dwarf generated file is treating 3 letters variables differently

Question

I am using a python script which runs OBJDUMP to extract dwarf information from an elf file, this is part of the code:

    # Run objdump to extract DWARF information from the ELF file
    ps = subprocess.Popen(path + "\\objdump --dwarf=info " + elf_file_name, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
    dwarf = ps.communicate()[0]

    # Iterate through each line of the decoded DWARF output
    for line in dwarf.decode("ascii").split('\n'):
        if line.strip().startswith("<"):
            .....
            .....

the problem is when i iterate through each line of the decoded DWARF output, it will have different ways of extracting variable information, for instance if i have 3 letters variables it will get only the name of the variable but if i have more than 3 letters it will get more information, you can see the photos below, does anyone have any idea why i get this.

enter image description here

Thank you.

For me it is because i have a script which retrieve information for each variable, so when i used 3 letter variable it didn't work, then when i debugged it i found out this, so i added a new handling, and i was wondering is this the only case in which it will not work or there are other cases which i don't know about — ziz
– ziz, Commented Apr 29, 2024 at 9:25
Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. — Community
– Community Bot, Commented Apr 29, 2024 at 16:30
Why parse objdump output? There are perfectly capable Python native DWARF parsing libraries. pyelftools is popular, for example. It resolves strp out of the box. — Seva Alekseyev
– Seva Alekseyev, Commented Nov 25, 2024 at 20:22

Armali · Accepted Answer · 2024-04-26 12:01:02Z

0

if i have 3 letters variables it will get only the name of the variable but if i have more than 3 letters it will get more information, …, does anyone have any idea why i get this.

The OSDev Wiki says:

If most attributes have a fixed size, a few attributes need to have some special handling:

DW_FORM_string attributes are a small zero-terminated string (so of variable length)
DW_FORM_strp attributes represent the offset inside the .debug_str section of the desired string

Of course you can only get more information (the offset into the .debug_str section) if it is there.

answered Apr 26, 2024 at 12:01

Armali

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1 Comment

ziz Over a year ago

Thank you for your response. Okey so the only thing i need to do is have some kind of handling for when i have extra information and when i don't have extra info

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