Should strip discard the .ctf section ?

[Nick Alcock]

On 8 Oct 2019, Nick Alcock verbalised:

> (Hah! Thank you for spotting a horrible mistake on my part: see below.
> Fix forthcoming.)

Oh wait no, I am hallucinating and forgetting my own code.

> On 8 Oct 2019, Fangrui Song said:
>> --strip-all removes .symtab and .strtab. If .ctf references .symtab but
>> is not stripped along with .symtab and .strtab, the resulting .ctf will
>> just be broken.
>
> ... good point! This is clearly a horrible mistake on my part. Phew,
> thank goodness you spotted this one early.
>
> The gain here is mostly from sharing symbol name strings, so I think we
> should be sharing with .dynstr, since that's where the symtab strings
> are kept and frankly it's the only symtab with significant amounts of
> useful content in a stripped executable. Illumos uses the concatenation
> of .dynstr and .SUNW_ldynsym, the latter being an executable-only string
> table used to allow symtab lookups to work on stripped executables. We
> don't have .ldynsym (not yet, anyway) so sharing with .dynstr alone is
> clearly right.
>
> (It would be nice if we could share with both that *and* .strtab, but
> since .strtab is hardly ever there I don't think this is likely to be
> worth doing. We could share with .strtab in statically-linked
> executables only but I don't think they're common enough to be worth
> special-casing.)

It turns out that I thought of this already, and even wrote a comment
about it, and forgot that I'd done so. We specifically use the
symstrtab, i.e. whatever string table the symbol names are in, and use
the symtab's sh_link to find it at ctf_open time: so, on ELF, we end up
doing the right thing automatically. See the call to examine_strtab() in
elf_link_swap_symbols_out(), and the use of sh_link in
libctf/ctf-open-bfd.c:ctf_bfdopen_ctfsect().

Phew! Sorry for the mislead. We are fine here I think.

I will make a special note in the spec, since it is clear that this is
something that is easily got wrong! (In partial mitigation, I haven't
slept for two days...)