boot/compressed/string.c

0001 // SPDX-License-Identifier: GPL-2.0
0002 /*
0003  * This provides an optimized implementation of memcpy, and a simplified
0004  * implementation of memset and memmove. These are used here because the
0005  * standard kernel runtime versions are not yet available and we don't
0006  * trust the gcc built-in implementations as they may do unexpected things
0007  * (e.g. FPU ops) in the minimal decompression stub execution environment.
0008  */
0009 #include "error.h"
0010
0011 #include "../string.c"
0012
0013 #ifdef CONFIG_X86_32
0014 static void *____memcpy(void *dest, const void *src, size_t n)
0015 {
0016     int d0, d1, d2;
0017     asm volatile(
0018         "rep ; movsl\n\t"
0019         "movl %4,%%ecx\n\t"
0020         "rep ; movsb\n\t"
0021         : "=&c" (d0), "=&D" (d1), "=&S" (d2)
0022         : "0" (n >> 2), "g" (n & 3), "1" (dest), "2" (src)
0023         : "memory");
0024
0025     return dest;
0026 }
0027 #else
0028 static void *____memcpy(void *dest, const void *src, size_t n)
0029 {
0030     long d0, d1, d2;
0031     asm volatile(
0032         "rep ; movsq\n\t"
0033         "movq %4,%%rcx\n\t"
0034         "rep ; movsb\n\t"
0035         : "=&c" (d0), "=&D" (d1), "=&S" (d2)
0036         : "0" (n >> 3), "g" (n & 7), "1" (dest), "2" (src)
0037         : "memory");
0038
0039     return dest;
0040 }
0041 #endif
0042
0043 void *memset(void *s, int c, size_t n)
0044 {
0045     int i;
0046     char *ss = s;
0047
0048     for (i = 0; i < n; i++)
0049         ss[i] = c;
0050     return s;
0051 }
0052
0053 void *memmove(void *dest, const void *src, size_t n)
0054 {
0055     unsigned char *d = dest;
0056     const unsigned char *s = src;
0057
0058     if (d <= s || d - s >= n)
0059         return ____memcpy(dest, src, n);
0060
0061     while (n-- > 0)
0062         d[n] = s[n];
0063
0064     return dest;
0065 }
0066
0067 /* Detect and warn about potential overlaps, but handle them with memmove. */
0068 void *memcpy(void *dest, const void *src, size_t n)
0069 {
0070     if (dest > src && dest - src < n) {
0071         warn("Avoiding potentially unsafe overlapping memcpy()!");
0072         return memmove(dest, src, n);
0073     }
0074     return ____memcpy(dest, src, n);
0075 }
0076
0077 #ifdef CONFIG_KASAN
0078 extern void *__memset(void *s, int c, size_t n) __alias(memset);
0079 extern void *__memmove(void *dest, const void *src, size_t n) __alias(memmove);
0080 extern void *__memcpy(void *dest, const void *src, size_t n) __alias(memcpy);
0081 #endif