bit filesystem available.

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Cc: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 21 insertions, 10 deletions

diff --git a/arch/um/Makefile-i386 b/arch/um/Makefile-i386
index 301059062a3..93d0818fa81 100644
--- a/arch/um/Makefile-i386
+++ b/arch/um/Makefile-i386
@@ -1,4 +1,4 @@
-SUBARCH_CORE := arch/um/sys-i386/ arch/i386/crypto/
+core-y += arch/um/sys-i386/ arch/i386/crypto/
 
 TOP_ADDR := $(CONFIG_TOP_ADDR)
 
@@ -8,21 +8,32 @@ ifeq ($(CONFIG_MODE_SKAS),y)
   endif
 endif
 
+LDFLAGS                 += -m elf_i386
+ELF_ARCH                := $(SUBARCH)
+ELF_FORMAT              := elf32-$(SUBARCH)
+OBJCOPYFLAGS            := -O binary -R .note -R .comment -S
+
+ifeq ("$(origin SUBARCH)", "command line")
+ifneq ("$(shell uname -m | sed -e s/i.86/i386/)", "$(SUBARCH)")
+CFLAGS                  += $(call cc-option,-m32)
+USER_CFLAGS             += $(call cc-option,-m32)
+HOSTCFLAGS              += $(call cc-option,-m32)
+HOSTLDFLAGS             += $(call cc-option,-m32)
+AFLAGS                  += $(call cc-option,-m32)
+LINK-y                  += $(call cc-option,-m32)
+UML_OBJCOPYFLAGS        += -F $(ELF_FORMAT)
+
+export LDFLAGS HOSTCFLAGS HOSTLDFLAGS UML_OBJCOPYFLAGS
+endif
+endif
+
 CFLAGS += -U__$(SUBARCH)__ -U$(SUBARCH) $(STUB_CFLAGS)
-ARCH_USER_CFLAGS :=
 
 ifneq ($(CONFIG_GPROF),y)
 ARCH_CFLAGS += -DUM_FASTCALL
 endif
 
-ELF_ARCH := $(SUBARCH)
-ELF_FORMAT := elf32-$(SUBARCH)
-
-OBJCOPYFLAGS  := -O binary -R .note -R .comment -S
-
-SYS_UTIL_DIR    := $(ARCH_DIR)/sys-i386/util
-
-SYS_HEADERS := $(SYS_DIR)/sc.h $(SYS_DIR)/thread.h
+SYS_HEADERS     := $(SYS_DIR)/sc.h $(SYS_DIR)/thread.h
 
 prepare: $(SYS_HEADERS)