ARM AArch32 ABI Convention
==========================

https://github.com/ARM-software/abi-aa/blob/main/aapcs32/aapcs32.rst


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Registers R0-3 are also, by convention, used to hold parameter values to be passed to a subroutine or function. Functions with more than four parameters typically use one or more of those parameter registers to hold addresses pointing to data structures in memory.