Re: install/42202 (boot installcd fails ((amd64/i386))

[Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost>]

The following reply was made to PR install/42202; it has been noted by GNATS.

From: Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost>
To: gnats-bugs%NetBSD.org@localhost, jmcneill%NetBSD.org@localhost
Cc: njoly%pasteur.fr@localhost, gnats-admin%NetBSD.org@localhost, 
netbsd-bugs%NetBSD.org@localhost,
        kosaki_kt%ybb.ne.jp@localhost, tsutsui%ceres.dti.ne.jp@localhost
Subject: Re: install/42202 (boot installcd fails ((amd64/i386))
Date: Sat, 24 Oct 2009 07:24:43 +0900

 I wrote:
 
 > The real fix is to update cdboot.S to support real <-> protect mode
 > switches provided by i386/stand/lib/realprot.S, which is already used
 > by other primary bootxx loaders.
 
 Ah, no. The problem depends on implementation of INT 13h function 42h
 (some BIOSes might handle it properly though), so we might have to
 split a large xfer within 64KB in read_sectors function.
 
 The attached dumb patch (checks and split >64KB xfers)
 seems to work around even with ~67KB /boot on my machine.
 (though I'm not familiar with x86 asm at all)
 
 ---
 Index: stand/cdboot/cdboot.S
 ===================================================================
 RCS file: /cvsroot/src/sys/arch/i386/stand/cdboot/cdboot.S,v
 retrieving revision 1.8
 diff -u -r1.8 cdboot.S
 --- stand/cdboot/cdboot.S      3 May 2008 13:07:31 -0000       1.8
 +++ stand/cdboot/cdboot.S      23 Oct 2009 22:12:50 -0000
 @@ -47,6 +47,9 @@
  #define PVD_ADDR      0x1000          /* Where Primary VD is loaded */
  #define ROOTDIR_ADDR  0x1800          /* Where Root Directory is loaded */
  #define LOADER_ADDR   SECONDARY_LOAD_ADDRESS
 +#define SEGMENT_SIZE  0x10000
 +#define MAX_NBLOCK    (SEGMENT_SIZE / BLOCK_SIZE)
 +#define NEXT_SEGMENT  (SEGMENT_SIZE >> 4)
  
  #ifdef BOOT_FROM_FAT
  #define MBR_AFTERBPB  90              /* BPB size in FAT32 partition BR */
 @@ -297,16 +300,33 @@
   */
  read_sectors:
        pusha
 -      movl    %eax, edd_lba           /* Convert LBA to segment */
        shrl    $4, %ebx
 +read_again:
 +      movl    %eax, edd_lba           /* Convert LBA to segment */
        movw    %bx, edd_segment
 +      pushl   %eax
 +      push    %bx
 +      push    %dx
 +      cmpb    $MAX_NBLOCK, %dh
 +      jle     1f
 +      movb    $MAX_NBLOCK, %dh
 +1:
        movb    %dh, edd_nsecs
        movb    boot_drive, %dl
        movw    $edd_packet, %si
 -read_again:
        movb    $0x42, %ah
        int     $0x13
 +      pop     %dx
 +      pop     %bx
 +      popl    %eax
        jc      read_fail
 +      cmpb    $MAX_NBLOCK, %dh
 +      jle     2f
 +      subb    $MAX_NBLOCK, %dh
 +      addl    $MAX_NBLOCK, %eax
 +      addw    $NEXT_SEGMENT, %bx
 +      jmp     read_again
 +2:
        popa
        ret
  read_fail:
 
 ---
 Izumi Tsutsui