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Re: [Qemu-devel] [PATCH] pc-bios/s390-ccw: build s390 bios with -fno-zer

From: Christian Borntraeger
Subject: Re: [Qemu-devel] [PATCH] pc-bios/s390-ccw: build s390 bios with -fno-zero-initialized-in-bss
Date: Mon, 20 Nov 2017 11:02:46 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0

On 11/20/2017 10:29 AM, Alexander Graf wrote:
> On 11/20/2017 10:27 AM, Christian Borntraeger wrote:
>> On 11/20/2017 10:19 AM, Alexander Graf wrote:
>>> On 11/20/2017 10:15 AM, Christian Borntraeger wrote:
>>>> The QEMU ELF loader does not initialize the bss segment. This has
>>>> triggered several bugs in the past, e.g. see commit 5d739a4787a5
>>>> ("s390-ccw.img: Fix sporadic errors with ccw boot image - initialize
>>>> css").
>>>> Instead of fixing these things one-by-one we can build the BIOS
>>>> with -fno-zero-initialized-in-bss. This will move the zero variables
>>>> also into the data segment, which is then part of a LOAD section.
>>> Doesn't this bloat the firmware? Why don't we just manually clear bss in 
>>> the firmware itself? It's what all other firmwares do :)
>> Yes the proper fix is to initialize bss in the bios itself.
>> I was trying to come up with something for 2.11, but since the patch does 
>> not solve the original issues, lets drop it.
> Initializing bss is quite simple. You can probably even do it from C. Just 
> set two variables before and after .bss in the linker script and memset(0) 
> from start to end :).

Yes, I know but then we have to change the build process to use a linker 
script.(we rely on the default
linker script right now).

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