FSSR: RISC-V instruction reference

fssrSwap FP control and status register Pseudo-instruction
Swaps the second register into the FP control and status register, storing its old value in the first, as an alias of fscsr.
RISC-V manual: csrrw 
Forms  fssr ,   
Same as fscsr t1, t2.
 fssr   
Same as fscsr t1.
Operands t1 Any integer register, x0 to x31, or its named alias, such as zero, t0 or t6. 
t2 An integer register. It may be the same register as t1. 
 # Initialize fcsr, then use fssr to read its old value or update it.
.text
li t3, 0
csrw t3, fcsr
li t0, 1
fssr t1, t0
# t1=0 is the old value; fcsr becomes 1.