aboutsummaryrefslogtreecommitdiff
path: root/arch/arc/include
diff options
context:
space:
mode:
authorEugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>2019-11-08 19:20:22 +0300
committerVineet Gupta <vgupta@synopsys.com>2019-11-08 16:14:32 -0800
commitf091d5a426447cc427680bdd3adc7773aa2867df (patch)
treee255dd3806463334c58d03aff06dee6e3b3268c3 /arch/arc/include
parent2f4ecf68a048de44d72157d637bf9cbbbdb357b0 (diff)
downloadlinux-f091d5a426447cc427680bdd3adc7773aa2867df.tar.gz
ARC: ARCv2: jump label: implement jump label patching
Implement jump label patching for ARC. Jump labels provide an interface to generate dynamic branches using self-modifying code. This allows us to implement conditional branches where changing branch direction is expensive but branch selection is basically 'free' This implementation uses 32-bit NOP and BRANCH instructions which forced to be aligned by 4 to guarantee that they don't cross L1 cache line boundary and can be update atomically. Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com> Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Diffstat (limited to 'arch/arc/include')
-rw-r--r--arch/arc/include/asm/cache.h2
-rw-r--r--arch/arc/include/asm/jump_label.h72
2 files changed, 74 insertions, 0 deletions
diff --git a/arch/arc/include/asm/cache.h b/arch/arc/include/asm/cache.h
index 918804c7c1a4..d8ece4292388 100644
--- a/arch/arc/include/asm/cache.h
+++ b/arch/arc/include/asm/cache.h
@@ -25,6 +25,8 @@
#ifndef __ASSEMBLY__
+#include <linux/build_bug.h>
+
/* Uncached access macros */
#define arc_read_uncached_32(ptr) \
({ \
diff --git a/arch/arc/include/asm/jump_label.h b/arch/arc/include/asm/jump_label.h
new file mode 100644
index 000000000000..9d9618079739
--- /dev/null
+++ b/arch/arc/include/asm/jump_label.h
@@ -0,0 +1,72 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_ARC_JUMP_LABEL_H
+#define _ASM_ARC_JUMP_LABEL_H
+
+#ifndef __ASSEMBLY__
+
+#include <linux/stringify.h>
+#include <linux/types.h>
+
+#define JUMP_LABEL_NOP_SIZE 4
+
+/*
+ * NOTE about '.balign 4':
+ *
+ * To make atomic update of patched instruction available we need to guarantee
+ * that this instruction doesn't cross L1 cache line boundary.
+ *
+ * As of today we simply align instruction which can be patched by 4 byte using
+ * ".balign 4" directive. In that case patched instruction is aligned with one
+ * 16-bit NOP_S if this is required.
+ * However 'align by 4' directive is much stricter than it actually required.
+ * It's enough that our 32-bit instruction don't cross L1 cache line boundary /
+ * L1 I$ fetch block boundary which can be achieved by using
+ * ".bundle_align_mode" assembler directive. That will save us from adding
+ * useless NOP_S padding in most of the cases.
+ *
+ * TODO: switch to ".bundle_align_mode" directive using whin it will be
+ * supported by ARC toolchain.
+ */
+
+static __always_inline bool arch_static_branch(struct static_key *key,
+ bool branch)
+{
+ asm_volatile_goto(".balign "__stringify(JUMP_LABEL_NOP_SIZE)" \n"
+ "1: \n"
+ "nop \n"
+ ".pushsection __jump_table, \"aw\" \n"
+ ".word 1b, %l[l_yes], %c0 \n"
+ ".popsection \n"
+ : : "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)
+{
+ asm_volatile_goto(".balign "__stringify(JUMP_LABEL_NOP_SIZE)" \n"
+ "1: \n"
+ "b %l[l_yes] \n"
+ ".pushsection __jump_table, \"aw\" \n"
+ ".word 1b, %l[l_yes], %c0 \n"
+ ".popsection \n"
+ : : "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