__svc_indirect keyword passes an operation
code to the SVC handler in
__svc_indirect is a function qualifier.
It affects the type of a function.
svc_num) return-type function-name(int
Is the immediate value used in the
It is an expression evaluating to an integer in the range:
0 to 224-1 (a 24-bit value) in an ARM instruction
0-255 (an 8-bit value) in a 16-bit Thumb instruction.
Is the value passed in
r12to the handler to determine the function to perform.
To use the indirect mechanism, your system handlers must make
use of the
r12 value to select the required operation.