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Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig
From: |
Daniel Thompson |
Subject: |
Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig |
Date: |
Tue, 22 Apr 2014 11:26:53 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.4.0 |
On 18/04/14 05:34, Nicolas Pitre wrote:
>> I'm not suggesting to break anything or changing existing platforms,
>> > but how do we improve the Image format in a compatible way. If
>> > bootloaders want to support booting Image files or vmlinux directly,
>> > then we should support that including any compatible changes to make
>> > things work better.
> And why would bootloaders want that? Just to create confusion with
> the established boot protocol?
I'd say that they don't. My original concern was how the different
architectures negotiate if more than one arch wants a special text
offset, not how to write a correct bootloader.
The existing uImage files already provide sufficient information to load
the kernel regardless of the TEXT_OFFSET chosen by negotiation among the
enabled architectures.
The entry point is PAGE_OFFSET + TEXT_OFFSET and, although only
implicitly defined, the entry point cannot be set to any other value
without making a backward incompatible to arm/Booting:
"The boot loader is expected to call the kernel image by jumping
directly to the first instruction of the kernel image."
Therefore providing PAGE_OFFSET remains 1G aligned and the hardware
meets the not-unreasonably-stupid test (i.e. TEXT_OFFSET < 1G) then
deriving the right value for TEXT_OFFSET is a trivial mask operation on
the entry point.
Daniel.
- Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig, (continued)
Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig, Rob Herring, 2014/04/17
- Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig, Nicolas Pitre, 2014/04/17
- Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig, Russell King - ARM Linux, 2014/04/17
- Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig, Rob Herring, 2014/04/17
- Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig, Russell King - ARM Linux, 2014/04/17
- Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig, Rob Herring, 2014/04/17
- Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig, Nicolas Pitre, 2014/04/18
- Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig,
Daniel Thompson <=
- Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig, Russell King - ARM Linux, 2014/04/22
- Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig, Daniel Thompson, 2014/04/22
Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig, Russell King - ARM Linux, 2014/04/18
Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig, Daniel Thompson, 2014/04/22
Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig, Russell King - ARM Linux, 2014/04/22