Gunzip failed at SSBL on stratix 10 soc dev kit board

Referring to, i got two questions.
At first , i found that only the Image and Image.gz can be build when compiling linux, that is weird. can uImage or zImage be built?
Secondly , In SSBL, the gunzip API is always successfully called, but decompressiong is always failed!!!
typically, error always accur beginning at the 20th byte. The source code i used is u-boot-socfpga_v2020.10. any one know why???