from zephyr.c:90
static const struct stack_register_offset arc_callee_saved[] = {
{ ARC_R13, 0, 32 },
{ ARC_R14, 4, 32 },
{ ARC_R15, 8, 32 },
{ ARC_R16, 12, 32 },
{ ARC_R17, 16, 32 },
{ ARC_R18, 20, 32 },
{ ARC_R19, 24, 32 },
{ ARC_R20, 28, 32 },
{ ARC_R21, 32, 32 },
{ ARC_R22, 36, 32 },
{ ARC_R23, 40, 32 },
{ ARC_R24, 44, 32 },
{ ARC_R25, 48, 32 },
{ ARC_GP, 52, 32 },
{ ARC_FP, 56, 32 },
{ ARC_R30, 60, 32 }
};