src/arch/x86/memset.c

   1 /* SPDX-License-Identifier: GPL-2.0-or-later */
   2
   3 /* From glibc-2.14, sysdeps/i386/memset.c */
   4
   5 #include <string.h>
   6 #include <stdint.h>
   7 #include <stdbool.h>
   8 #include <asan.h>
   9
  10 typedef uint32_t op_t;
  11
  12 void *memset(void *dstpp, int c, size_t len)
  13 {
  14         int d0;
  15         unsigned long int dstp = (unsigned long int)dstpp;
  16
  17 #if (ENV_SEPARATE_ROMSTAGE && CONFIG(ASAN_IN_ROMSTAGE)) || \
  18                 (ENV_RAMSTAGE && CONFIG(ASAN_IN_RAMSTAGE))
  19         check_memory_region((unsigned long)dstpp, len, true, _RET_IP_);
  20 #endif
  21
  22         /* This explicit register allocation improves code very much indeed. */
  23         register op_t x asm("ax");
  24
  25         x = (unsigned char)c;
  26
  27         /* Clear the direction flag, so filling will move forward.  */
  28         asm volatile("cld");
  29
  30         /* This threshold value is optimal.  */
  31         if (len >= 12) {
  32                 /* Fill X with four copies of the char we want to fill with. */
  33                 x |= (x << 8);
  34                 x |= (x << 16);
  35
  36                 /* Adjust LEN for the bytes handled in the first loop.  */
  37                 len -= (-dstp) % sizeof(op_t);
  38
  39                 /*
  40                  * There are at least some bytes to set. No need to test for
  41                  * LEN == 0 in this alignment loop.
  42                  */
  43
  44                 /* Fill bytes until DSTP is aligned on a longword boundary. */
  45                 asm volatile(
  46                         "rep\n"
  47                         "stosb" /* %0, %2, %3 */ :
  48                         "=D" (dstp), "=c" (d0) :
  49                         "0" (dstp), "1" ((-dstp) % sizeof(op_t)), "a" (x) :
  50                         "memory");
  51
  52                 /* Fill longwords.  */
  53                 asm volatile(
  54                         "rep\n"
  55                         "stosl" /* %0, %2, %3 */ :
  56                         "=D" (dstp), "=c" (d0) :
  57                         "0" (dstp), "1" (len / sizeof(op_t)), "a" (x) :
  58                         "memory");
  59                 len %= sizeof(op_t);
  60         }
  61
  62         /* Write the last few bytes. */
  63         asm volatile(
  64                 "rep\n"
  65                 "stosb" /* %0, %2, %3 */ :
  66                 "=D" (dstp), "=c" (d0) :
  67                 "0" (dstp), "1" (len), "a" (x) :
  68                 "memory");
  69
  70         return dstpp;
  71 }