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

[Prashant Vaibhav]

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