Information about ARM System control registers.

As 42Bastian said, the different copies of the register apply to different ELs:

• SCTLR_EL3.A  controls strict alignment checking while executing in EL3
• SCTLR_EL2.A controls strict alignment checking while executing in EL2
• SCTLR_EL1.A controls strict alignment checking while executing in EL0 and LE1

The controls are independent so that different pieces of software can make different decisions. For example, a hypervisor (at EL2) might want A=1 and the OS might want A=0.  This way they each have the setting they want.

As 42Bastian said, the different copies of the register apply to different ELs:

• SCTLR_EL3.A  controls strict alignment checking while executing in EL3
• SCTLR_EL2.A controls strict alignment checking while executing in EL2
• SCTLR_EL1.A controls strict alignment checking while executing in EL0 and LE1

The controls are independent so that different pieces of software can make different decisions. For example, a hypervisor (at EL2) might want A=1 and the OS might want A=0.  This way they each have the setting they want.

1) Does this mean that, if i want to enable strict alignment checking in user process, all I have to do is set EL0 system control register?

2) Is there a way to change the bit during the runtime of the program (say a C program)? I am aware of ACLE system register(https://developer.arm.com/products/software-development-tools/compilers/arm-compiler-5/docs/101028/latest/9-system-register-access). But is this the function I use to change this?

EL0 has not dedicatated control register (read Martin's answer again).

EL0 cannot change settings of EL1 registers (or any others)-

Oh, i never noticed. Thanks for the information.

But is there a way to query the A bit of EL0 and EL1 registers respectively, if not change it?

Please read the ARMv8-A manual you were linking in another thread, for example:
UMA

A higher EL can read a lower EL's registers but not the other way round.  For example, EL2 can see (and modify) the EL1 setting if it wants to but EL1 can neither see nor modify the EL2 setting.

(EL2 needs to be able see and modify the EL1 to implement context switching of VMs.  An OS shouldn't care what setting the hypervisor is using, because it has not direct impact on the OS)