[lld] r207141 - [PECOFF] Define implicit symbols for exported ones.

[Rui Ueyama]

On Thu, Apr 24, 2014 at 1:29 PM, Chandler Carruth <chandlerc at google.com>wrote:

>
> On Thu, Apr 24, 2014 at 1:12 PM, Rui Ueyama <ruiu at google.com> wrote:
>
>> Using __imp_ symbols locally is I think not a good coding style. One
>> should just take an address using "&" operator rather than appending
>> __imp_ prefix. However, there are programs in the wild that depends
>> on this link.exe's behavior, so we need this feature.
>>
>
> I wonder if we should have a warning about this?
>

Ideally, yes, but there's no good way to print a warning message when some
symbol is actually linked. In this patch I create __imp_ symbols
unconditionally for all dllexported symbols. Creating them is not visible
to user -- using them should be warned.

I also wonder whether the cause in the wild is source code being shared
> between the DLL and the users of the DLL and being written "generically".
>

The program I spotted in the wild is ffmpeg. That has
/include:__imp_*sym* where
*sym* is a defined function in ffmpeg (/include is equivalent to
--undefined). Not sure why it has such option as it is basically no-op to
link.exe.

I don't think writing code generically cannot really justify to use __imp_
symbols, as you can just use "&", so I'm still wondering what this feature
is really for...
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