[Xen-devel] RE: Questions about VIRT_BASE and ELF_PADDR_OFFSET in __xen_guest

["Puthiyaparambil, Aravindh" <aravindh.puthiyaparambil@xxxxxxxxxx>]

> There is no reason really why VIRT_BASE=0 should not work. If it
> crashes there is presumably some underlying bug which disallowing
> VIRT_BASE=0 does not fix.

You are right. The experiment I was trying with Mini-OS was flawed. I
had forgotten to fix up the minios_x86_64.lds file to reflect 0x0 (bang
head on table). Once I did that things worked fine. 

Do we care about the situation where there is a mismatch in ELF header
and __xen_guest section? When this happens the var "pa" is calculated
incorrectly causing "parray" to go out of bounds.

pa = (phdr->p_paddr + done) - dsi->elf_paddr_offset; 
va = xc_map_foreign_range(xch, dom, PAGE_SIZE, PROT_WRITE, 
                          parray[pa>>PAGE_SHIFT]);

[line 227-228 xc_load_elf.c loadelfimage()]

(In my flawed test, p_addr was 0xffffffff80000000 and elf_paddr_offset
was 0 due to obvious reasons)

I know this is rarely possible unless someone does something stupid like
I did :-) which is why I am wondering if we should test for this case. 

[ASIDE]
Due to this I think I should fix x86_xx.S in Mini-OS so that it picks up
&_text from minios_x86_xx.lds.

Cheers,
Aravindh

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