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Minimum version of binutils required to compile the kernel is 2.25. This version correctly handles the "rep" prefixes, 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 "rep; insn" (or its alternate "rep\n\tinsn" form) 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 "rep" prefixes. Trying to assemble e.g. "rep addl %eax, %ebx" results in: Error: invalid instruction `add' after `rep' Signed-off-by: Uros Bizjak <ubizjak@gmail.com> Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Brian Gerst <brgerst@gmail.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Juergen Gross <jgross@suse.com> Cc: Kees Cook <keescook@chromium.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Martin Mares <mj@ucw.cz> Cc: Peter Zijlstra <peterz@infradead.org> Link: https://lore.kernel.org/r/20250418071437.4144391-1-ubizjak@gmail.com
81 lines
1.9 KiB
C
81 lines
1.9 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* This provides an optimized implementation of memcpy, and a simplified
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* implementation of memset and memmove. These are used here because the
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* standard kernel runtime versions are not yet available and we don't
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* trust the gcc built-in implementations as they may do unexpected things
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* (e.g. FPU ops) in the minimal decompression stub execution environment.
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*/
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#include "error.h"
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#include "../string.c"
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#ifdef CONFIG_X86_32
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static void *____memcpy(void *dest, const void *src, size_t n)
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{
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int d0, d1, d2;
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asm volatile(
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"rep movsl\n\t"
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"movl %4,%%ecx\n\t"
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"rep movsb"
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: "=&c" (d0), "=&D" (d1), "=&S" (d2)
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: "0" (n >> 2), "g" (n & 3), "1" (dest), "2" (src)
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: "memory");
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return dest;
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}
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#else
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static void *____memcpy(void *dest, const void *src, size_t n)
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{
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long d0, d1, d2;
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asm volatile(
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"rep movsq\n\t"
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"movq %4,%%rcx\n\t"
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"rep movsb"
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: "=&c" (d0), "=&D" (d1), "=&S" (d2)
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: "0" (n >> 3), "g" (n & 7), "1" (dest), "2" (src)
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: "memory");
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return dest;
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}
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#endif
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void *memset(void *s, int c, size_t n)
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{
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int i;
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char *ss = s;
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for (i = 0; i < n; i++)
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ss[i] = c;
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return s;
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}
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void *memmove(void *dest, const void *src, size_t n)
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{
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unsigned char *d = dest;
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const unsigned char *s = src;
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if (d <= s || d - s >= n)
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return ____memcpy(dest, src, n);
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while (n-- > 0)
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d[n] = s[n];
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return dest;
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}
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/* Detect and warn about potential overlaps, but handle them with memmove. */
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void *memcpy(void *dest, const void *src, size_t n)
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{
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if (dest > src && dest - src < n) {
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warn("Avoiding potentially unsafe overlapping memcpy()!");
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return memmove(dest, src, n);
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}
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return ____memcpy(dest, src, n);
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}
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#ifdef CONFIG_KASAN
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extern void *__memset(void *s, int c, size_t n) __alias(memset);
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extern void *__memmove(void *dest, const void *src, size_t n) __alias(memmove);
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extern void *__memcpy(void *dest, const void *src, size_t n) __alias(memcpy);
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#endif
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