_REG_R4
u->uc_mcontext.__gregs[_REG_R4] = (__greg_t) arg;
gr[_REG_R4 - i] = va_arg(ap, int); /* sic! see mcontext.h */
gr[_REG_R4] = tf->tf_reg[4];
tf->tf_reg[4] = gr[_REG_R4];
gr[_REG_R4] = tf->tf_r4;
tf->tf_r4 = gr[_REG_R4];
gr[_REG_R4] = tf->tf_r4;
tf->tf_r4 = gr[_REG_R4];
gr[_REG_R4] = tf->tf_r4;
tf->tf_r4 = gr[_REG_R4];
gr[_REG_R4] = luc->luc_mcontext.arm_r4;
luc->luc_mcontext.arm_r4 = gr[_REG_R4];