Segfault when adding a static destructor in druntime/src/rt/sections_elf_shared.d

[Steven Schveighoffer]

On 1/8/19 7:54 AM, RazvanN wrote:
> Hi all,
> 
> I am working on issue 14650 [1] and I would like to implement a solution 
> where static destructors are destroying global variables. However, I 
> have the following problem in druntime/src/rt/sections_elf_shared:
> 
> struct ThreadDSO
> {
>      DSO* _pdso;
>      static if (_pdso.sizeof == 8) uint _refCnt, _addCnt;
>      else static if (_pdso.sizeof == 4) ushort _refCnt, _addCnt;
>      else static assert(0, "unimplemented");
>      void[] _tlsRange;
>      alias _pdso this;
>      // update the _tlsRange for the executing thread
>      void updateTLSRange() nothrow @nogc
>      {
>          _tlsRange = _pdso.tlsRange();
>      }
> }
> Array!(ThreadDSO) _loadedDSOs;
> 
> 
> For this code, I would have to create the following static destructor:
> 
> static ~this() { _loadedDSOs.__dtor(); }
> 
> Because Array defines a destructor which sets its length to 0.
> 
> However this code leads to segfault when compiling any program with the 
> runtime (betterC code compiles successfully). In my attempt to debug it, 
> I dropped my patch and added the above mentioned static destructor 
> manually in druntime which lead to the same effect. Interestingly, 
> _loadedDSOs.__dtor runs successfully, the segmentation fault comes from 
> somewhere higher in the call path (outside of the _d_run_main function 
> (in rt/dmain2.d)). I'm thinking that the static destructor somehow 
> screws up the object which is later referenced after the main program 
> finished executing. Does someone well versed in druntime has any ideas 
> what's happening?

That is a thread-local static destructor. Are any shared static 
destructors accessing the array?

You might be able to determine this by printf debugging between calling 
unshared and shared destructors.

-Steve