This implements the runtime constant infrastructure for x86, 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/x86/include/asm/runtime-const.h | 61 ++++++++++++++++++++++++++++
arch/x86/kernel/vmlinux.lds.S | 3 ++
2 files changed, 64 insertions(+)
create mode 100644 arch/x86/include/asm/runtime-const.h
diff --git a/arch/x86/include/asm/runtime-const.h b/arch/x86/include/asm/runtime-const.h
new file mode 100644
index 000000000000..24e3a53ca255
--- /dev/null
+++ b/arch/x86/include/asm/runtime-const.h
@@ -0,0 +1,61 @@
+/* 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("mov %1,%0\n1:\n" \
+ ".pushsection runtime_ptr_" #sym ",\"a\"\n\t" \
+ ".long 1b - %c2 - .\n\t" \
+ ".popsection" \
+ :"=r" (__ret) \
+ :"i" ((unsigned long)0x0123456789abcdefull), \
+ "i" (sizeof(long))); \
+ __ret; })
+
+// The 'typeof' will create at _least_ a 32-bit type, but
+// will happily also take a bigger type and the 'shrl' will
+// clear the upper bits
+#define runtime_const_shift_right_32(val, sym) ({ \
+ typeof(0u+(val)) __ret = (val); \
+ asm_inline("shrl $12,%k0\n1:\n" \
+ ".pushsection runtime_shift_" #sym ",\"a\"\n\t" \
+ ".long 1b - 1 - .\n\t" \
+ ".popsection" \
+ :"+r" (__ret)); \
+ __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)
+
+/*
+ * The text patching is trivial - you can only do this at init time,
+ * when the text section hasn't been marked RO, and before the text
+ * has ever been executed.
+ */
+static inline void __runtime_fixup_ptr(void *where, unsigned long val)
+{
+ *(unsigned long *)where = val;
+}
+
+static inline void __runtime_fixup_shift(void *where, unsigned long val)
+{
+ *(unsigned char *)where = val;
+}
+
+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/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 3509afc6a672..6e73403e874f 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -357,6 +357,9 @@ SECTIONS
PERCPU_SECTION(INTERNODE_CACHE_BYTES)
#endif
+ RUNTIME_CONST(shift, d_hash_shift)
+ RUNTIME_CONST(ptr, dentry_hashtable)
+
. = ALIGN(PAGE_SIZE);
/* freed after init ends here */
--
2.45.1.209.gc6f12300df
