[Bug tools/28873] Implement eu-readelf -D

["mark at klomp dot org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=28873

--- Comment #8 from Mark Wielaard <mark at klomp dot org> ---
(In reply to Aaron Merey from comment #7) 
> This raises an interesting question: how do you calculate the number of
> symbols in .dynsym without using section headers?
> 
> I figured there'd some kind of "DT_SYMTABNUM" value somewhere but
> unfortunately the answer doesn't appear to be so straightforward.

It has been proposed, but not (yet) adopted:
https://groups.google.com/g/generic-abi/c/9L03yrxXPBc
(sorry, a google groups link, there should be a normal archive, but I cannot
find it right now). If that was adopted and linkers would generate it, then
this question would indeed have a simple answer. Sadly, it isn't :{

> Judging from the binutils readelf source code you need to use information in
> the .hash and .gnu.hash sections to calculate the number of entries. 
> 
> To complicate things even more, a binary can contain either .hash or
> .gnu.hash or both and computing the number of .dynsym entries is different
> in each case. See binutils/readelf.c:get_num_dynamic_syms, you may need to
> implement some of this in your patch.

If there is a .hash section then it is fairly easy, the first word is the
number of symbols the hash/symbol table describes.

If it is a .gnu.hash section then sadly you have to parse and go through the
whole hashtable and count.

There is an implementation already in elfutils, but it is a bit hiden and
obscure if you don't know what you are looking for. Search for "Figure out the
size of the symbol table" in libdwfl/dwfl_module_getdwarf.c.

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