HVC
Hypervisor Call causes a Hypervisor Call exception. For more information see Hypervisor Call (HVC) exception. Non-secure software executing at EL1 can use this instruction to call the hypervisor to request a service.
The HVC instruction is:
- undefined in Secure state, and in User mode in Non-secure state.
- When SCR.HCE is set to 0, undefined in Non-secure EL1 modes and constrained unpredictable in Hyp mode.
On executing an HVC instruction, the HSR, Hyp Syndrome Register reports the exception as a Hypervisor Call exception, using the EC value 0x12, and captures the value of the immediate argument, see Use of the HSR.
It has encodings from the following instruction sets: A32 ( A1 ) and T32 ( T1 ) .
A1
31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
!= 1111 | 0 | 0 | 0 | 1 | 0 | 1 | 0 | 0 | imm12 | 0 | 1 | 1 | 1 | imm4 | |||||||||||||||||
cond |
if cond != '1110' then UNPREDICTABLE; imm16 = imm12:imm4;
CONSTRAINED UNPREDICTABLE behavior
If cond != '1110', then one of the following behaviors must occur:
- The instruction is undefined.
- The instruction executes as NOP.
- The instruction executes unconditionally.
- The instruction executes conditionally.
T1
15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
1 | 1 | 1 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | imm4 | 1 | 0 | 0 | 0 | imm12 |
imm16 = imm4:imm12; if InITBlock() then UNPREDICTABLE;
For more information about the constrained unpredictable behavior of this instruction, see Architectural Constraints on UNPREDICTABLE behaviors.
Assembler Symbols
<q> |
See Standard assembler syntax fields. An HVC instruction must be unconditional. |
Operation
EncodingSpecificOperations(); if !HaveEL(EL2) || PSTATE.EL == EL0 || (IsSecure() && !IsSecureEL2Enabled()) then UNDEFINED; if HaveEL(EL3) then if ELUsingAArch32(EL3) && SCR.HCE == '0' && PSTATE.EL == EL2 then UNPREDICTABLE; else hvc_enable = SCR_GEN[].HCE; else hvc_enable = if ELUsingAArch32(EL2) then NOT(HCR.HCD) else NOT(HCR_EL2.HCD); if hvc_enable == '0' then UNDEFINED; else AArch32.CallHypervisor(imm16);
CONSTRAINED UNPREDICTABLE behavior
If ELUsingAArch32(EL3) && SCR.HCE == '0' && PSTATE.EL == EL2, then one of the following behaviors must occur:
- The instruction is undefined.
- The instruction executes as NOP.