[Bug d/88150] Use sections_elf_shared.d on Solaris

[ro at CeBiTec dot Uni-Bielefeld.DE]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88150

--- Comment #11 from ro at CeBiTec dot Uni-Bielefeld.DE <ro at CeBiTec dot Uni-Bielefeld.DE> ---
> --- Comment #10 from Iain Buclaw <ibuclaw at gdcproject dot org> ---
> I've got a (horrible?) hack for getting tls_modid from Solaris.

Cool, and not really horrible ;-)  It's already this way in Solaris 9 (I
happen to have access to those sources and just checked), so we can
assume this is stable.

> Looking at dlinfo(RTLD_DI_LINKMAP):
>
> https://github.com/illumos/illumos-gate/blob/4e0c5eff9af325c80994e9527b7cb8b3a1ffd1d4/usr/src/cmd/sgs/rtld/common/dlfcns.c#L1927-L1934

I missed that because I initially looked only at public headers for
tlsmodid, and Rt_map is private to ld.so.1.  This is intentionally
missing from dlinfo(3C), too.  I only found it in <rtld_db.h>'s
rd_loadobj_t, but it seemed hard to apply librtld_db to the current
process instead of one being debugged...

> Interestingly, Solaris sets the first tlsmodid to zero.
>
> https://github.com/illumos/illumos-gate/blob/8a06b3d6467c15646e663c05086378f16288af85/usr/src/cmd/sgs/rtld/common/tls.c#L52-L60
>
> This is in stark contrast to what elf_shared expects, given that there's an
> assert that it is always non-zero if _tlsSize is set.

Right: 0 had been used for the tlsmodid of the main executable until
dlpi_tls_modid was added to dl_phdr_info for Solaris 11.5 (still in
beta) when this would-be incompatibility with the Linux and BSD versions
was noticed.  It was only changed to 1 once it could be determined that
it was safe to do so.