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

From: Alexander Graf
Subject: Re: [Qemu-devel] [PATCH] pc-bios/s390-ccw: build s390 bios with -fno-zero-initialized-in-bss
Date: Mon, 20 Nov 2017 10:29:08 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.6.0

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

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 :).


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