How does IDA create COMMON, ABS and EXTERN segments of ELF-file?

Question

Some symbols (from symbol table) in ELF-file belong to special sections (COMMON, ABS, UNDEF).

IDA creates virtual sections for this symbols.

Subject: What is the rule (or set of rules) which IDA use to create these special sections (start address, size, alignment)?

Answer 1

According to IDA's ELF-loader and some tests.

The order of sections in REL-file:

1. COMMON
2. ABS
3. EXTERN

The order of sections in EXEC-file (there is no COMMON section):

1. EXTERN
2. ABS

The rules of section creation are:

1. Take the adress after last real section
2. Calculate the size of each virtual section = number_of_symbols * 4
3. Create all needed virtual sections according to the right order
4. Fill all virtual sections with the corresponding symbols from symtab
5. Set End-address for each virtual section according to the real number of bytes (based on number of symbols in the section)