About the way of exception registration

About the way of exception registration

[Chao Li]

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Hi all,

I'm going porting LoongArch64 to UefiCpuPkg and OvmfPkg. A problem is 
blocked me that EFI_CPU_ARCH_PROTOCOL only provides interrupt register 
method, no exception register method.

I found that RISC-V hase the same issue, Andrei modified DebugSupport.h 
to fix it, commitid:69da506c927f8092ea8f783a092a694a3582e3ef. But this 
way may be not comply with UEFI SPEC, because in section 18 of UEFI 
SPEC, different architectures have been defined interupt types and 
exception types, and modifications like Andrei's will cause the UEFI 
SPEC and DebugSupport.h content to not match.

I also checked in AARCH64, they don't have this problem, because in 
AARCH64(ARM) uses synchronous exception, this exception is CPU internal 
exeption entry point, different type can separated by this entry point. 
So they just register this synchronous exception is fine,  and the 
exception filtering will be handled by the synchronous exception handler.

I think we need a way to reigster the exception, because some 
architectures like RISC-V and LoongArch don't have synchronous 
exception, and some one want to register exceptions to do some 
different. Can we add exception registration method at the end of 
EFI_CPU_ARCH_PROTOCOL? If not, I think there is only a modifcation like 
Andrei's, when the interrupt type and exception type use same numbers, 
put a flag in the highest bit to distinguish them. But I don't think 
this way is very suitable, just like above I talk about.

Hope to know your thoughts and look forward to hearing from you!



Thanks,
Chao

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