Hi all,I noticed there are multiple system control registers in ARM.
The SCTLR_EL1 , SCTLR_EL2 and SCTLR_EL3.
I want to know, what do multiple such system controls registers represent??
I am particularly interested in the A bit of the system control register.
How does the A bit work when all these registers are involved?
For instance, When the A bit is enabled in say SCTLR_EL1 but not in SCTLR_EL2, what happen in case of an unaligned access?
Do we encounter a segmentation fault?
if yes why?
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
User Mask Access. Controls access to interrupt masks from EL0, when EL0 is using AArch64.
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)