Which section does objdump disassemble by default

Question

I am currently building a bare metal executeable, which contains some special sections containing code. However, when I do objdump -d I only get the code for the .text and .init.text sections. The manpage for objdump only says that it "only disassembles those sections which are expected to contain instructions" when using the -d option. What sections are these, and how does objdump tell which sections to decode? I know I can also use the -D option to get a full decoding of all sections, but this is usually much more than I need.

Answer 1

objdump internally uses libbfd to get section information. objdump passes a callback to bfd_map_over_sections() which calls the callback on each section. When called, libbfd passes a asection * to the callback, which has a member type. If the type contains the flags SEC_CONTENTS | SEC_CODE it gets disassembled by objdump when the -d option is passed.

Getting into libbfd is quite harder, I expect that the type detection depends on architecture, but I hope I gave you at least the right pointer. (Probably when having more time I'll dig more into this and extend the answer)..

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Btw, if you need a script to filter out the sections of interest from objdump -D you might use sed, like this:

# ------------Place section names here ---------------vvv 
objdump -D object.o | sed -rn '/Disassembly of.*\.(comment|text)/{:a;p;n;/Disassembly of/!ba}'