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Inline assembler BL and SVC output value list in C and C++ code

The BL and SVC instructions of the inline assembler have the following format:

SVC{cond} svc_num, {input_param_list}, {output_value_list}, {corrupt_reg_list}
BL{cond} function, {input_param_list}, {output_value_list}, {corrupt_reg_list}

output_value_list specifies the physical registers that contain the output values from the BL or SVC instruction and where they must be stored. The output values are specified as assignments from physical registers to modifiable lvalue expressions or as single physical register names.

The inline assembler takes the values from the specified physical registers and assigns them into the specified expressions. A physical register name specified without assignment causes the virtual register of the same name to be updated with the value from the physical register.

For example, the instruction:

BL foo, { }, { result1=r0, r1 }

generates the following pseudocode:

BL foo MOV result1, (physical) r0 MOV (virtual) r1, (physical) r1

By default, if you do not specify any output_value_list output values, register r0 is used for the output value.

Note

It is not possible to specify the lr, sp, or pc registers in the output value list.