xtensa: implement jump_label support

Use 3-byte 'nop' and 'j' instructions that are always present. Don't let
assembler mark a spot right after patchable 'j' instruction as
unreachable and later put literals or padding bytes there. Add separate
implementations of patch_text for SMP and UP cases, avoiding use of
atomics on UP.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

1 files changed, 65 insertions, 0 deletions

diff --git a/arch/xtensa/include/asm/jump_label.h b/arch/xtensa/include/asm/jump_label.h
new file mode 100644
index 000000000000..c812bf85021c
--- /dev/null
+++ b/arch/xtensa/include/asm/jump_label.h
@@ -0,0 +1,65 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (C) 2018 Cadence Design Systems Inc. */
+
+#ifndef _ASM_XTENSA_JUMP_LABEL_H
+#define _ASM_XTENSA_JUMP_LABEL_H
+
+#ifndef __ASSEMBLY__
+
+#include <linux/types.h>
+
+#define JUMP_LABEL_NOP_SIZE 3
+
+static __always_inline bool arch_static_branch(struct static_key *key,
+					       bool branch)
+{
+	asm_volatile_goto("1:\n\t"
+			  "_nop\n\t"
+			  ".pushsection __jump_table,  \"aw\"\n\t"
+			  ".word 1b, %l[l_yes], %c0\n\t"
+			  ".popsection\n\t"
+			  : :  "i" (&((char *)key)[branch]) :  : l_yes);
+
+	return false;
+l_yes:
+	return true;
+}
+
+static __always_inline bool arch_static_branch_jump(struct static_key *key,
+						    bool branch)
+{
+	/*
+	 * Xtensa assembler will mark certain points in the code
+	 * as unreachable, so that later assembler or linker relaxation
+	 * passes could use them. A spot right after the J instruction
+	 * is one such point. Assembler and/or linker may insert padding
+	 * or literals here, breaking code flow in case the J instruction
+	 * is later replaced with NOP. Put a label right after the J to
+	 * make it reachable and wrap both into a no-transform block
+	 * to avoid any assembler interference with this.
+	 */
+	asm_volatile_goto("1:\n\t"
+			  ".begin no-transform\n\t"
+			  "_j %l[l_yes]\n\t"
+			  "2:\n\t"
+			  ".end no-transform\n\t"
+			  ".pushsection __jump_table,  \"aw\"\n\t"
+			  ".word 1b, %l[l_yes], %c0\n\t"
+			  ".popsection\n\t"
+			  : :  "i" (&((char *)key)[branch]) :  : l_yes);
+
+	return false;
+l_yes:
+	return true;
+}
+
+typedef u32 jump_label_t;
+
+struct jump_entry {
+	jump_label_t code;
+	jump_label_t target;
+	jump_label_t key;
+};
+
+#endif  /* __ASSEMBLY__ */
+#endif