Re: [Qemu-devel] Loading ELF binaries with very high base addresses

[Marc Lörner]

Hello Prashant,
first of all your "0x4<<64" is wrong it's "0x4<<60".
In Volume 2 of the IASDM page 2:46 you see that these three upper bits
correspond to the 8 virtual regions (here: region 2).
So maybe you can just disregard these bits and use the rest as new offset
to an faked guest_base that fits your needs (e.g. somewhere in your
process space)?

Regards,
Marc

>Hello,
>
>I am working on target-ia64, but am stuck during ia64 ELF loading.
>
>Referring to function "probe_guest_base()" in linux-user/elfload.c around 
>>line 1350, called from around line 1484 --
>
>When the main binary is being mmap'd, the host address and guest address 
>>should ideally be the same. If they're not, a linear search is done by 
>>increasing the host_address by one page and trying the mmap again. The 
>(positive) offset is then saved.

>The problem occurs with ia64 binaries, which typically start at 
>>0x4000000000000000  (i.e 0x4<<64). At least on my x86_64 host machine, 
>>mmap'ing at this address fails. The real_address is of the order of >0x8<<32. 
>Needless to say, increasing host_address and trying again will >never reach a 
>lower address to map at. Further, I cannot make it relocate >to a lower host 
>address because the offset (guest_base) is an unsigned >int and so the 
>relocation can only happen by a positive offset.
>
>Because of this it is not possible to load any ELF binaries which start >at 
>such high memory addresses. I can tailor an elf binary to start at a >lower 
>base address, which might work for that specific case, but I >suspect most 
>existing ia64 binaries start at 0x4<<64 by convention. Also, >the "hiaddr" is 
>read from elf header which again is set to 0x4<<64 + some >value.
>
>The existing code works fine with x86_64, for example, because the >binaries 
>are typically starting at 0x40000, which is easily mmap'd at >first try.
>
>Any ideas on a workaround?
>
>~Prashant
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