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}

corrupt_reg_list specifies the physical registers that are corrupted by the called function. If the condition flags are modified by the called function, you must specify the PSR in the corrupted register list.

The BL and SVC instructions always corrupt lr.

If corrupt_reg_list is omitted then for BL and SVC, the registers r0-r3, lr and the PSR are corrupted.

Only the branch instruction, B, can be used to jump to labels within a single C or C++ function.

By default, if you do not specify any corrupt_reg_list registers, r0 to r3, r14, and the PSR can be corrupted.