Re: [PATCH] THE LINUX/I386 BOOT PROTOCOL - Breaking the 256 limit (ping)

[Alon Bar-Lev <alon.barlev@gmail.com>]

Alon Bar-Lev wrote:
> H. Peter Anvin wrote:
> > Found the references.  This seems to imply that EDD overwrites the 
> > area used by LILO 22.6.1.  LILO 22.6.1 uses the new boot protocol, 
> > with the full pointer, and seems to obey the spec as far as I can read 
> > the code.  I'm going to try to run it in simulation and observe the 
> > failure that way.
> >
> > However, something is still seriously out of joint.  The EDD data 
> > actually overlays the setup code, not the bootsect code, and thus 
> > there "shouldn't" be any way that this could interfere.  My best guess 
> > at this time is that either the EDD code or LILO uses memory it's not 
> > supposed to use, and the simulation should hopefully reveal that.
> >
> > Sorry if I seem snarky on this, but if we can't get to the bottom of 
> > this we can't ever fix it.
> >
> >     -hpa
>
> I think I've found one problem... But I it should not be the major one.
> The EDD code scans the command-line as fixed string.
> What about something like the following?
>
> Best Regards,
> Alon Bar-Lev.
>
> diff -urNp linux-2.6.18-rc4-mm2/arch/i386/boot/edd.S 
> linux-2.6.18-rc4-mm2.new/arch/i386/boot/edd.S
> --- linux-2.6.18-rc4-mm2/arch/i386/boot/edd.S   2006-06-18 
> 04:49:35.000000000 +0300
> +++ linux-2.6.18-rc4-mm2.new/arch/i386/boot/edd.S       2006-08-28 
> 08:55:01.000000000 +0300
> @@ -29,6 +29,8 @@
>         movl    $(COMMAND_LINE_SIZE-7), %ecx
>  # loop through kernel command line one byte at a time
>  cl_loop:
> +       cmpb    $0,(%si)
> +       jz      done_cl
>         cmpl    $EDD_CL_EQUALS, (%si)
>         jz      found_edd_equals
>         incl    %esi

Better patch.
I've noticed that this code sets esi but then reference using si... So fixed to
use esi (It worked so far since we are in low area... But I think using the same
register type is cleaner...)

Best Regards,
Alon Bar-Lev.

diff -urNp linux-2.6.18-rc4-mm2/arch/i386/boot/edd.S linux-2.6.18-rc4-mm2.new/arch/i386/boot/edd.S
--- linux-2.6.18-rc4-mm2/arch/i386/boot/edd.S   2006-06-18 04:49:35.000000000 +0300
+++ linux-2.6.18-rc4-mm2.new/arch/i386/boot/edd.S       2006-08-28 09:34:39.000000000 +0300
@@ -29,7 +29,9 @@
        movl    $(COMMAND_LINE_SIZE-7), %ecx
 # loop through kernel command line one byte at a time
 cl_loop:
-       cmpl    $EDD_CL_EQUALS, (%si)
+       cmpb    $0,(%esi)
+       jz      done_cl
+       cmpl    $EDD_CL_EQUALS, (%esi)
        jz      found_edd_equals
        incl    %esi
        loop    cl_loop
@@ -37,9 +39,9 @@ cl_loop:
 found_edd_equals:
 # only looking at first two characters after equals
        addl    $4, %esi
-       cmpw    $EDD_CL_OFF, (%si)      # edd=of
+       cmpw    $EDD_CL_OFF, (%esi)     # edd=of
        jz      do_edd_off
-       cmpw    $EDD_CL_SKIP, (%si)     # edd=sk
+       cmpw    $EDD_CL_SKIP, (%esi)    # edd=sk
        jz      do_edd_skipmbr
        jmp     done_cl
 do_edd_skipmbr:
-
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