X-Recipient: archive-cygwin AT delorie DOT com DomainKey-Signature: a=rsa-sha1; c=nofws; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:subject:to:references:from:cc:message-id:date :mime-version:in-reply-to:content-type :content-transfer-encoding; q=dns; s=default; b=gz2AR8IM9ZmPnNjv QX4fZkatL3O3oVGur19SPQaUHTYG4+puFi+ZwCFLQlb3CWWgWZDvjoG4DCcc2OrB U39P7s+sTMF331dMQCUgGyXRi8Eoj4b6wO4buHH80LqVbex6SUaTYVH0h/KXAPEi UXLCYkL0H154jG47ayBz23yFezo= DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:subject:to:references:from:cc:message-id:date :mime-version:in-reply-to:content-type :content-transfer-encoding; s=default; bh=sTK5TT49JZLq6P6hno3+gu jZbvU=; b=RpUxxs3Xm4neXukMpwxfM7pzG+4OzVUbxTquIsBuNTzlJ1hVph5RFr UCxMcPJJem+3ZAsY0mo+JHrxkpJkh54ikIUhW8/AwD+fCDnWibCLuMN+91x2dOOj horxzekfMuSxSn9d3j8APDRypwiF+RuX4U1Gr80NfvDn33ubSfIEQ= Mailing-List: contact cygwin-help AT cygwin DOT com; run by ezmlm List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: cygwin-owner AT cygwin DOT com Mail-Followup-To: cygwin AT cygwin DOT com Delivered-To: mailing list cygwin AT cygwin DOT com Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: =?ISO-8859-1?Q?No, score=-2.7 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_LOW autolearn=ham version=3.3.2 spammy=kaz, Kaz, it.=c2, DLLs.=c2?= X-HELO: out4-smtp.messagingengine.com X-ME-Sender: Subject: Re: Problem with differences with DLOPEN / DLSYM compared to ubuntu (16.04) / debian (stretch). To: The Cygwin Mailing List References: <94ac1558-0d01-2325-5a91-92e8b867a5bd AT gmail DOT com> From: Jon Turney Cc: Gary Schneir Message-ID: <374c9eed-e6bf-76c6-ffc3-cec5c97116a5@dronecode.org.uk> Date: Fri, 15 Sep 2017 17:59:14 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: <94ac1558-0d01-2325-5a91-92e8b867a5bd@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit On 15/09/2017 17:07, cyg Simple wrote: > Please consider using an interleaving method of posting on this list. > Top posting is considered rude. > > On 9/15/2017 9:51 AM, Gary Schneir wrote: >> Thanks for the response but I am a little confused by it.  If Cygwin is >> supposed to provide POSIX API functionality and DLOPEN / DLSYM are >> supported in CYGWIN, then I shouldn't care about the underlying >> complexity or restrictions of running within the Windows environment and >> using DLLs.  The behavior should be the same as in other POSIX environments. > > You presented your case well and I was waiting on someone familiar with > the code to respond. I'm not sure that would be Kaz, he was just trying > to be helpful from his experiences. I agree with your surmise that > Cygwin should perform similar results as Linux in this case. ... >> If you are saying that I did not include some sort of >> __declspec(dllexport) directive in my code so that it can find my >> symbols, that is something else but you indicate that you think cygwin >> hides that complexity in shared libraries. > > Actually it would be binutils, regardless of Cygwin or MinGW, that is > trying to hide the complexity of needing to supply the > __declspec([export|import]) declarations. The logic for that is a bit > confusing but if none is given then all symbols are exported. You need to decorate the symbols you wish to be visible with '__attribute__ ((dllexport))' or '__declspec(dllexport)' (MSVC syntax which is also supported by gcc) See [1] for an example of this done portably [1] https://gcc.gnu.org/wiki/Visibility Alternatively, you can use the ld flag --export-all-symbols (cf. with the ELF option --export-dynamic, which I think you must be using to get the observed behaviour on linux) to make all symbols visible. Taking your example, and making it compilable: $ cat dlopen.cc #include #include #include void * handle, * symbol; const char * errorStr; int main() { /* get access to the executable's symbol table */ handle = dlopen(NULL, RTLD_LAZY); errorStr = dlerror(); if (errorStr) { std::clog << "dlopen error '" << errorStr << "'" << std::endl; } if (handle) { std::clog << "handle ok " << std::endl; } else { std::clog << "handle NULL " << std::endl; } /* look up the from_string function */ symbol = dlsym(handle, "functionname"); errorStr = dlerror(); if (symbol) { std::clog << "dlsym symbol ok " << std::endl; } else { std::clog << "dlsym symbol NULL " << std::endl; } if (errorStr) { std::clog << "dlsym error '" << errorStr << "'" << std::endl; } } extern "C" __attribute__ ((dllexport)) void functionname() { } $ g++ dlopen.cc -o dlopen $ ./dlopen handle ok dlsym symbol ok -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple