[Qemu-devel] [Bug 757702] Re: Undefined instruction exception starts at offset 0x8 instead of 0x4

[Peter Maydell]

Sorry, I didn't notice the footnote in table A5-22; I see what you mean
now. It's still not permanently-UNDEF space though and you'd really be
better off using that instead. In any case, qemu does properly UNDEF the
instruction so this is a bit of a diversion.

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https://bugs.launchpad.net/bugs/757702

Title:
  Undefined instruction exception starts at offset 0x8 instead of 0x4

Status in QEMU:
  New

Bug description:
  ARMv7a has lot of undefined instruction from its instruction opcode
  space. This undefined instructions are very useful for replacing
  sensitive non-priviledged instructions of guest operating systems
  (virtualization). The undefined instruction exception executes at
  <exception_base> + 0x4, where <exception_base> can be 0x0 or
  0xfff00000. Currently, in qemu 0.14.0 undefined instruction fault at
  0x8 offset instead of 0x4. This was not a problem with qemu 0.13.0,
  seems like this is a new bug. As as example, if we try to execute
  value "0xec019800" in qemu 0.14.0 then it should cause undefined
  exception at <exception_base>+0x4 since "0xec019800" is an undefined
  instruction.