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Reply-To: moss AT cs DOT umass DOT edu
Subject: Re: Help debugging a dll issue
References: <b21c0ab1-341b-d6f5-915b-f73973b8079b AT cs DOT umass DOT edu> <830e7bcd-aeb5-264e-6436-799dfa54d7a0 AT cs DOT umass DOT edu> <nhr30c$qm5$1 AT ger DOT gmane DOT org>
To: cygwin AT cygwin DOT com
From: Eliot Moss <moss AT cs DOT umass DOT edu>
Message-ID: <d704ffd1-f76c-1a75-e487-d6f15bbe6ece@cs.umass.edu>
Date: Sat, 21 May 2016 22:52:42 -0400
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On 5/21/2016 9:45 PM, René Berber wrote:
> On 5/21/2016 6:30 PM, Eliot Moss wrote:
>
> [snip]
>> I used binary search, eliminating .o files from the .dll on the thought
>> that it was either a particular .o file that was leading to a problem,
>> or possibly the overall size (this is a huge link!).  I found that a .dll
>> with 58725 section 1 symbols (as reported by objdump -t) works, and one
>> with 66675 section one symbols fails.  So it appears to be a size issue.
>
> That's telling, since USHRT_MAX (65535) may be the limit, then somewhere
> there is the use of a variable of that type (unsigned short int,
> uint16_t), which may be part of some specification (i.e. the format of
> libraries).
>
> Supporting that is: https://ghc.haskell.org/trac/ghc/ticket/5292 which
> mentions:
>
> "65536 symbols. This is the limit that Windows DLLs can handle (the
> source of the limitation is that they use 16-bit integers to represent
> "ordinals")"
>
> and also point to an interesting bug report (5 years old):
>
> https://sourceware.org/bugzilla/show_bug.cgi?id=12969
>
> No answers, but at least an explanation.

Why the maintainers did not fix this, I don't know -- would have saved
me a week of effort tacking things down!

The solution was to use __declspec(dllexport), sparingly, so that only
a few symbols would be exported, and to drop --export-all-symbols. (How
did that work before?  Was the system a lot smaller?)  Supposedly
__attribute__((dllexport)) also works, though I did not try it -- using
__declspec was more in line with code for Windows native C compilers.

At least this thread may help someone in the future!

Regards -- Eliot

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