Re: [PATCH] x86/boot: Fix edd=off to skip mbr

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

On 10/13/25 11:11 PM, Jason Andryuk wrote:

> When the fixes commit re-arranged the code, it made edd=off jump to the
> mbr code instead of returning from the function.  Previously edd_done
> was immediately before ret and skipped the MBR check.
>
> Replace edd_done with .Ledd_mbr_sig for the start of the MBR checking,
> and replace .Ledd_mbr_sig_skip with .Ledd_done to exit from the function.
>
> edd=off jumps to .Ledd_done to return from the function, and internal
> jumps go to .Ledd_mbr_sig to check edd=skipmbr.
>
> Fixes: 5ec164fd61bd ("x86/boot: re-arrange how/when we do disk I/O")
> Signed-off-by: Jason Andryuk <jason.andryuk@xxxxxxx>
>     
Release-Acked-By: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>

Thanks.

~ Oleksii

> ---
>  xen/arch/x86/boot/edd.S | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/xen/arch/x86/boot/edd.S b/xen/arch/x86/boot/edd.S
> index 3df712bce1..02437511b2 100644
> --- a/xen/arch/x86/boot/edd.S
> +++ b/xen/arch/x86/boot/edd.S
> @@ -25,7 +25,7 @@
>  
>  get_edd:
>          cmpb    $2, bootsym(opt_edd)            # edd=off ?
> -        je      edd_done
> +        je      .Ledd_done
>  
>  # Do the BIOS Enhanced Disk Drive calls
>  # This consists of two calls:
> @@ -48,7 +48,7 @@ edd_check_ext:
>          movb    $0x41, %ah                      # 0x41 Check Extensions Present
>          movw    $0x55AA, %bx                    # magic
>          int     $0x13                           # make the call
> -        jc      edd_done                        # no more BIOS devices
> +        jc      .Ledd_mbr_sig                   # no more BIOS devices
>  
>          cmpw    $0xAA55, %bx                    # is magic right?
>          jne     edd_next                        # nope, next...
> @@ -96,13 +96,13 @@ edd_legacy_done:
>  
>  edd_next:
>          incb    %dl                             # increment to next device
> -        jz      edd_done
> +        jz      .Ledd_mbr_sig
>          cmpb    $EDD_INFO_MAX,bootsym(boot_edd_info_nr)
>          jb      edd_check_ext
>  
> -edd_done:
> +.Ledd_mbr_sig:
>          cmpb    $1, bootsym(opt_edd)            # edd=skipmbr ?
> -        je      .Ledd_mbr_sig_skip
> +        je      .Ledd_done
>  
>  # Read the first sector of each BIOS disk device and store the 4-byte signature
>  .Ledd_mbr_sig_start:
> @@ -160,7 +160,7 @@ edd_done:
>          jb      .Ledd_mbr_sig_read
>  .Ledd_mbr_sig_done:
>          popw    %es
> -.Ledd_mbr_sig_skip:
> +.Ledd_done:
>          ret
>  
>  GLOBAL(boot_edd_info_nr)
>