On Sat, 8 Jun 2024 at 13:55, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> Think of this patch mostly as a "look, adding another architecture
> isn't *that* hard - even if the constant value is spread out in the
> instructions".
.. and here's a version that actually works. It wasn't that bad.
Or rather, it wouldn't have been that bad had I not spent *ages*
debugging a stupid cut-and-paste error where I instead of writing
words 0..3 of the 64-bit large constant generation, wrote words 0..2
and then overwrote word 2 (again) with the data that should have gone
into word 3. Causing the top 32 bits to be all wonky. Oops. Literally.
That stupid typo caused like two hours of wasted time.
But anyway, this patch actually works for me. It still doesn't do any
I$/D$ flushing, because it's not needed in practice, but it *should*
probably do that.
Linus
From 887821e1cf32c505d2bc9fb9dcee45cf1e2f65e5 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Date: Sat, 8 Jun 2024 13:22:31 -0700
Subject: [PATCH] arm64: add 'runtime const' support
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..ab5f98bc942e
--- /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("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("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, value) do { \
+ extern s32 __start_runtime_##type##_##sym[]; \
+ extern s32 __stop_runtime_##type##_##sym[]; \
+ runtime_const_fixup(__runtime_fixup_##type, \
+ (unsigned long)(value), \
+ __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
