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Invalid opcode exception error for HVC instruction

Nicola Johnsen
Note: This was originally posted on 9th November 2012 at http://forums.arm.com

Hi I'm developing a UEFI boot loader that can run a hypervisor. I've developed some code that initializes CPUs and then transitions from monitor mode into non-secure hyp mode. I've set up HVBAR etc but when I then call the hvc #0 assembly instruction, the runtime (UEFI tianocore on ARM Fast model simulator) reports an Invalid Opcode exception. I wonder what could be the reason for this exception? I'm using a Cortex-A15 so the instruction should be valid. I've also set SCE.HCE to 1 so the hvc instruction should be available in non-secure monitor mode. Is there anything else I'm missing here? I've already asked for help from the UEFI people but didn't get any response so I'm trying a different audience.

Cheers.
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  • Arm Employee Badge
    Note: This was originally posted on 12th November 2012 at http://forums.arm.com

    Actually what you described is what I had expected.  If you look at section B9.3.4 of the architecture reference manual (  rev C.b  ) it gives the pseudo code for the HVC instruction.  First bit reads:

    if !HasVirtExt() || IsSecure() || !CurrentModeIsNotUser() then UNDEFINED;

    Mon mode is always classed as secure, so you were falling over the the IsSecure() test.
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  • Arm Employee Badge
    Note: This was originally posted on 12th November 2012 at http://forums.arm.com

    Actually what you described is what I had expected.  If you look at section B9.3.4 of the architecture reference manual (  rev C.b  ) it gives the pseudo code for the HVC instruction.  First bit reads:

    if !HasVirtExt() || IsSecure() || !CurrentModeIsNotUser() then UNDEFINED;

    Mon mode is always classed as secure, so you were falling over the the IsSecure() test.
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