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Re: "ELF-Symbols" tag for relocatable images

From: Daniel Kiper
Subject: Re: "ELF-Symbols" tag for relocatable images
Date: Wed, 22 Mar 2017 20:23:50 +0100
User-agent: Mutt/1.3.28i

On Wed, Mar 22, 2017 at 04:43:35PM +0100, Rodrigo Vali??a Guti??rrez wrote:
> >> They also may not match if virtual address != physical address, but as
> >> we do not establish any address translation when launching image, this
> >> probably is going to fail. Still would be good to have this assumption
> >> explicitly listed in multiboot2 manual.
> >
> > I think that we should state in multiboot2 spec that physical address ==
> > virtual address in ELF.
> That may be true (that is going to fail) for entry point address, but
> please note that many kernels have the entry point and bootstrap code
> in a section/segment with virtual == physical, but then setup address
> translation and jump to another sections/segments with virtual !=
> physical addresses.

OK, even if we assume that virtual and physical addresses can be different
in the ELF header I think that the bootloader should always put into sh_addr
(maybe others) physical addresses. Usually it (the bootloader) does not have
sufficient knowledge to properly calculate correct kernel virtual addresses.
However, kernel is sufficiently smart to translate physical addresses to
virtual ones.


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