[PATCH 4/7] arm64: add 'runtime constant' support

[Linus Torvalds]

This implements the runtime constant infrastructure for arm64, allowing
the dcache d_hash() function to be generated using as a constant for
hash table address followed by shift by a constant of the hash index.

Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
---
 arch/arm64/include/asm/runtime-const.h | 75 ++++++++++++++++++++++++++
 arch/arm64/kernel/vmlinux.lds.S        |  3 ++
 2 files changed, 78 insertions(+)
 create mode 100644 arch/arm64/include/asm/runtime-const.h

diff --git a/arch/arm64/include/asm/runtime-const.h b/arch/arm64/include/asm/runtime-const.h
new file mode 100644
index 000000000000..02462b2cb6f9
--- /dev/null
+++ b/arch/arm64/include/asm/runtime-const.h
@@ -0,0 +1,75 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_RUNTIME_CONST_H
+#define _ASM_RUNTIME_CONST_H
+
+#define runtime_const_ptr(sym) ({				\
+	typeof(sym) __ret;					\
+	asm_inline("1:\t"					\
+		"movz %0, #0xcdef\n\t"				\
+		"movk %0, #0x89ab, lsl #16\n\t"			\
+		"movk %0, #0x4567, lsl #32\n\t"			\
+		"movk %0, #0x0123, lsl #48\n\t"			\
+		".pushsection runtime_ptr_" #sym ",\"a\"\n\t"	\
+		".long 1b - .\n\t"				\
+		".popsection"					\
+		:"=r" (__ret));					\
+	__ret; })
+
+#define runtime_const_shift_right_32(val, sym) ({		\
+	unsigned long __ret;					\
+	asm_inline("1:\t"					\
+		"lsr %w0,%w1,#12\n\t"				\
+		".pushsection runtime_shift_" #sym ",\"a\"\n\t"	\
+		".long 1b - .\n\t"				\
+		".popsection"					\
+		:"=r" (__ret)					\
+		:"r" (0u+(val)));				\
+	__ret; })
+
+#define runtime_const_init(type, sym) do {		\
+	extern s32 __start_runtime_##type##_##sym[];	\
+	extern s32 __stop_runtime_##type##_##sym[];	\
+	runtime_const_fixup(__runtime_fixup_##type,	\
+		(unsigned long)(sym), 			\
+		__start_runtime_##type##_##sym,		\
+		__stop_runtime_##type##_##sym);		\
+} while (0)
+
+// 16-bit immediate for wide move (movz and movk) in bits 5..20
+static inline void __runtime_fixup_16(unsigned int *p, unsigned int val)
+{
+	unsigned int insn = *p;
+	insn &= 0xffe0001f;
+	insn |= (val & 0xffff) << 5;
+	*p = insn;
+}
+
+static inline void __runtime_fixup_ptr(void *where, unsigned long val)
+{
+	unsigned int *p = lm_alias(where);
+	__runtime_fixup_16(p, val);
+	__runtime_fixup_16(p+1, val >> 16);
+	__runtime_fixup_16(p+2, val >> 32);
+	__runtime_fixup_16(p+3, val >> 48);
+}
+
+// Immediate value is 5 bits starting at bit #16
+static inline void __runtime_fixup_shift(void *where, unsigned long val)
+{
+	unsigned int *p = lm_alias(where);
+	unsigned int insn = *p;
+	insn &= 0xffc0ffff;
+	insn |= (val & 63) << 16;
+	*p = insn;
+}
+
+static inline void runtime_const_fixup(void (*fn)(void *, unsigned long),
+	unsigned long val, s32 *start, s32 *end)
+{
+	while (start < end) {
+		fn(*start + (void *)start, val);
+		start++;
+	}
+}
+
+#endif
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index 755a22d4f840..55a8e310ea12 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -264,6 +264,9 @@ SECTIONS
 		EXIT_DATA
 	}
 
+	RUNTIME_CONST(shift, d_hash_shift)
+	RUNTIME_CONST(ptr, dentry_hashtable)
+
 	PERCPU_SECTION(L1_CACHE_BYTES)
 	HYPERVISOR_PERCPU_SECTION
 
-- 
2.45.1.209.gc6f12300df