Why does call modify x6 ?

[Bobb56]

The pseudo instruction call modifies x6 as it's defined in pseudoops.txt
But it is not supposed to do it.
Call must be replaced by :
auipc x1,PCH1 ;jalr x1, x1, PCL1
And not :
auipc x6,PCH1 ;jalr x1, x6, PCL1

The pseudo op tail has to modify x6 because it should preserve the value of ra, but not call.