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runtime constants: add x86 architecture support

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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@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2024-06-10 12:32:14 -07:00
parent e78298556e
commit e3c92e8171
2 changed files with 64 additions and 0 deletions
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61
arch/x86/include/asm/runtime-const.h Normal file
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@ -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

3
arch/x86/kernel/vmlinux.lds.S
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@ -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 */