[BUG] Floating point instructions clear capability

[Andreas-Bur]

Is there an existing CVA6 bug for this?

• I have searched the existing bug issues

Bug Description

Floating point instructions that write to an integer register unexpectedly clear the top half of the corresponding capability register. After a fcvt.w.d instruction for example, all fields of the corresponding capability are set to 0. This also happens with other instructions such as flt.d or feq.d.

PoC:

# Init FPU

  lui x11, 2
  csrrw x11, mstatus, x11
  addi x11, x0, 0
  csrrw x11, fcsr, x11

# Program

  fcvt.w.d x1,ft0
  cgettype x2,c1     # returns 0 instead of 0xffffffffffffffff
  cgetlen x3,c1      # returns 0 instead of 0xffffffffffffffff