[Imtoolkit-users] libpng link problem on Linux (Ubuntu 18.04 LTS)

[Matthew K. <bur...@gm...>]

Hi,

On Linux, it looks like the build system is designed to use the system
libpng, but the resulting libim.so doesn't link against it:

/tmp/im-3.13_Linux415_64_lib$ ldd libim.so
        linux-vdso.so.1 (0x00007fff207bd000)
        libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007f58218b4000)
        libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6
(0x00007f582152b000)
        libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f582118d000)
        libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1
(0x00007f5820f75000)
        libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f5820b84000)
        /lib64/ld-linux-x86-64.so.2 (0x00007f5821e28000)

#include <stdio.h>
#include <dlfcn.h>
int main(int argc, char **argv) {
  void *result = dlopen(argv[1], RTLD_NOW);
  if (! result) {
    printf("error: %s\n", dlerror());
  }
  return 0;
}
// gcc -Wall -Werror testload.c -o testload -ldl

/tmp/im-3.13_Linux415_64_lib$ ~/Projects/testload $PWD/libim.so
error: /tmp/im-3.13_Linux415_64_lib/libim.so: undefined symbol:
png_get_sRGB

I also checked building from SVN and get the same result.

I think where the build system is doing LIBS += png, it should do something
like LIBS += png16 (at least on Ubuntu 18.04), but I'm not sure if that's
legit for all distros.

I can work around it by patching the libim.so shared object though:

/tmp/im-3.13_Linux415_64_lib$ patchelf --add-needed libpng16.so.16 libim.so
/tmp/im-3.13_Linux415_64_lib$ ~/Projects/testload $PWD/libim.so

/tmp/im-3.13_Linux415_64_lib$ ldd libim.so
        linux-vdso.so.1 (0x00007fffc4f4f000)
        libpng16.so.16 => /usr/lib/x86_64-linux-gnu/libpng16.so.16
(0x00007f0205a91000)
        libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007f0205874000)
        libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6
(0x00007f02054eb000)
        libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f020514d000)
        libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1
(0x00007f0204f35000)
        libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f0204b44000)
        /lib64/ld-linux-x86-64.so.2 (0x00007f0206022000)

At this point, I can load the shared object (and invoke PNG related things,
in Lisp, in my example):

CL-USER> (im-file:image-load
"/usr/share/backgrounds/Beaver_Wallpaper_Grey_4096x2304.png")
#<TECGRAF-BASE:IM-IMAGE {100249FBB3}>

The Windows builds do not have this problem.

Matt