lkl: handle ro_after_init properlly

Since section ro_after_init contains writable data located inside
.rodata section (which is read-only), resulting rodata section is
writable.  Since we don't have implementation of mark_rodata_ro() in our
arch, those section keep writable forever.

So this commit moves data.ro_after_init section from rodata to the
end of sections so that rodata section will be read-only.

Without this commit there is no issue, but valgrind somehow puzzled with
malformed sections when ro_after_init section used, and results
unresolved symbols after a valgrind run.

This commit fixes torvalds#349.

Fixes: d2ec3f7 ("pty: make ptmx file ops read-only after init")

The commit uses (d07a980, s390: add
proper __ro_after_init support) as a reference.

Signed-off-by: Hajime Tazaki <thehajime@gmail.com>

arch/lkl/include/asm/vmlinux.lds.h

@@ -1,6 +1,9 @@
 #ifndef _LKL_VMLINUX_LDS_H
 #define _LKL_VMLINUX_LDS_H
 
+/* we encode our own __ro_after_init section */
+#define RO_AFTER_INIT_DATA
+
 #ifdef __MINGW32__
 #define RODATA_SECTION .rdata
 #endif

arch/lkl/kernel/vmlinux.lds.S

@@ -33,7 +33,10 @@ SECTIONS
 	RW_DATA_SECTION(L1_CACHE_BYTES, PAGE_SIZE, THREAD_SIZE)
 	VMLINUX_SYMBOL(_edata) = .;
 
+	VMLINUX_SYMBOL(__start_ro_after_init) = .;
+	.data..ro_after_init : { *(.data..ro_after_init)}
 	EXCEPTION_TABLE(16)
+	VMLINUX_SYMBOL(__end_ro_after_init) = .;
 	NOTES
 
 	BSS_SECTION(0, 0, 0)