[BACK]Return to realprot.S CVS log [TXT][DIR] Up to [cvs.NetBSD.org] / src / sys / arch / i386 / stand / lib

Please note that diffs are not public domain; they are subject to the copyright notices on the relevant files.

Diff for /src/sys/arch/i386/stand/lib/realprot.S between version 1.2.2.3 and 1.2.2.4

version 1.2.2.3, 2004/09/21 13:17:11 version 1.2.2.4, 2005/11/10 13:56:54
Line 188  ENTRY(real_to_prot)
Line 188  ENTRY(real_to_prot)
  * Based on the descripton in section 14.5 of the 80386 Programmer's   * Based on the descripton in section 14.5 of the 80386 Programmer's
  * reference book.   * reference book.
  */   */
   /*
    * EPIA_HACK
    *
    * VIA C3 processors don't seem to correctly switch back to executing
    * 16 bit code after the switch to real mode and subsequent jump.
    *
    * It is speculated that the CPU is prefetching and decoding branch
    * targets and not invalidating this buffer on the long jump.
    *
    * The precise reason for this hack working is still unknown, but
    * it was determined experimentally on two theories:
    * 1) Flush the pipeline with NOPs
    * 2) call/ret after the return from prot_to_real seems to improve matters,
    *    perhaps by making more work for the branch prediction/prefetch logic.
    *
    * Neither of these individually are effective, but this combination is
    * determined experimentally to be sufficient.
    */
 ENTRY(prot_to_real)  ENTRY(prot_to_real)
   #ifdef EPIA_HACK
           .code32
           call prot_to_real_main
           .code16
           call epia_nops
           retl
   
   prot_to_real_main:
   #endif
         .code32          .code32
         pushl   %eax          pushl   %eax
   
Line 197  ENTRY(prot_to_real)
Line 224  ENTRY(prot_to_real)
          * Otherwise the control bits don't get changed.           * Otherwise the control bits don't get changed.
          * The correct base addresses are loaded later.           * The correct base addresses are loaded later.
          */           */
         movw    $bootrealdata, %ax          movw    $bootrealdata, %ax
         movw    %ax, %ds          movw    %ax, %ds
         movw    %ax, %es          movw    %ax, %es
         movw    %ax, %ss          movw    %ax, %ss
Line 240  xreal:
Line 267  xreal:
         jne     1f          jne     1f
         pop     %bp          pop     %bp
   
   #ifdef EPIA_HACK
           call epia_nops
   #endif
   
         sti          sti
         popl    %eax          popl    %eax
         retl          retl
Line 258  xreal:
Line 289  xreal:
 dump_eax_buff:  dump_eax_buff:
         . = . + 16          . = . + 16
   
   #ifdef EPIA_HACK
   epia_nops:
           .code16
           nop
           nop
           nop
           nop
           nop
           nop
           ret
   #endif
   
 /* vtophys(void *)  /* vtophys(void *)
  * convert boot time 'linear' address to a physical one   * convert boot time 'linear' address to a physical one
  */   */
Legend:
Removed from v.1.2.2.3  
changed lines
  Added in v.1.2.2.4
CVSweb <webmaster@jp.NetBSD.org>