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