Removing RTTI from binaries

[Iain Buclaw via D.gnu]

On 14 January 2015 at 04:00, Mike via D.gnu <d.gnu at puremagic.com> wrote:
> On Tuesday, 13 January 2015 at 14:36:15 UTC, Dicebot wrote:
>>
>>
>> I remember speaking about it with Martin and Daniel during DConf 2014 and
>> I think it was Daniel who mentioned that by default TypeInfo/ModuleInfo is
>> emitted in some weird packed way. When LDC announced using --gc-sections by
>> default it was mentioned they had to change ModuleInfo emitting to make it
>> actually work.
>>
>> Can it be the same issue?
>
>
> Thanks, Dicebot, for bringing this to my attention.  That would
> explain what I'm seeing.
>
> Is this something unique to GDC, or is it an artifact inherited
> from DMD?
>
> Mike

It's an artifact inherited from DMD.

ModuleInfo is of a dynamic size, depending on what is implemented in the module.

See: https://github.com/D-Programming-Language/druntime/blob/081591237ee7d666ffd81463dac1b7f38e7d9798/src/object_.d#L1589

However it's size is correctly recorded before being sent to be written.

The ModuleInfo symbols themselves aren't put into any particular
section, they  also can't go in rodata because of how the D runtime
start-up works, so they end up in the same section as __gshared data.

The same is also true with TypeInfo_Class (alias ClassInfo) where
interface vtables are written packed immediately after the data
structure ends.  Again, it's size is treated as dynamic and is
correctly recorded before being written, and again it cannot be in
rodata because the __monitor field is directly written to.

Iain.