Can not get struct member addresses at compile time

[Doeme]

On Wednesday, 16 June 2021 at 23:20:26 UTC, Ali Çehreli wrote:
> Thank you, both. It still rules out an address at "compile 
> time" in general. For example, we cannot use such an address 
> when instantiating a template, or static array length, etc.
>
> And if I understand it correctly, there must be a pointer 
> *variable* for the linker to initialize. Fine then: That's how 
> this usage works for C but not for D. :)
>
> Thank you,
> Ali

Yes, there must be a pointer variable, which explains why we can 
not do compile time pointer arithmetic, which is fair and square 
(although I think it might be possible with some extra compiler 
effort). It does _not_ explain why we can't take addresses of 
struct members, though, since we have a pointer variable there!

Coming back to the working part of my first example:

```d
struct Foo{
	int bar;
}

__gshared Foo foo;
void *fooptr = &foo;
```

This works! And yields very similar relocations than the C 
version (plus some overhead and name-mangling):

```

[...]

0000000000000000  w    O 
.data._D19TypeInfo_S4test3Foo6__initZ	0000000000000091 
_D19TypeInfo_S4test3Foo6__initZ
0000000000000000 g     O .bss	0000000000000004 _D4test3Foo6__initZ
0000000000000004 g     O .bss	0000000000000004 _D4test3fooSQk3Foo
0000000000000000 g       .tdata.	0000000000000008 _D4test6fooptrPv
0000000000000000 g     O .rodata	000000000000000d 
_D4test12__ModuleInfoZ

[...]

RELOCATION RECORDS FOR [.tdata.]:
OFFSET           TYPE              VALUE
0000000000000000 R_X86_64_64       _D4test3fooSQk3Foo

[...]

```

The only difference is that the compiler will not pass down 
relocations plus an offset (i.e. relocating to a member of a 
struct) down to the linker, and I don't quite see a specific 
reason why it should not.