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023f3290b0
Minimum version of binutils required to compile the kernel is 2.25. This version correctly handles the "lock" prefix, so it is possible to remove the semicolon, which was used to support ancient versions of GNU as. Due to the semicolon, the compiler considers "lock; insn" as two separate instructions. Removing the semicolon makes asm length calculations more accurate, consequently making scheduling and inlining decisions of the compiler more accurate. Removing the semicolon also enables assembler checks involving lock prefix. Trying to assemble e.g. "lock andl %eax, %ebx" results in: Error: expecting lockable instruction after `lock' Signed-off-by: Uros Bizjak <ubizjak@gmail.com> Signed-off-by: Ingo Molnar <mingo@kernel.org> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20250228085149.2478245-1-ubizjak@gmail.com
248 lines
7.3 KiB
C
248 lines
7.3 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef ASM_X86_CMPXCHG_H
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#define ASM_X86_CMPXCHG_H
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#include <linux/compiler.h>
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#include <asm/cpufeatures.h>
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#include <asm/alternative.h> /* Provides LOCK_PREFIX */
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/*
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* Non-existent functions to indicate usage errors at link time
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* (or compile-time if the compiler implements __compiletime_error().
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*/
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extern void __xchg_wrong_size(void)
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__compiletime_error("Bad argument size for xchg");
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extern void __cmpxchg_wrong_size(void)
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__compiletime_error("Bad argument size for cmpxchg");
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extern void __xadd_wrong_size(void)
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__compiletime_error("Bad argument size for xadd");
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extern void __add_wrong_size(void)
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__compiletime_error("Bad argument size for add");
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/*
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* Constants for operation sizes. On 32-bit, the 64-bit size it set to
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* -1 because sizeof will never return -1, thereby making those switch
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* case statements guaranteed dead code which the compiler will
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* eliminate, and allowing the "missing symbol in the default case" to
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* indicate a usage error.
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*/
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#define __X86_CASE_B 1
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#define __X86_CASE_W 2
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#define __X86_CASE_L 4
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#ifdef CONFIG_64BIT
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#define __X86_CASE_Q 8
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#else
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#define __X86_CASE_Q -1 /* sizeof will never return -1 */
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#endif
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/*
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* An exchange-type operation, which takes a value and a pointer, and
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* returns the old value.
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*/
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#define __xchg_op(ptr, arg, op, lock) \
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({ \
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__typeof__ (*(ptr)) __ret = (arg); \
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switch (sizeof(*(ptr))) { \
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case __X86_CASE_B: \
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asm volatile (lock #op "b %b0, %1\n" \
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: "+q" (__ret), "+m" (*(ptr)) \
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: : "memory", "cc"); \
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break; \
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case __X86_CASE_W: \
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asm volatile (lock #op "w %w0, %1\n" \
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: "+r" (__ret), "+m" (*(ptr)) \
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: : "memory", "cc"); \
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break; \
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case __X86_CASE_L: \
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asm volatile (lock #op "l %0, %1\n" \
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: "+r" (__ret), "+m" (*(ptr)) \
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: : "memory", "cc"); \
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break; \
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case __X86_CASE_Q: \
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asm volatile (lock #op "q %q0, %1\n" \
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: "+r" (__ret), "+m" (*(ptr)) \
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: : "memory", "cc"); \
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break; \
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default: \
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__ ## op ## _wrong_size(); \
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} \
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__ret; \
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})
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/*
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* Note: no "lock" prefix even on SMP: xchg always implies lock anyway.
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* Since this is generally used to protect other memory information, we
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* use "asm volatile" and "memory" clobbers to prevent gcc from moving
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* information around.
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*/
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#define arch_xchg(ptr, v) __xchg_op((ptr), (v), xchg, "")
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/*
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* Atomic compare and exchange. Compare OLD with MEM, if identical,
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* store NEW in MEM. Return the initial value in MEM. Success is
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* indicated by comparing RETURN with OLD.
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*/
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#define __raw_cmpxchg(ptr, old, new, size, lock) \
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({ \
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__typeof__(*(ptr)) __ret; \
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__typeof__(*(ptr)) __old = (old); \
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__typeof__(*(ptr)) __new = (new); \
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switch (size) { \
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case __X86_CASE_B: \
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{ \
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volatile u8 *__ptr = (volatile u8 *)(ptr); \
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asm volatile(lock "cmpxchgb %2,%1" \
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: "=a" (__ret), "+m" (*__ptr) \
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: "q" (__new), "0" (__old) \
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: "memory"); \
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break; \
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} \
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case __X86_CASE_W: \
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{ \
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volatile u16 *__ptr = (volatile u16 *)(ptr); \
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asm volatile(lock "cmpxchgw %2,%1" \
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: "=a" (__ret), "+m" (*__ptr) \
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: "r" (__new), "0" (__old) \
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: "memory"); \
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break; \
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} \
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case __X86_CASE_L: \
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{ \
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volatile u32 *__ptr = (volatile u32 *)(ptr); \
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asm volatile(lock "cmpxchgl %2,%1" \
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: "=a" (__ret), "+m" (*__ptr) \
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: "r" (__new), "0" (__old) \
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: "memory"); \
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break; \
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} \
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case __X86_CASE_Q: \
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{ \
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volatile u64 *__ptr = (volatile u64 *)(ptr); \
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asm volatile(lock "cmpxchgq %2,%1" \
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: "=a" (__ret), "+m" (*__ptr) \
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: "r" (__new), "0" (__old) \
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: "memory"); \
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break; \
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} \
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default: \
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__cmpxchg_wrong_size(); \
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} \
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__ret; \
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})
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#define __cmpxchg(ptr, old, new, size) \
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__raw_cmpxchg((ptr), (old), (new), (size), LOCK_PREFIX)
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#define __sync_cmpxchg(ptr, old, new, size) \
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__raw_cmpxchg((ptr), (old), (new), (size), "lock ")
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#define __cmpxchg_local(ptr, old, new, size) \
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__raw_cmpxchg((ptr), (old), (new), (size), "")
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#ifdef CONFIG_X86_32
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# include <asm/cmpxchg_32.h>
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#else
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# include <asm/cmpxchg_64.h>
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#endif
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#define arch_cmpxchg(ptr, old, new) \
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__cmpxchg(ptr, old, new, sizeof(*(ptr)))
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#define arch_sync_cmpxchg(ptr, old, new) \
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__sync_cmpxchg(ptr, old, new, sizeof(*(ptr)))
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#define arch_cmpxchg_local(ptr, old, new) \
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__cmpxchg_local(ptr, old, new, sizeof(*(ptr)))
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#define __raw_try_cmpxchg(_ptr, _pold, _new, size, lock) \
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({ \
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bool success; \
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__typeof__(_ptr) _old = (__typeof__(_ptr))(_pold); \
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__typeof__(*(_ptr)) __old = *_old; \
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__typeof__(*(_ptr)) __new = (_new); \
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switch (size) { \
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case __X86_CASE_B: \
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{ \
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volatile u8 *__ptr = (volatile u8 *)(_ptr); \
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asm volatile(lock "cmpxchgb %[new], %[ptr]" \
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CC_SET(z) \
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: CC_OUT(z) (success), \
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[ptr] "+m" (*__ptr), \
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[old] "+a" (__old) \
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: [new] "q" (__new) \
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: "memory"); \
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break; \
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} \
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case __X86_CASE_W: \
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{ \
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volatile u16 *__ptr = (volatile u16 *)(_ptr); \
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asm volatile(lock "cmpxchgw %[new], %[ptr]" \
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CC_SET(z) \
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: CC_OUT(z) (success), \
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[ptr] "+m" (*__ptr), \
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[old] "+a" (__old) \
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: [new] "r" (__new) \
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: "memory"); \
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break; \
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} \
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case __X86_CASE_L: \
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{ \
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volatile u32 *__ptr = (volatile u32 *)(_ptr); \
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asm volatile(lock "cmpxchgl %[new], %[ptr]" \
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CC_SET(z) \
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: CC_OUT(z) (success), \
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[ptr] "+m" (*__ptr), \
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[old] "+a" (__old) \
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: [new] "r" (__new) \
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: "memory"); \
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break; \
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} \
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case __X86_CASE_Q: \
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{ \
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volatile u64 *__ptr = (volatile u64 *)(_ptr); \
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asm volatile(lock "cmpxchgq %[new], %[ptr]" \
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CC_SET(z) \
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: CC_OUT(z) (success), \
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[ptr] "+m" (*__ptr), \
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[old] "+a" (__old) \
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: [new] "r" (__new) \
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: "memory"); \
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break; \
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} \
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default: \
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__cmpxchg_wrong_size(); \
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} \
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if (unlikely(!success)) \
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*_old = __old; \
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likely(success); \
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})
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#define __try_cmpxchg(ptr, pold, new, size) \
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__raw_try_cmpxchg((ptr), (pold), (new), (size), LOCK_PREFIX)
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#define __sync_try_cmpxchg(ptr, pold, new, size) \
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__raw_try_cmpxchg((ptr), (pold), (new), (size), "lock ")
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#define __try_cmpxchg_local(ptr, pold, new, size) \
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__raw_try_cmpxchg((ptr), (pold), (new), (size), "")
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#define arch_try_cmpxchg(ptr, pold, new) \
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__try_cmpxchg((ptr), (pold), (new), sizeof(*(ptr)))
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#define arch_sync_try_cmpxchg(ptr, pold, new) \
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__sync_try_cmpxchg((ptr), (pold), (new), sizeof(*(ptr)))
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#define arch_try_cmpxchg_local(ptr, pold, new) \
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__try_cmpxchg_local((ptr), (pold), (new), sizeof(*(ptr)))
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/*
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* xadd() adds "inc" to "*ptr" and atomically returns the previous
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* value of "*ptr".
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*
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* xadd() is locked when multiple CPUs are online
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*/
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#define __xadd(ptr, inc, lock) __xchg_op((ptr), (inc), xadd, lock)
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#define xadd(ptr, inc) __xadd((ptr), (inc), LOCK_PREFIX)
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#endif /* ASM_X86_CMPXCHG_H */
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