it's either, depending on whether you pretend that a vec3 is a mat3x1 or a mat1x3. The correct transform matrices for each of those arbitrary conventions will be transposed compared to the other.is it rows or columns? i can never remember. been way too long since i took linear.
The 3 row vectors of a rotation (row) matrix already define the side, up, and forward vectors of the local frame w.r.t. the parental frame.
IIRC, D3DX uses the opposite convention than what mathematicians tend to use, for some strange reason.