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Currently struct trapframe as the saved PC as the last member
and the SPSR as the first member.
I want to move SPSR from the first to the last member.
This is we can use the
srsdb sp!, #PSR_SCV32_MODE
to save LR & SPRS onto the SVC32 stack and the
to pull them off the stack and return from the exception.
These are ARMv6 instructions and simplify exception handling.
(6 for pushing and 5 for popping a trapframe compared to 11 and 9
for the non SRS/RFE using instructions).
The disadvantage is that for pre-ARMv6 it makes pull the frame more
difficult since have SPSR last isn't easy to deal with. But pushing
the initial frame is easier.
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