Experimental Physics and
Industrial Control System

"Wang Xiaoqiang" <[email protected]> · Thu, 7 May 2009 16:56:07 +0200

Hi,

Probably this is not interesting to anybody, but I made a temporary fix.

First I am wrong by saying it cannot link on win32-x86 because MS link
can 
handle this kind of self-reference. Here is the discussion exactly about
this,
http://blogs.msdn.com/oldnewthing/archive/2006/07/26/679044.aspx

So the problem is only about GNU linker. Although it cannot handle
self-reference,
it supports auto-import feature. In short, it does not require
__declspec(dllimport)
to import symbols from DLLs.
http://sourceware.org/binutils/docs-2.18/ld/WIN32.html

To make both happy, in shareLib.h I avoid the definition epicsShareXXX
for cygwin
Line 129
#       if defined(_DLL) && !defined(__CYGWIN32__)/* this indicates that
we are being compiled to call DLLs */
And then in configure/os/CONFIG.cygwin-x86.cygwin-x86 add
--enable-auto-import linker flag 
Line 23
SHRLIB_LDFLAGS = -shared
-Wl,--enable-auto-import,--out-implib,$(LIB_PREFIX)$*$(LIB_SUFFIX)
LOADABLE_SHRLIB_LDFLAGS = -shared
-Wl,--enable-auto-import,--out-implib,$(LIB_PREFIX)$*$(LIB_SUFFIX)

This may also apply to win32-x86-mingw, but I did not try.

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Wang Xiaoqiang
Sent: Wednesday, May 06, 2009 2:12 PM
To: epics
Subject: Failed to create single DLLs on Windows

Hi,

On windows, with cygwin-x86 and win32-x86 host arch, I have compiled
EPICS base to create shared libraries.

Then I setup a simple application to create a DLL, and it complains
undefined reference (error output below).
I understand that this is because epicsShareExtern is defined as
__declspec(dllimport).
Linker is instructed to call these functions in some DLLs which is not
true, since I also compiled these functions in.
On the other hand, it builds successfully using the Makefile.support,
which separates the actual functions to a DLL, to satisfy the linker.
That looks a bit awkward. 

Because of my limited knowledge, I would ask gurus, are there other
solutions to such a pecular situation. Actually asyn/testManager example
has a similar problem, which wants to creat a single EXE.

Thanks in advance.

==== here starts the make output for cygwin-x86 === make -C O.cygwin-x86
-f ../Makefile TOP=../../.. T_A=cygwin-x86 install
make[1]: Entering directory `/w/test/epicsdum/dumApp/src/O.cygwin-x86'
g++ -o dum.dll -shared -Wl,--out-implib,dum.lib
-L/usr/local/epics/base/lib/cygwin-x86
dum_registerRecordDeviceDriver.o dumHello.o    -lrecIoc -lsoftDevIoc
-lmiscIoc -lrsrvIoc -ldbtoolsIoc -lasIoc -ldbIoc -lregistryIoc
-ldbStaticIoc -lca -lCom  -lpthread   -lreadline -lcurses -lm
dum_registerRecordDeviceDriver.o:dum_registerRecordDeviceDriver.cpp:(.te
xt+0x7): undefined reference to `__imp__pvar_func_helloRegister'
dum_registerRecordDeviceDriver.o:dum_registerRecordDeviceDriver.cpp:(.te
xt+0x37): undefined reference to `__imp__pvar_func_helloRegister'
dum_registerRecordDeviceDriver.o:dum_registerRecordDeviceDriver.cpp:(.te
xt+0x58): undefined reference to `__imp__pvar_int_helloVariable'
Creating library file: dum.lib
collect2: ld returned 1 exit status
make[1]: *** [dum.dll] Error 1
make[1]: Leaving directory `/w/test/epicsdum/dumApp/src/O.cygwin-x86'

--
Dr. Xiaoqiang Wang
Paul Scherrer Institut, WBGB/010
5232 Villigen PSI, Switzerland

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System