Module Name: src
Committed By: riastradh
Date: Sun Dec 19 01:44:03 UTC 2021
Modified Files:
src/sys/external/bsd/drm2/include/linux: nospec.h
Log Message:
array_index_nospec
To generate a diff of this commit:
cvs rdiff -u -r1.1 -r1.2 src/sys/external/bsd/drm2/include/linux/nospec.h
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/external/bsd/drm2/include/linux/nospec.h
diff -u src/sys/external/bsd/drm2/include/linux/nospec.h:1.1 src/sys/external/bsd/drm2/include/linux/nospec.h:1.2
--- src/sys/external/bsd/drm2/include/linux/nospec.h:1.1 Sun Dec 19 00:31:27 2021
+++ src/sys/external/bsd/drm2/include/linux/nospec.h Sun Dec 19 01:44:02 2021
@@ -0,0 +1,70 @@
+/* $NetBSD: nospec.h,v 1.2 2021/12/19 01:44:02 riastradh Exp $ */
+
+/*-
+ * Copyright (c) 2018 The NetBSD Foundation, Inc.
+ * All rights reserved.
+ *
+ * This code is derived from software contributed to The NetBSD Foundation
+ * by Taylor R. Campbell.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+ * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef _LINUX_NOSPEC_H_
+#define _LINUX_NOSPEC_H_
+
+#include <sys/param.h>
+#include <sys/types.h>
+
+/*
+ * array_index_nospec(i, n)
+ *
+ * If i < n, return i; otherwise return 0. Guarantees that
+ * speculative execution will behave the same even if the compiler
+ * can prove in the caller that i < n.
+ */
+static inline size_t
+array_index_nospec(size_t i, size_t n)
+{
+ size_t j, diff, mask;
+
+ /*
+ * Let j = i, but force the compiler to assume nothing about
+ * the value of j by issuing an asm block that is tagged as
+ * reading from and writing to j but actually does nothing.
+ */
+ j = i;
+ asm volatile ("" : "=r"(j) : "r"(j));
+
+ /* If i >= n, then diff has the high bit set; otherwise clear. */
+ diff = n - 1 - j;
+
+ /*
+ * If i >= n so that diff's high bit is set, mask = 0;
+ * otherwise mask = -1 = ~0.
+ */
+ mask = (diff >> (NBBY*sizeof(diff) - 1)) - 1;
+
+ return i & mask;
+}
+
+#endif /* _LINUX_NOSPEC_H_ */
