<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>On Apr 24, 2014, at 1:57 PM, Rui Ueyama wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">On Thu, Apr 24, 2014 at 1:29 PM, Chandler Carruth <span dir="ltr"><<a href="mailto:chandlerc@google.com" target="_blank">chandlerc@google.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_extra"><div class=""><br><div class="gmail_quote">On Thu, Apr 24, 2014 at 1:12 PM, Rui Ueyama <span dir="ltr"><<a href="mailto:ruiu@google.com" target="_blank">ruiu@google.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="overflow:hidden">Using __imp_ symbols locally is I think not a good coding style. One<br>
should just take an address using "&" operator rather than appending<br>
__imp_ prefix. However, there are programs in the wild that depends<br>
on this link.exe's behavior, so we need this feature.</div></blockquote></div><br></div>I wonder if we should have a warning about this?</div></div></blockquote><div><br></div><div>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.</div></div></div></div></blockquote><div>It is possible to create the __imp_ atoms lazily. You have to add a linker internal File object which acts like a static archive. It only returns atoms when asked for an __imp_ symbol. The File object could then warn when an ImpPointerAtom is instantiated.</div><div><br></div><div>I'm not sure if the warning is worth the extra machinery this would require. Is there a (size) cost to always generating all the ImpPointerAtom atoms? The lazy way only instantiates ones that are used. </div><div><br></div><div>-Nick</div><div><br></div><br><blockquote type="cite"><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">
<div><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_extra">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".</div>
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</blockquote></div><br></div><div class="gmail_extra">The program I spotted in the wild is ffmpeg. That has /include:__imp_<i>sym</i> where <i>sym</i> 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.</div>
<div class="gmail_extra"><br></div><div class="gmail_extra">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...</div>
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