livepatch: arm[32,64],x86: NOP test-case

livepatch: arm[32,64],x86: NOP test-case

The test-case is quite simple - we NOP the 'xen_minor_version'.
The amount of NOPs depends on the architecture.

On x86 the function is 11 bytes long:

   55                      push   %rbp      <- NOP
   48 89 e5                mov    %rsp,%rbp <- NOP
   b8 04 00 00 00          mov    $0x4,%eax <- NOP
   5d                      pop    %rbp      <- NOP
   c3                      retq

We can NOP everything but the last instruction (so 10 bytes).

On ARM64 its 8 bytes:

  52800100    mov w0, #0x8         <- NOP
  d65f03c0    ret

We can NOP the first instruction.

While on ARM32 there are 24 bytes:

  e52db004        push    {fp}       <- NOP
  e28db000        add     fp, sp, #0 <- NOP
  e3a00008        mov     r0, #8     <- NOP
  e24bd000        sub     sp, fp, #0 <- NOP
  e49db004        pop     {fp}       <- NOP
  e12fff1e        bx      lr

And we can NOP instructions 1 through 5.

Granted this code may be different per compiler!

Hence if anybody does run this test-case - they should
verify that the assumptions made here are correct.

Acked-by: Julien Grall <julien.grall@arm.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>