__attribute__((pcs("calling_convention"))) function attribute
This function attribute specifies the calling convention on targets with hardware floating-point, as an alternative to the __softfp keyword.
This function attribute is a GNU compiler extension that the ARM compiler supports.
__attribute__((pcs(" calling_convention ")))
Where calling_convention is one of the following:
uses integer registers, as for __softfp .
uses floating-point registers.