Re: lt_dlopen an uninstalled library

Hi Bob. I configured the GM build with '--with-modules', ran `make check` successfully. Then truncated the built .so files inside the 'coders/' dir to break it. Then reproduced the failure in gdb

    [il@reallin GM]$ export MAGICK_CONFIGURE_PATH='/home/il/builds/GM/config:/home/il/builds/GM/config'
    [il@reallin GM]$ export MAGICK_CODER_MODULE_PATH='/home/il/builds/GM/coders'
    [il@reallin GM]$ gdb --args ./tests/.libs/lt-constitute -storagetype char /home/il/builds/GM/tests/input_truecolor.miff bgr

So it turned out that the test program relies on the full path to the modules dir passed to the program and it calls lt_dlopen() with the full path. I guess I'll have to set the test environment in Makefile.am. Thanks.

┌─magick/module.c──────────────────────────────────────────────────────────────┐
│     1419      (void) LogMagickEvent(ConfigureEvent,GetMagickModule(),        │
│     1420        "Opening module at path \"%s\" ...", path);                  │
│     1421                                                                     │
│  >  1422      handle=lt_dlopen(path);                                        │
│     1423      if (handle == (ModuleHandle) NULL)                             │
│     1424        {                                                            │
│     1425          FormatString(message,"\"%.1024s: %.1024s\"",path,lt_dlerror│
│     1426          ThrowException(exception,ModuleError,UnableToLoadModule,mes│
│     1427          return(MagickFail);                                        │
│     1428        }                                                            │
│     1429      /*                                                             │
└──────────────────────────────────────────────────────────────────────────────┘
multi-thre Thread 0x7ffff73cc8 In: OpenModule          L1422 PC: 0x7ffff7e7bc6c 
(gdb) print path
$1 = "/.snapshots/persist/builds/GM/coders/miff.la\000\000\000\000\313|VUUU\000\
(gdb) 


On 23.11.2021 20:31, Bob Friesenhahn wrote:
> On Mon, 22 Nov 2021, ilya Basin wrote:
> 
>> Hi List.
>> I'm making a program with plugins as shared libraries and when I run `make check` I want my program to load the uninstalled plugins using lt_dlopen().
>>
>> I expected that passing `-dlopen libname.la` to libtool would force the generation of a wrapper script setting the proper LD_LIBRARY_PATH (just like regular linking with a shared .la does). However, an ELF binary is generated and and attempt to call lt_dlopen("libname.la") fails with "File not found". It only succeeds if the filename contains "./.libs/". What am I doing wrong?
> 
> I am not sure what the correct answer is.  Normally loadable modules do not have "lib" prefixes and so normally one does not use a "lib" prefix in conjunction with -module.  Use of "lib" prefixes is for shared libraries indended to be linked with using a linker (for software compilation).
> 
> When libtool builds shared libraries and modules, it puts them in a ".libs" subdirectory.  The ".la" file in the build directory should be enough for libltdl to load the module from the hidden ".libs" subdirectory.  When the module is installed, the a new ".la" file is created which is correct for the installed form, and the module may be re-linked while being installed.
> 
> Feel free to look at GraphicsMagick (http://www.GraphicsMagick.org/) source code for ideas.  GraphicsMagick uses lots of modules and its test suite works without installing the software.  It does not use libltdl's static-module "preloaded" feature.
> 
> Bob