Issue 13938 & 13939 - Disallow non-trivial variable accesses in iasm

[9rnsr]

Issue 13938 - IASM shouldn't be able to access TLS variables
Issue 13939 - IASM shouldn't access global symbol with PIC code

[yebblies]

Ok, but then how do you load the tls/got offset of the variable?

[9rnsr]

Isn't it platform dependent? A portable way is, first load the TLS in a local var, then access the local from iasm.

void main()
{
    static int val;
    int tmp = val;   // portable load
    asm { mov EAX, tmp;}
}

[9rnsr]

@MartinNowak In OSX platform, -fPIC is enabled by default. So all __gshared variables cannot be accessible from iasm code. Is it correct behavior?

[yebblies]

I dunno, loading the variable outside the asm won't work in naked functions. Can we disable the obvious way, but still allow some way to do it?

https://issues.dlang.org/show_bug.cgi?id=7720

[MartinNowak]

Ok, but then how do you load the tls/got offset of the variable?

Oh, I tried at some point, it wasn't possible because you need a special relocation for that (on i386 which doesn't support RIP relative addressing).

That might be a way to get it.
https://issues.dlang.org/show_bug.cgi?id=12085

[MartinNowak]

@MartinNowak In OSX platform, -fPIC is enabled by default. So all __gshared variables cannot be accessible from iasm code. Is it correct behavior?

That might a bit too harsh, I commented on the tickets.

[MartinNowak]

Ultimatively I think it's the right choice to disable them (see Issue 9378 unless we add a more features to the IASM (like emitting relocations).