openrisc: Add jump label support

Supported a complete jump_label implementation based on the ARM64 and
RV64 version and add the CONFIG_JUMP_LABEL=y to the defconfig.

Testing was conducted using a dedicated test module jump-label-test,
provided in the link below. For detailed steps, please refer to the
README also at the provided link.

Link: https://github.com/ChenMiaoi/GSoC-2025-Final-Report/tree/main/tests/jump-label-test

Test Environment:
  - Hardware: QEMU emulated OR1K
  - Kernel Version: 6.17.0-rc3-dirty
  - Configs: CONFIG_MODULES=y,CONFIG_MODULE_UNLOAD=y
  - Toolchain: or1k-none-linux-musl-gcc 15.1.0

Test Results:
$ insmod jump_label_test.ko
[   32.590000] Jump label performance test module loaded
[   35.250000] Normal branch time: 1241327150 ns (124 ns per iteration)
[   35.250000] Jump label (false) time: 706422700 ns (70 ns per iteration)
[   35.250000] Jump label (true) time: 708913450 ns (70 ns per iteration)
$ rmmod jump_label_test.ko
[   72.210000] Jump label test module unloaded

The results show approximately 43% improvement in branch performance
when using jump labels compared to traditional branches.

Link: https://lore.kernel.org/openrisc/aLsZ9S3X0OpKy1RM@antec/T/#u
Signed-off-by: chenmiao <chenmiao.ku@gmail.com>
Signed-off-by: Stafford Horne <shorne@gmail.com>

2 files changed, 75 insertions, 0 deletions

diff --git a/arch/openrisc/include/asm/insn-def.h b/arch/openrisc/include/asm/insn-def.h
index e28a9a9604fc..1e0c028a5b95 100644
--- a/arch/openrisc/include/asm/insn-def.h
+++ b/arch/openrisc/include/asm/insn-def.h
@@ -9,4 +9,7 @@
 /* or1k instructions are always 32 bits. */
 #define	OPENRISC_INSN_SIZE		4
 
+/* or1k nop instruction code */
+#define OPENRISC_INSN_NOP     0x15000000U
+
 #endif /* __ASM_OPENRISC_INSN_DEF_H */
diff --git a/arch/openrisc/include/asm/jump_label.h b/arch/openrisc/include/asm/jump_label.h
new file mode 100644
index 000000000000..3ec0f4e19f9c
--- /dev/null
+++ b/arch/openrisc/include/asm/jump_label.h
@@ -0,0 +1,72 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2025 Chen Miao
+ *
+ * Based on arch/arm/include/asm/jump_label.h
+ */
+#ifndef __ASM_OPENRISC_JUMP_LABEL_H
+#define __ASM_OPENRISC_JUMP_LABEL_H
+
+#ifndef __ASSEMBLER__
+
+#include <linux/types.h>
+#include <asm/insn-def.h>
+
+#define HAVE_JUMP_LABEL_BATCH
+
+#define JUMP_LABEL_NOP_SIZE OPENRISC_INSN_SIZE
+
+/**
+ * JUMP_TABLE_ENTRY - Create a jump table entry
+ * @key: Jump key identifier (typically a symbol address)
+ * @label: Target label address
+ *
+ * This macro creates a jump table entry in the dedicated kernel section (__jump_table).
+ * Each entry contains the following information:
+ * 		Offset from current instruction to jump instruction (1b - .)
+ * 		Offset from current instruction to target label (label - .)
+ * 		Offset from current instruction to key identifier (key - .)
+ */
+#define JUMP_TABLE_ENTRY(key, label)			\
+	".pushsection	__jump_table, \"aw\"	\n\t"	\
+	".align 	4 			\n\t"	\
+	".long 		1b - ., " label " - .	\n\t"	\
+	".long 		" key " - . 		\n\t"	\
+	".popsection				\n\t"
+
+#define ARCH_STATIC_BRANCH_ASM(key, label)		\
+	".align		4			\n\t"	\
+	"1: l.nop				\n\t"	\
+	"    l.nop				\n\t"	\
+	JUMP_TABLE_ENTRY(key, label)
+
+static __always_inline bool arch_static_branch(struct static_key *const key,
+					       const bool branch)
+{
+	asm goto (ARCH_STATIC_BRANCH_ASM("%0", "%l[l_yes]")
+		  ::"i"(&((char *)key)[branch])::l_yes);
+
+	return false;
+l_yes:
+	return true;
+}
+
+#define ARCH_STATIC_BRANCH_JUMP_ASM(key, label)		\
+	".align		4			\n\t"	\
+	"1: l.j	" label "			\n\t"	\
+	"    l.nop				\n\t"	\
+	JUMP_TABLE_ENTRY(key, label)
+
+static __always_inline bool
+arch_static_branch_jump(struct static_key *const key, const bool branch)
+{
+	asm goto (ARCH_STATIC_BRANCH_JUMP_ASM("%0", "%l[l_yes]")
+		  ::"i"(&((char *)key)[branch])::l_yes);
+
+	return false;
+l_yes:
+	return true;
+}
+
+#endif /* __ASSEMBLER__ */
+#endif /* __ASM_OPENRISC_JUMP_LABEL_H */