You can use nm and size to get the size of functions and ELF sections.
To get the size of the functions (and objects with static storage duration):
$ nm --print-size --size-sort --radix=d tst.o
The second column shows the size in decimal of function and objects.
To get the size of the sections:
$ size -A -d tst.o
The second column shows the size in decimal of the sections.