ELF questions.

I’ve been playing with the GNU Bintools for QNX, but I have some difficulties.

From the QNX website I understand that with objdump the content of an ELF file can be explored and even can be extracted.
I’ve tried objdump -Dxsf but no result with regards to extracting the content.

editelf can update the ELF header. Under which circumstances is this used? I’d expect that editelf was also capable of updating other parts of the ELF, like included binaries. It there a way to update ELF files without recompiling?

ELF checksums and signatures
I’ve searched for information regarding ELF checksums and signatures, but I can’t find any usable information. There is information available about ELF file formats, but I found nothing about checksums and signatures