[PATCH] Change representation of dllexport/dllimport

[Nick Lewycky]

On 11 September 2013 11:25, Robinson, Paul <
Paul_Robinson at playstation.sony.com> wrote:

>  My linker guys say that visibility and dllimport/dllexport are
> orthogonal, therefore I conclude that dllimport/dllexport should not be
> modeled as visibility values.  It may be that some combinations of
> visibility and import/export don't make sense, but that doesn't mean you
> have to make it syntactically impossible to express them.  (That's what
> semantic checking is for.)****
>
> ** **
>
> My linker guys are also agitating to make –fvisibility=hidden the default
> for our platform, which caused me to double-take at the thought of
> dllexport'ing a hidden symbol but they say it is a reasonable thing to do.
> We already default to –fPIC so we'd get a bit of a win by defaulting to
> –fvisibility=hidden as well (references to hidden symbols don't have to go
> through the GOT).  I'm not saying we want it to be the default for
> everybody, but rather it should be target-specific.****
>
> ** **
>
> I think this was settled previously in the thread but I thought I'd chime
> in that we use dllimport/dllexport and we are an ELF/non-Windows target.
>

Could you explain what it means to use dllimport and dllexport on an ELF
target?

Nick

****
>
> ** **
>
> *From:* llvm-commits-bounces at cs.uiuc.edu [mailto:
> llvm-commits-bounces at cs.uiuc.edu] *On Behalf Of *Reid Kleckner
> *Sent:* Wednesday, September 11, 2013 9:24 AM
> *To:* Nico Rieck; Chandler Carruth
> *Cc:* reviews+D1110+public+872068f434b7231c at llvm-reviews.chandlerc.com;
> llvm-commits
>
> *Subject:* Re: [PATCH] Change representation of dllexport/dllimport****
>
>  ** **
>
> On Wed, Sep 11, 2013 at 11:38 AM, Nico Rieck <nico.rieck at gmail.com> wrote:
> ****
>
>  On 09.09.2013 18:36, Reid Kleckner wrote:****
>
> How's this patch doing?  It's come up on the mailing lists a few times, so
> I thought I'd ping. :)****
>
> ** **
>
> I guess it's mainly lacking more feedback about which variant to pursue.
> As reasoned before, I don't really like conflating the term "visibility"
> with dllimport (it would also require making -fvisibility=hidden the
> default). But opinions on this have been very scarce.****
>
>  ** **
>
> As for opinions, everyone I talked to locally felt that if the export
> controls can't be combined with visibility, then there's no reason to make
> the invalid combinations representable in IR.  Maybe they'll chime in.****
>
> ** **
>
> I don't see a need to make -fvisibility=hidden the default, either.  I
> don't want to use the same enum for default visibility and dllexport.  It
> seems to me that default visibility should be the platform default
> visibility when linking DSOs, and dllexport should force a symbol into
> .drectve and possibly into .dynsym for ELF, if that's representable in a .o
> file.****
>
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