[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>
diff --git a/arch/i386/boot/setup.S b/arch/i386/boot/setup.S
index 3aec4538..9aa8b05 100644
--- a/arch/i386/boot/setup.S
+++ b/arch/i386/boot/setup.S
@@ -588,11 +588,6 @@
call default_switch
rmodeswtch_end:
-# we get the code32 start address and modify the below 'jmpi'
-# (loader may have changed it)
- movl %cs:code32_start, %eax
- movl %eax, %cs:code32
-
# Now we move the system to its rightful place ... but we check if we have a
# big-kernel. In that case we *must* not move it ...
testb $LOADED_HIGH, %cs:loadflags
@@ -788,11 +783,12 @@
a20_done:
#endif /* CONFIG_X86_VOYAGER */
-# set up gdt and idt
+# set up gdt and idt and 32bit start address
lidt idt_48 # load idt with 0,0
xorl %eax, %eax # Compute gdt_base
movw %ds, %ax # (Convert %ds:gdt to a linear ptr)
shll $4, %eax
+ addl %eax, code32
addl $gdt, %eax
movl %eax, (gdt_48+2)
lgdt gdt_48 # load gdt with whatever is
@@ -851,9 +847,26 @@
# Manual, Mixing 16-bit and 32-bit code, page 16-6)
.byte 0x66, 0xea # prefix + jmpi-opcode
-code32: .long 0x1000 # will be set to 0x100000
- # for big kernels
+code32: .long startup_32 # will be set to %cs+startup_32
.word __BOOT_CS
+.code32
+startup_32:
+ movl $(__BOOT_DS), %eax
+ movl %eax, %ds
+ movl %eax, %es
+ movl %eax, %fs
+ movl %eax, %gs
+ movl %eax, %ss
+
+ xorl %eax, %eax
+1: incl %eax # check that A20 really IS enabled
+ movl %eax, 0x00000000 # loop forever if it isn't
+ cmpl %eax, 0x00100000
+ je 1b
+
+ # Jump to the 32bit entry point
+ jmpl *(code32_start - start + (DELTA_INITSEG << 4))(%esi)
+.code16
# Here's a bunch of information about your current kernel..
kernel_version: .ascii UTS_RELEASE