ARM: kvm: implement replacement for ld's LOG2CEIL()

Commit 06f75a1f ("ARM, arm64: kvm: get rid of the bounce
page") uses ld's builtin function LOG2CEIL() to align the
KVM init code to a log2 upper bound of its size. However,
this function turns out to be a fairly recent addition to
binutils, which breaks the build for older toolchains.

So instead, implement a replacement LOG2_ROUNDUP() using
the C preprocessor.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm/kernel/vmlinux.lds.S

@@ -12,6 +12,26 @@
 #include <asm/pgtable.h>
 #endif
 
+/*
+ * Poor man's version of LOG2CEIL(), which is
+ * not available in binutils before v2.24.
+ */
+#define LOG2_ROUNDUP(size) (		\
+	__LOG2_ROUNDUP(size,  2)	\
+	__LOG2_ROUNDUP(size,  3)	\
+	__LOG2_ROUNDUP(size,  4)	\
+	__LOG2_ROUNDUP(size,  5)	\
+	__LOG2_ROUNDUP(size,  6)	\
+	__LOG2_ROUNDUP(size,  7)	\
+	__LOG2_ROUNDUP(size,  8)	\
+	__LOG2_ROUNDUP(size,  9)	\
+	__LOG2_ROUNDUP(size, 10)	\
+	__LOG2_ROUNDUP(size, 11)	\
+	12)
+
+#define __LOG2_ROUNDUP(size, order)	\
+	(size) <= (1 << order) ? order :
+
 #define PROC_INFO							\
 	. = ALIGN(4);							\
 	VMLINUX_SYMBOL(__proc_info_begin) = .;				\
@@ -23,7 +43,7 @@
 	VMLINUX_SYMBOL(__idmap_text_start) = .;				\
 	*(.idmap.text)							\
 	VMLINUX_SYMBOL(__idmap_text_end) = .;				\
-	. = ALIGN(1 << LOG2CEIL(__hyp_idmap_size));			\
+	. = ALIGN(1 << LOG2_ROUNDUP(__hyp_idmap_size));			\
 	VMLINUX_SYMBOL(__hyp_idmap_text_start) = .;			\
 	*(.hyp.idmap.text)						\
 	VMLINUX_SYMBOL(__hyp_idmap_text_end) = .;