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Re: [qemu-s390x] [PATCH 2/2] pc-bios/s390-ccw: zero out bss section


From: Thomas Huth
Subject: Re: [qemu-s390x] [PATCH 2/2] pc-bios/s390-ccw: zero out bss section
Date: Wed, 22 Nov 2017 17:36:03 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0

On 22.11.2017 15:26, Christian Borntraeger wrote:
> The QEMU ELF loader does not zero the bss segment.
> This resulted in several bugs, e.g. see
> 
> commit 5d739a4787a5 (s390-ccw.img: Fix sporadic errors with ccw boot image - 
> initialize css)
> commit 6a40fa2669d3 (s390-ccw.img: Initialize next_idx)
> commit 8775d91a0f42 (pc-bios/s390-ccw: Fix problem with invalid virtio-scsi 
> LUN when rebooting)
> 
> Lets fix this once and forever by letting the BIOS zero the bss itself.
> 
> Suggested-by: Alexander Graf <address@hidden>
> Signed-off-by: Christian Borntraeger <address@hidden>
> ---
>  pc-bios/s390-ccw/start.S | 30 +++++++++++++++++++++++++++---
>  1 file changed, 27 insertions(+), 3 deletions(-)
> 
> diff --git a/pc-bios/s390-ccw/start.S b/pc-bios/s390-ccw/start.S
> index 43f9bd2..eb8d024 100644
> --- a/pc-bios/s390-ccw/start.S
> +++ b/pc-bios/s390-ccw/start.S
> @@ -3,7 +3,7 @@
>   * into the pc-bios directory of qemu.
>   *
>   * Copyright (c) 2013 Alexander Graf <address@hidden>
> - * Copyright 2013 IBM Corp.
> + * Copyright IBM Corp. 2013, 2017
>   *
>   * This work is licensed under the terms of the GNU GPL, version 2 or (at
>   * your option) any later version. See the COPYING file in the top-level
> @@ -13,8 +13,32 @@
>          .globl _start
>  _start:
>  
> -larl %r15, stack + 0x8000    /* Set up stack */
> -j    main                    /* And call C */
> +     larl   %r15, stack + 0x8000     /* Set up stack */
> +
> +     /* clear bss */
> +     larl %r2, __bss_start
> +     larl %r3, _end
> +     slgr %r3, %r2           /* get sizeof bss */
> +     ltgr    %r3,%r3         /* bss emtpy? */
> +     jz      done
> +     aghi    %r3,-1
> +     srlg    %r4,%r3,8       /* how many 256 byte chunks? */
> +     ltgr    %r4,%r4
> +     lgr     %r1,%r2
> +     jz      remainder
> +loop:
> +     xc      0(256,%r1),0(%r1)
> +     la      %r1,256(%r1)
> +     brctg   %r4,loop
> +remainder:
> +     larl    %r2,memsetxc
> +     ex      %r3,0(%r2)

Wow, with EXECUTE :-)

> +done:
> +     j      main             /* And call C */
> +
> +memsetxc:
> +     xc      0(1,%r1),0(%r1)
> +
>  
>  /*
>   * void disabled_wait(void)
> 

Looks good to me:

Reviewed-by: Thomas Huth <address@hidden>



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