[PATCH] i386: Relocatable kernel support

This patch modifies the i386 kernel so that if CONFIG_RELOCATABLE is
selected it will be able to be loaded at any 4K aligned address below
1G.  The technique used is to compile the decompressor with -fPIC and
modify it so the decompressor is fully relocatable.  For the main
kernel relocations are generated.  Resulting in a kernel that is relocatable
with no runtime overhead and no need to modify the source code.

A reserved 32bit word in the parameters has been assigned
to serve as a stack so we figure out where are running.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
Signed-off-by: Andi Kleen <ak@suse.de>

1 files changed, 24 insertions, 4 deletions

diff --git a/arch/i386/boot/compressed/Makefile b/arch/i386/boot/compressed/Makefile
index 258ea95224f6..cc28da3a881e 100644
--- a/arch/i386/boot/compressed/Makefile
+++ b/arch/i386/boot/compressed/Makefile
@@ -4,22 +4,42 @@
 # create a compressed vmlinux image from the original vmlinux
 #
 
-targets         := vmlinux vmlinux.bin vmlinux.bin.gz head.o misc.o piggy.o
+targets         := vmlinux vmlinux.bin vmlinux.bin.gz head.o misc.o piggy.o \
+                        vmlinux.bin.all vmlinux.relocs
 EXTRA_AFLAGS    := -traditional
 
-LDFLAGS_vmlinux := -Ttext $(IMAGE_OFFSET) -e startup_32
+LDFLAGS_vmlinux := -T
+CFLAGS_misc.o += -fPIC
+hostprogs-y     := relocs
 
-$(obj)/vmlinux: $(obj)/head.o $(obj)/misc.o $(obj)/piggy.o FORCE
+$(obj)/vmlinux: $(src)/vmlinux.lds $(obj)/head.o $(obj)/misc.o $(obj)/piggy.o FORCE
         $(call if_changed,ld)
         @:
 
 $(obj)/vmlinux.bin: vmlinux FORCE
         $(call if_changed,objcopy)
 
+quiet_cmd_relocs = RELOCS  $@
+      cmd_relocs = $(obj)/relocs $< > $@
+$(obj)/vmlinux.relocs: vmlinux $(obj)/relocs FORCE
+        $(call if_changed,relocs)
+
+vmlinux.bin.all-y := $(obj)/vmlinux.bin
+vmlinux.bin.all-$(CONFIG_RELOCATABLE) += $(obj)/vmlinux.relocs
+quiet_cmd_relocbin = BUILD   $@
+      cmd_relocbin = cat $(filter-out FORCE,$^) > $@
+$(obj)/vmlinux.bin.all: $(vmlinux.bin.all-y) FORCE
+        $(call if_changed,relocbin)
+
+ifdef CONFIG_RELOCATABLE
+$(obj)/vmlinux.bin.gz: $(obj)/vmlinux.bin.all FORCE
+        $(call if_changed,gzip)
+else
 $(obj)/vmlinux.bin.gz: $(obj)/vmlinux.bin FORCE
         $(call if_changed,gzip)
+endif
 
 LDFLAGS_piggy.o := -r --format binary --oformat elf32-i386 -T
 
-$(obj)/piggy.o: $(obj)/vmlinux.scr $(obj)/vmlinux.bin.gz FORCE
+$(obj)/piggy.o: $(src)/vmlinux.scr $(obj)/vmlinux.bin.gz FORCE
         $(call if_changed,ld)