ARM: 7334/1: add jump label support

Add the arch-specific code to support jump labels for ARM and Thumb-2.

This code will only be activated on compilers that are capable of
building it.  It has been tested with GCC 4.6 patched with the patch
from GCC bug 48637.

Cc: Jason Baron <jbaron@redhat.com>
Signed-off-by: Rabin Vincent <rabin@rab.in>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

5 files changed, 92 insertions, 0 deletions

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 6b5f84887ce5..ee6c7154c9a1 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -9,6 +9,7 @@ config ARM
         select SYS_SUPPORTS_APM_EMULATION
         select GENERIC_ATOMIC64 if (CPU_V6 || !CPU_32v6K || !AEABI)
         select HAVE_OPROFILE if (HAVE_PERF_EVENTS)
+        select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL
         select HAVE_ARCH_KGDB
         select HAVE_KPROBES if !XIP_KERNEL
         select HAVE_KRETPROBES if (HAVE_KPROBES)
diff --git a/arch/arm/include/asm/jump_label.h b/arch/arm/include/asm/jump_label.h
new file mode 100644
index 000000000000..5c5ca2ea62b0
--- /dev/null
+++ b/arch/arm/include/asm/jump_label.h
@@ -0,0 +1,41 @@
+#ifndef _ASM_ARM_JUMP_LABEL_H
+#define _ASM_ARM_JUMP_LABEL_H
+
+#ifdef __KERNEL__
+
+#include <linux/types.h>
+#include <asm/system.h>
+
+#define JUMP_LABEL_NOP_SIZE 4
+
+#ifdef CONFIG_THUMB2_KERNEL
+#define JUMP_LABEL_NOP  "nop.w"
+#else
+#define JUMP_LABEL_NOP  "nop"
+#endif
+
+static __always_inline bool arch_static_branch(struct jump_label_key *key)
+{
+        asm goto("1:\n\t"
+                 JUMP_LABEL_NOP "\n\t"
+                 ".pushsection __jump_table,  \"aw\"\n\t"
+                 ".word 1b, %l[l_yes], %c0\n\t"
+                 ".popsection\n\t"
+                 : :  "i" (key) :  : l_yes);
+
+        return false;
+l_yes:
+        return true;
+}
+
+#endif /* __KERNEL__ */
+
+typedef u32 jump_label_t;
+
+struct jump_entry {
+        jump_label_t code;
+        jump_label_t target;
+        jump_label_t key;
+};
+
+#endif
diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index 8c63ee8d3c48..1b7d9a390971 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -38,6 +38,7 @@ obj-$(CONFIG_HAVE_ARM_SCU)	+= smp_scu.o
 obj-$(CONFIG_HAVE_ARM_TWD)      += smp_twd.o
 obj-$(CONFIG_DYNAMIC_FTRACE)    += ftrace.o insn.o
 obj-$(CONFIG_FUNCTION_GRAPH_TRACER)     += ftrace.o insn.o
+obj-$(CONFIG_JUMP_LABEL)        += jump_label.o insn.o patch.o
 obj-$(CONFIG_KEXEC)             += machine_kexec.o relocate_kernel.o
 obj-$(CONFIG_KPROBES)           += kprobes.o kprobes-common.o patch.o
 ifdef CONFIG_THUMB2_KERNEL
diff --git a/arch/arm/kernel/insn.h b/arch/arm/kernel/insn.h
index 994d60fd3ff5..e96065da4dae 100644
--- a/arch/arm/kernel/insn.h
+++ b/arch/arm/kernel/insn.h
@@ -1,6 +1,16 @@
 #ifndef __ASM_ARM_INSN_H
 #define __ASM_ARM_INSN_H
 
+static inline unsigned long
+arm_gen_nop(void)
+{
+#ifdef CONFIG_THUMB2_KERNEL
+        return 0xf3af8000; /* nop.w */
+#else
+        return 0xe1a00000; /* mov r0, r0 */
+#endif
+}
+
 unsigned long
 __arm_gen_branch(unsigned long pc, unsigned long addr, bool link);
 
diff --git a/arch/arm/kernel/jump_label.c b/arch/arm/kernel/jump_label.c
new file mode 100644
index 000000000000..4ce4f789446d
--- /dev/null
+++ b/arch/arm/kernel/jump_label.c
@@ -0,0 +1,39 @@
+#include <linux/kernel.h>
+#include <linux/jump_label.h>
+
+#include "insn.h"
+#include "patch.h"
+
+#ifdef HAVE_JUMP_LABEL
+
+static void __arch_jump_label_transform(struct jump_entry *entry,
+                                        enum jump_label_type type,
+                                        bool is_static)
+{
+        void *addr = (void *)entry->code;
+        unsigned int insn;
+
+        if (type == JUMP_LABEL_ENABLE)
+                insn = arm_gen_branch(entry->code, entry->target);
+        else
+                insn = arm_gen_nop();
+
+        if (is_static)
+                __patch_text(addr, insn);
+        else
+                patch_text(addr, insn);
+}
+
+void arch_jump_label_transform(struct jump_entry *entry,
+                               enum jump_label_type type)
+{
+        __arch_jump_label_transform(entry, type, false);
+}
+
+void arch_jump_label_transform_static(struct jump_entry *entry,
+                                      enum jump_label_type type)
+{
+        __arch_jump_label_transform(entry, type, true);
+}
+
+#endif