Re: CHECK_STATIC_TLS in R_X86_64_TPOFF64 type relocation

[Fengkai Sun <qcloud1014@gmail.com>]

Hi Florian,

Thanks for your reply!

I figure out that dlopened DSOs could use the initial-exec model: as long
as they can have access to static TLS, they are the same as DSOs introduced
by the main executable.

However, I am confused why (and when) the link editor emits initial-exec
for DSOs, because this model is not guaranteed to work. If the TLS segment
in a dlopened DSO is too large to fit in static space, it will fail the
main program and the user does not have a way to fix it. In contrast, the
two dynamic models always work.

Sorry if this sounds deviated and like a linker-related question.


---
Thanks,
Fengkai

On Sun, Dec 26, 2021 at 11:48 PM Florian Weimer <fw@deneb.enyo.de> wrote:

> * Fengkai Sun via Libc-help:
>
> >> We are trying to perform a static TLS relocation in MAP, but it was
> > dynamically loaded.
> >
> > To the best of my knowledge, I found that R_X86_64_TPOFF64 is for
> > Initial-exec TLS model, which only appears in executables.
>
> No, initial-exec in shared objects is fine (as long as static TLS
> space is available).
>
> Local-exec TLS in executables does not need relocations, and the link
> editor typically relaxes initial-exec TLS reference in main programs
> to local-exec TLS, leaving no of them trace (except for the PT_TLS
> segment).
>