LXR linux/arch/x86/lib/clear_page

   1#include <linux/linkage.h>
   2#include <asm/dwarf2.h>
   3#include <asm/alternative-asm.h>
   4
   5/*
   6 * Zero a page.         
   7 * rdi  page
   8 */                     
   9ENTRY(clear_page_c)
  10        CFI_STARTPROC
  11        movl $4096/8,%ecx
  12        xorl %eax,%eax
  13        rep stosq
  14        ret
  15        CFI_ENDPROC
  16ENDPROC(clear_page_c)
  17
  18ENTRY(clear_page_c_e)
  19        CFI_STARTPROC
  20        movl $4096,%ecx
  21        xorl %eax,%eax
  22        rep stosb
  23        ret
  24        CFI_ENDPROC
  25ENDPROC(clear_page_c_e)
  26
  27ENTRY(clear_page)
  28        CFI_STARTPROC
  29        xorl   %eax,%eax
  30        movl   $4096/64,%ecx
  31        .p2align 4
  32.Lloop:
  33        decl    %ecx
  34#define PUT(x) movq %rax,x*8(%rdi)
  35        movq %rax,(%rdi)
  36        PUT(1)
  37        PUT(2)
  38        PUT(3)
  39        PUT(4)
  40        PUT(5)
  41        PUT(6)
  42        PUT(7)
  43        leaq    64(%rdi),%rdi
  44        jnz     .Lloop
  45        nop
  46        ret
  47        CFI_ENDPROC
  48.Lclear_page_end:
  49ENDPROC(clear_page)
  50
  51        /*
  52         * Some CPUs support enhanced REP MOVSB/STOSB instructions.
  53         * It is recommended to use this when possible.
  54         * If enhanced REP MOVSB/STOSB is not available, try to use fast string.
  55         * Otherwise, use original function.
  56         *
  57         */
  58
  59#include <asm/cpufeature.h>
  60
  61        .section .altinstr_replacement,"ax"
  621:      .byte 0xeb                                      /* jmp <disp8> */
  63        .byte (clear_page_c - clear_page) - (2f - 1b)   /* offset */
  642:      .byte 0xeb                                      /* jmp <disp8> */
  65        .byte (clear_page_c_e - clear_page) - (3f - 2b) /* offset */
  663:
  67        .previous
  68        .section .altinstructions,"a"
  69        altinstruction_entry clear_page,1b,X86_FEATURE_REP_GOOD,\
  70                             .Lclear_page_end-clear_page, 2b-1b
  71        altinstruction_entry clear_page,2b,X86_FEATURE_ERMS,   \
  72                             .Lclear_page_end-clear_page,3b-2b
  73        .previous
  74