runtime constants: add default dummy infrastructure

This adds the initial dummy support for 'runtime constants' for when
an architecture doesn't actually support an implementation of fixing
up said runtime constants.

This ends up being the fallback to just using the variables as regular
__ro_after_init variables, and changes the dcache d_hash() function to
use this model.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/dcache.c b/fs/dcache.c
index 8b4382f5c99d051104ec9d4b89572d805dd0ad0c..5d3a5b3156928ffa6121bfd229456887830f5a89 100644 (file)
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -35,6 +35,8 @@
 #include "internal.h"
 #include "mount.h"
 
+#include <asm/runtime-const.h>
+
 /*
  * Usage:
  * dcache->d_inode->i_lock protects:
@@ -102,7 +104,8 @@ static struct hlist_bl_head *dentry_hashtable __ro_after_init;
 
 static inline struct hlist_bl_head *d_hash(unsigned long hashlen)
 {
-       return dentry_hashtable + ((u32)hashlen >> d_hash_shift);
+       return runtime_const_ptr(dentry_hashtable) +
+               runtime_const_shift_right_32(hashlen, d_hash_shift);
 }
 
 #define IN_LOOKUP_SHIFT 10
@@ -3129,6 +3132,9 @@ static void __init dcache_init_early(void)
                                        0,
                                        0);
        d_hash_shift = 32 - d_hash_shift;
+
+       runtime_const_init(shift, d_hash_shift);
+       runtime_const_init(ptr, dentry_hashtable);
 }
 
 static void __init dcache_init(void)
@@ -3157,6 +3163,9 @@ static void __init dcache_init(void)
                                        0,
                                        0);
        d_hash_shift = 32 - d_hash_shift;
+
+       runtime_const_init(shift, d_hash_shift);
+       runtime_const_init(ptr, dentry_hashtable);
 }
 
 /* SLAB cache for __getname() consumers */

diff --git a/include/asm-generic/Kbuild b/include/asm-generic/Kbuild
index b20fa25a7e8d8e21a960e589f780eb768e5c186e..052e5c98c1055b817b47d590b8357382df7c6c24 100644 (file)
--- a/include/asm-generic/Kbuild
+++ b/include/asm-generic/Kbuild
@@ -46,6 +46,7 @@ mandatory-y += pci.h
 mandatory-y += percpu.h
 mandatory-y += pgalloc.h
 mandatory-y += preempt.h
+mandatory-y += runtime-const.h
 mandatory-y += rwonce.h
 mandatory-y += sections.h
 mandatory-y += serial.h

diff --git a/include/asm-generic/runtime-const.h b/include/asm-generic/runtime-const.h
new file mode 100644 (file)
index 0000000..6704994
--- /dev/null
+++ b/include/asm-generic/runtime-const.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_RUNTIME_CONST_H
+#define _ASM_RUNTIME_CONST_H
+
+/*
+ * This is the fallback for when the architecture doesn't
+ * support the runtime const operations.
+ *
+ * We just use the actual symbols as-is.
+ */
+#define runtime_const_ptr(sym) (sym)
+#define runtime_const_shift_right_32(val, sym) ((u32)(val)>>(sym))
+#define runtime_const_init(type,sym) do { } while (0)
+
+#endif

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 5703526d6ebf13bcca1d092edcffd0180db48bad..389a78415b9b7b3549243066aa583f17cb2984c4 100644 (file)
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -944,6 +944,14 @@
 #define CON_INITCALL                                                   \
        BOUNDED_SECTION_POST_LABEL(.con_initcall.init, __con_initcall, _start, _end)
 
+#define RUNTIME_NAME(t,x) runtime_##t##_##x
+
+#define RUNTIME_CONST(t,x)                                             \
+       . = ALIGN(8);                                                   \
+       RUNTIME_NAME(t,x) : AT(ADDR(RUNTIME_NAME(t,x)) - LOAD_OFFSET) { \
+               *(RUNTIME_NAME(t,x));                                   \
+       }
+
 /* Alignment must be consistent with (kunit_suite *) in include/kunit/test.h */
 #define KUNIT_TABLE()                                                  \
                . = ALIGN(8);                                           \