sparc: move kernel to a lower address

The openboot mmu code does not like addresses above 4GB, so load the
kernel to a lower address. It doesn't really matter anyway, because on
sparc the kernel normally lives in a separate address space and uses
special instructions to access userland memory.

See #19597 for details, further changes will be needed here.

Change-Id: Iac6901f275667efef5e64d059daf4c96032a7baf
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3573
Reviewed-by: Adrien Destugues <[email protected]>
Tested-by: Commit checker robot <[email protected]>

headers/private/kernel/arch/sparc/arch_kernel.h

@@ -9,7 +9,11 @@
 #include <arch/cpu.h>
 
 // memory layout
-#define KERNEL_LOAD_BASE_64_BIT 0xffffffff80000000ll
+// FIXME: On sparc, the kernel should live in an independent address space,
+// and does not share addresses with userspace. So, a lot of this doesn't
+// really make sense. See #19597 for discussion.
+// The consequence is that IS_USER_MEMORY cannot work in the way we need.
+#define KERNEL_LOAD_BASE_64_BIT 0x80000000ll
 
 // Base of the kernel address space.
 // KERNEL_BASE is the base of the kernel address space. This differs from the

src/system/ldscripts/sparc/kernel.ld

@@ -13,7 +13,7 @@ PHDRS
 
 SECTIONS
 {
-	. = 0xFFFFFFFF80000000 + SIZEOF_HEADERS;
+	. = 0x80000000 + SIZEOF_HEADERS;
 
 	.interp : { *(.interp) } : text
 	.hash : { *(.hash) }