Can't Detect MIPS64 ELFs By Default

[fuzyll]

Bug Description:
We appear to be unable to accurately detect that an ELF is mips64 instead of mips32 by default. I suspect this is because the e_machine does not make a distinction between the two, and we rely on that to determine the default architecture.

You can work around this by using Open with Options and changing architecture and platform to mips64. But, it's easy to miss, and even easier if you don't have apriori knowledge of which architecture is correct.

Steps To Reproduce:

1. Open any MIPS64 binary.
2. Observe that it defaults to mips32.

Expected Behavior:
We open things as mips64 when they are.

[lwerdna]

repro:

busybox-mips64.zip

then in the python window:

>>> bv.arch
<arch: mips32>

(should be mips64)

The Elf64_hdr .e_machine field is just EM_MIPS (so nothing to distinguish the 32/64 on), but we should look also to the .e_ident[EI_CLASS] field which has value 0x2 (marking 64-bit).

[lwerdna]

I was expecting to add some code that would look to .e_ident[EI_CLASS]. Instead, we're going to mix that field into the identifier when we register the architecture.

Currently, we use .e_machine as an architecture ID when we call RegisterArchitecture(). Now for those architectures whose ID here is not selective enough (like for MIPS, 8 is used by both 32-bit and 64-bit elfs), their ID will be augmented with .e_ident[EI_CLASS] shifted to bit position 16.

So instead of calling RegisterArchitecture() with EM_MIPS (8) all alone, we call it with 0x10008 for 32-bit and 0x20008 for 64-bit.

Commit in arch-mips: Vector35/arch-mips@c8e2d4a
Commit in view-elf: Vector35/view-elf@b651c02
Commit in binja: https://github.com/Vector35/binaryninja/commit/138c8688527f71fe0120a0751cb9c08053a00a35