[PATCH 2/4] jump label - base patch

[Jason Baron <jbaron@redhat.com>]

Base jump label patch which creates macros for jump patching. This feature is
dependent on gcc version >= 4.5

Signed-off-by: Jason Baron <jbaron@redhat.com>
---
 arch/x86/include/asm/jump_label.h |   27 +++++++++++
 arch/x86/kernel/Makefile          |    2 +-
 arch/x86/kernel/jump_label.c      |   92 +++++++++++++++++++++++++++++++++++++
 include/asm-generic/vmlinux.lds.h |   11 ++++
 include/linux/jump_label.h        |   53 +++++++++++++++++++++
 5 files changed, 184 insertions(+), 1 deletions(-)
 create mode 100644 arch/x86/include/asm/jump_label.h
 create mode 100644 arch/x86/kernel/jump_label.c
 create mode 100644 include/linux/jump_label.h

diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h
new file mode 100644
index 0000000..21a7b79
--- /dev/null
+++ b/arch/x86/include/asm/jump_label.h
@@ -0,0 +1,27 @@
+#ifndef _ASM_X86_JUMP_LABEL_H
+#define _ASM_X86_JUMP_LABEL_H
+
+#include <asm/nops.h>
+
+#if (__GNUC__ == 4 && __GNUC_MINOR__ >= 5)
+#define __HAVE_ARCH_JUMP_LABEL
+#endif
+
+#ifdef __HAVE_ARCH_JUMP_LABEL
+
+#define JUMP_LABEL(tag, label, cond)                                       \
+	do {								   \
+		static const char __jlstrtab_##tag[]                       \
+		__used __attribute__((section("__jump_strings")))  = #tag; \
+		asm goto ("1:"						   \
+			"jmp %l[" #label "] \n\t"		           \
+			".pushsection __jump_table,  \"a\" \n\t"	   \
+			_ASM_PTR "1b, %l[" #label "], %c0, 0 \n\t"	   \
+			".popsection \n\t"				   \
+			: :  "i" (__jlstrtab_##tag) :  : label);	   \
+	} while (0)
+
+#endif
+
+#endif
+
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 91d4189..b6b3e42 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -32,7 +32,7 @@ GCOV_PROFILE_paravirt.o		:= n
 obj-y			:= process_$(BITS).o signal.o entry_$(BITS).o
 obj-y			+= traps.o irq.o irq_$(BITS).o dumpstack_$(BITS).o
 obj-y			+= time.o ioport.o ldt.o dumpstack.o
-obj-y			+= setup.o x86_init.o i8259.o irqinit.o
+obj-y			+= setup.o x86_init.o i8259.o irqinit.o jump_label.o
 obj-$(CONFIG_X86_VISWS)	+= visws_quirks.o
 obj-$(CONFIG_X86_32)	+= probe_roms_32.o
 obj-$(CONFIG_X86_32)	+= sys_i386_32.o i386_ksyms_32.o
diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
new file mode 100644
index 0000000..207947d
--- /dev/null
+++ b/arch/x86/kernel/jump_label.c
@@ -0,0 +1,92 @@
+#include <linux/jump_label.h>
+#include <linux/memory.h>
+#include <linux/kprobes.h>
+#include <linux/uaccess.h>
+
+#ifdef __HAVE_ARCH_JUMP_LABEL
+
+extern struct jump_entry __start___jump_table[];
+extern struct jump_entry __stop___jump_table[];
+
+DEFINE_MUTEX(jump_label_mutex);
+
+union jump_code_union {
+	char code[RELATIVEJUMP_SIZE];
+	struct {
+		char jump;
+		int offset;
+	} __attribute__((packed));
+};
+
+void jump_label_transform(struct jump_entry *entry, enum jump_label_type type)
+{
+	union jump_code_union code;
+	long jump_length;
+	unsigned char opcode;
+	size_t opcode_length;
+
+	if (entry->type == UNKOWN_JUMP) {
+		if (probe_kernel_read(&opcode, (void *)entry->code, 1))
+			BUG();
+
+		if (opcode == 0xe9)
+			entry->type = LONG_JUMP;
+		else if (opcode == 0xeb)
+			entry->type = SHORT_JUMP;
+		else
+			BUG();
+	}
+
+	if (entry->type == LONG_JUMP)
+		opcode_length = 5;
+	else
+		opcode_length = 2;
+
+	if (type == JUMP_LABEL_ENABLE) {
+		if (entry->type == SHORT_JUMP) {
+			code.code[0] = 0xeb;
+			code.code[1] = 0;
+		} else {
+			code.code[0] = 0xe9;
+			code.offset = 0;
+		}
+	} else {
+		jump_length = entry->target - (entry->code + opcode_length);
+		if (entry->type == SHORT_JUMP) {
+			if ((jump_length > 127 || jump_length < -128)) {
+				BUG();
+			}
+			code.code[0] = 0xeb;
+			code.code[1] = (char)jump_length;
+		} else {
+			if ((jump_length > INT_MAX || jump_length < INT_MIN)) {
+				BUG();
+			}
+			code.code[0] = 0xe9;
+			code.offset = jump_length;
+		}
+	}
+
+	mutex_lock(&text_mutex);
+	text_poke_fixup((void *)entry->code, &code,
+			opcode_length, (void *)entry->code + opcode_length);
+	mutex_unlock(&text_mutex);
+}
+
+int jump_label_update(const char *name, enum jump_label_type type)
+{
+	struct jump_entry *iter;
+	
+	mutex_lock(&jump_label_mutex);
+	for (iter = __start___jump_table; iter < __stop___jump_table; iter++) {
+		if (!strcmp(name, iter->name)) {
+			if (!(system_state == SYSTEM_RUNNING &&
+					(init_kernel_text(iter->code))))
+				jump_label_transform(iter, type);
+		}
+	}
+	mutex_unlock(&jump_label_mutex);
+	return 0;
+}
+
+#endif
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index e7eae37..d2f38e2 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -213,6 +213,7 @@
 		*(__vermagic)		/* Kernel version magic */	\
 		*(__markers_strings)	/* Markers: strings */		\
 		*(__tracepoints_strings)/* Tracepoints: strings */	\
+		*(__jump_strings)/* Jump: strings */	\
 	}								\
 									\
 	.rodata1          : AT(ADDR(.rodata1) - LOAD_OFFSET) {		\
@@ -220,6 +221,8 @@
 	}								\
 									\
 	BUG_TABLE							\
+	JUMP_TABLE							\
+									\
 									\
 	/* PCI quirks */						\
 	.pci_fixup        : AT(ADDR(.pci_fixup) - LOAD_OFFSET) {	\
@@ -564,6 +567,14 @@
 #define BUG_TABLE
 #endif
 
+#define JUMP_TABLE							\
+	. = ALIGN(8);							\
+	__jump_table : AT(ADDR(__jump_table) - LOAD_OFFSET) {		\
+		VMLINUX_SYMBOL(__start___jump_table) = .;		\
+		*(__jump_table)						\
+		VMLINUX_SYMBOL(__stop___jump_table) = .;			\
+	}
+
 #ifdef CONFIG_PM_TRACE
 #define TRACEDATA							\
 	. = ALIGN(4);							\
diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
new file mode 100644
index 0000000..eb0a4ef
--- /dev/null
+++ b/include/linux/jump_label.h
@@ -0,0 +1,53 @@
+#ifndef _LINUX_JUMP_LABEL_H
+#define _LINUX_JUMP_LABEL_H
+
+#include <asm/jump_label.h>
+
+struct jump_entry {
+	unsigned long code;
+	unsigned long target;
+	char *name;
+	unsigned long type;
+};
+
+enum jump_label_type {
+	JUMP_LABEL_ENABLE,
+	JUMP_LABEL_DISABLE
+};
+
+enum jump_label_instruction {
+	UNKOWN_JUMP,
+	SHORT_JUMP,
+	LONG_JUMP
+};
+
+#ifdef __HAVE_ARCH_JUMP_LABEL
+
+extern int jump_label_update(const char *name, enum jump_label_type type);
+
+#define enable_jump_label(name) \
+	jump_label_update(name, JUMP_LABEL_ENABLE);
+
+#define disable_jump_label(name) \
+	jump_label_update(name, JUMP_LABEL_DISABLE);
+
+#else
+
+#define JUMP_LABEL(tag, label, cond)		\
+	if (likely(!cond))			\
+		goto label;
+
+static inline int enable_jump_label(const char *name, enum jump_label_type type)
+{
+	return 0;
+}
+
+static inline int disable_jump_label(const char *name,
+				     enum jump_label_type type)
+{
+	return 0;
+}
+
+#endif
+
+#endif
-- 
1.6.2.5