What does rt/sections_elf_shared.d do? (Porting dmd to musl)

[Yuxuan Shui]

I'm trying to get dmd and phobos working with musl. Right now I 
have a bootstrapped compiler built with musl, which seems to work 
fine. However user applications will segmentation fault before 
even reaches main.

I investigated a bit. Looks like musl is not happy with how 
druntime uses dlopen related functions. When a D library loads, 
it tries to call _d_dso_registry, which will try to get a handle 
of the library using dlopen. Meaning dlopen will be called on the 
library itself while it's still loading. This seems to break 
musl. Although this might also be a bug on musl side: it tries to 
call init functions even when RTLD_NOLOAD is passed to dlopen.

However, going through sections_elf_shared.d, it makes me feel 
it's doing some magic tricks with dl functions, but I don't know 
what for?

If my understand is correct, it's used to register TLS storage to 
GC. If that's the case, there must be simpler ways to do that.