Consider the following snippet:

    struct Biggy {
        ulong[50000] a;
    }
    __gshared Biggy biggy;

    void main() {
        biggy = Biggy.init;
    }

produces the following code

    Dump of assembler code for function _Dmain:
    ...
    => 0x000000000047fa04 <+4>:	movabs $0x6faef0,%rsi
       0x000000000047fa0e <+14>:	movabs $0x7d6a90,%rdi
       0x000000000047fa18 <+24>:	mov    $0x1b774,%ecx
       0x000000000047fa1d <+29>:	rep movsq %ds:(%rsi),%es:(%rdi)

which is fine. However, adding a @disable this(this) to Biggy, i.e.,

    struct Biggy {
        ulong[50000] a;
        @disable this(this);
    }

produces

    Dump of assembler code for function _Dmain:
    ...
    => 0x000000000047fba4 <+4>:	movabs $0x7d6a88,%rsi
       0x000000000047fbae <+14>:	mov    $0x1b774,%ecx
       0x000000000047fbb3 <+19>:	pushq  (%rsi)
       0x000000000047fbb5 <+21>:	sub    $0x8,%rsi
       0x000000000047fbb9 <+25>:	loop   0x47fbb3 <_Dmain+19>
       0x000000000047fbbb <+27>:	movabs $0x7d6a90,%rdi
       0x000000000047fbc5 <+37>:	callq  0x47fb70 <_D7themain5Biggy8opAssignMFNaNbNcNiNjNfS7themain5BiggyZS7themain5Biggy>
       0x000000000047fbca <+42>:	add    $0xdbba0,%rsp

which, as you can see, copies Biggy.init onto the *stack* and then calls opAssign on it. Notice that Biggy does not define opAssign, and even if it did,  it doesn't make sense to *copy* the type's init to a temp location. 

Now since Biggy is big (~400KB), and the function is run on a stack-constrained fiber, we got a very peculiar segfault. 

Is there any reason for this odd behavior? I would have used memcpy, but &Biggy.init won't compile. 


-tomer (weka.io)