Why does objdump not show .bss, .shstratab, .symtab and .strtab sections?

Question

I'm currently doing my own objdump implementation in C.

For my -s option, I have to show the full contents of the section of an ELF file.

I'm doing it well, but i'm showing more sections than the "real" objdump.

In fact, it does not output the .bss, .shstrtab, .symtab and .strtab sections.

I'm looking around the sh_flags value on the Shdr struct but I can't find any logic...

Why objdump -s does not shows these sections ?

Answer 1

Why objdump -s does not shows these sections ?

Objdump is based on libbfd, which abstracts away many complexities of ELF, and was written when objects tended to only have three sections.

As such, objdump is quite deficient. In addition to not showing you (some) existing sections, it may also "synthesize" sections that don't exist at all, and do other weird tricks. This is more of a libbfd fault -- its abstraction layer simply doesn't tell objdump about the "missing" sections.

TL;DR: don't use objdump. Use readelf instead.

Answer 2

Try using sh_size and sh_type, instead of sh_flags.

Quoting from the ELF specification

sh_size This member gives the section’s size in bytes. Unless the section type is SHT_NOBITS, the section occupies sh_size bytes in the file. A section of type SHT_NOBITS may have a non-zero size, but it occupies no space in the file