root/arch/x86/lib/memset_64.S

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /* Copyright 2002 Andi Kleen, SuSE Labs */
   3 
   4 #include <linux/linkage.h>
   5 #include <asm/cpufeatures.h>
   6 #include <asm/alternative-asm.h>
   7 #include <asm/export.h>
   8 
   9 .weak memset
  10 
  11 /*
  12  * ISO C memset - set a memory block to a byte value. This function uses fast
  13  * string to get better performance than the original function. The code is
  14  * simpler and shorter than the original function as well.
  15  *
  16  * rdi   destination
  17  * rsi   value (char)
  18  * rdx   count (bytes)
  19  *
  20  * rax   original destination
  21  */
  22 ENTRY(memset)
  23 ENTRY(__memset)
  24         /*
  25          * Some CPUs support enhanced REP MOVSB/STOSB feature. It is recommended
  26          * to use it when possible. If not available, use fast string instructions.
  27          *
  28          * Otherwise, use original memset function.
  29          */
  30         ALTERNATIVE_2 "jmp memset_orig", "", X86_FEATURE_REP_GOOD, \
  31                       "jmp memset_erms", X86_FEATURE_ERMS
  32 
  33         movq %rdi,%r9
  34         movq %rdx,%rcx
  35         andl $7,%edx
  36         shrq $3,%rcx
  37         /* expand byte value  */
  38         movzbl %sil,%esi
  39         movabs $0x0101010101010101,%rax
  40         imulq %rsi,%rax
  41         rep stosq
  42         movl %edx,%ecx
  43         rep stosb
  44         movq %r9,%rax
  45         ret
  46 ENDPROC(memset)
  47 ENDPROC(__memset)
  48 EXPORT_SYMBOL(memset)
  49 EXPORT_SYMBOL(__memset)
  50 
  51 /*
  52  * ISO C memset - set a memory block to a byte value. This function uses
  53  * enhanced rep stosb to override the fast string function.
  54  * The code is simpler and shorter than the fast string function as well.
  55  *
  56  * rdi   destination
  57  * rsi   value (char)
  58  * rdx   count (bytes)
  59  *
  60  * rax   original destination
  61  */
  62 ENTRY(memset_erms)
  63         movq %rdi,%r9
  64         movb %sil,%al
  65         movq %rdx,%rcx
  66         rep stosb
  67         movq %r9,%rax
  68         ret
  69 ENDPROC(memset_erms)
  70 
  71 ENTRY(memset_orig)
  72         movq %rdi,%r10
  73 
  74         /* expand byte value  */
  75         movzbl %sil,%ecx
  76         movabs $0x0101010101010101,%rax
  77         imulq  %rcx,%rax
  78 
  79         /* align dst */
  80         movl  %edi,%r9d
  81         andl  $7,%r9d
  82         jnz  .Lbad_alignment
  83 .Lafter_bad_alignment:
  84 
  85         movq  %rdx,%rcx
  86         shrq  $6,%rcx
  87         jz       .Lhandle_tail
  88 
  89         .p2align 4
  90 .Lloop_64:
  91         decq  %rcx
  92         movq  %rax,(%rdi)
  93         movq  %rax,8(%rdi)
  94         movq  %rax,16(%rdi)
  95         movq  %rax,24(%rdi)
  96         movq  %rax,32(%rdi)
  97         movq  %rax,40(%rdi)
  98         movq  %rax,48(%rdi)
  99         movq  %rax,56(%rdi)
 100         leaq  64(%rdi),%rdi
 101         jnz    .Lloop_64
 102 
 103         /* Handle tail in loops. The loops should be faster than hard
 104            to predict jump tables. */
 105         .p2align 4
 106 .Lhandle_tail:
 107         movl    %edx,%ecx
 108         andl    $63&(~7),%ecx
 109         jz              .Lhandle_7
 110         shrl    $3,%ecx
 111         .p2align 4
 112 .Lloop_8:
 113         decl   %ecx
 114         movq  %rax,(%rdi)
 115         leaq  8(%rdi),%rdi
 116         jnz    .Lloop_8
 117 
 118 .Lhandle_7:
 119         andl    $7,%edx
 120         jz      .Lende
 121         .p2align 4
 122 .Lloop_1:
 123         decl    %edx
 124         movb    %al,(%rdi)
 125         leaq    1(%rdi),%rdi
 126         jnz     .Lloop_1
 127 
 128 .Lende:
 129         movq    %r10,%rax
 130         ret
 131 
 132 .Lbad_alignment:
 133         cmpq $7,%rdx
 134         jbe     .Lhandle_7
 135         movq %rax,(%rdi)        /* unaligned store */
 136         movq $8,%r8
 137         subq %r9,%r8
 138         addq %r8,%rdi
 139         subq %r8,%rdx
 140         jmp .Lafter_bad_alignment
 141 .Lfinal:
 142 ENDPROC(memset_orig)