Do not use "movs rd, rs" nor "movs rd, #imm" in Thumb2 mode.
Two reasons: - The movs is not supported if rd or rs is r13 (the stack ptr register). Newer versions of GNU as reject it, older versions were probably emulating it. - The purpose of setting the "s" flag on some operations is to enable 16-bit encoding in Thumb2 mode. However, for "mov" it is the non-s form that has a 16-bit encoding; the s form is never more compact.