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

[Anup Patel]

Try this out one last time. I am sure you will be able to replicate the
problem.

Run qemu like this:
qemu-system-arm -M realview-pb-a8 -serial stdio -kernel arm_test.elf -s -S

and run arm-none-gnueabi-gdb with no arguments and in gdb type these
commands:

(gdb) target remote :1234
Remote debugging using :1234
0x00100000 in ?? ()
(gdb) si
0x00100054 in ?? ()
(gdb) si
0x00100054 in ?? ()
(gdb) si
0x00000008 in ?? ()

(I expect it to jump to 0x00000004 after 0x00100054)

--Anup

On Tue, Apr 12, 2011 at 5:40 PM, Anup Patel
<address@hidden>wrote:

> I see 0x00000008 ().
>
> I am using qemu-0.14.0.tar.gz available for QEMU Downloads.
>
> --Anup
>
>
> On Tue, Apr 12, 2011 at 5:12 PM, Peter Maydell <address@hidden>wrote:
>
>> > Also, in the test case hits 0x8 after encountering UNDEF instruction
>> at 0x100058.
>>
>> So if you run qemu like this:
>> qemu-system-arm -M realview-pb-a8 -serial stdio -kernel arm_test.elf -s -S
>>
>> and run arm-none-gnueabi-gdb with no arguments and in gdb type these
>> commands:
>>
>> (gdb) target remote :1234
>> Remote debugging using :1234
>> 0x00100000 in ?? ()
>> (gdb) break *0x4
>> Breakpoint 1 at 0x4
>> (gdb) break *0x8
>> Breakpoint 2 at 0x8
>> (gdb) c
>> Continuing.
>>
>> ...what does gdb do?
>> (For me it says "Breakpoint 1, 0x00000004 in ?? ()" which is what I
>> expect.)
>>
>> --
>> You received this bug notification because you are a direct subscriber
>> of the bug.
>> 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.
>>
>> To unsubscribe from this bug, go to:
>> https://bugs.launchpad.net/qemu/+bug/757702/+subscribe
>>
>
>

-- 
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
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.