Re: (dynamic-link "libm") doesn't work on guile

[Alex Vong <alexvong1995@gmail.com>]

ludo@gnu.org (Ludovic Courtès) writes:

> Alex Vong <alexvong1995@gmail.com> skribis:
>
>> ludo@gnu.org (Ludovic Courtès) writes:
>
> [...]
>
>>> I think that’s because libm.so and libc.so are linker scripts, whereas
>>> libm-2.22.so and libc-2.22.so are the actual ELF files:
>>>
>>> $ cat ~/.guix-profile/lib/libm.so
>>> /* GNU ld script
>>> */
>>> OUTPUT_FORMAT(elf64-x86-64)
>>> GROUP (
>>> /gnu/store/qv7bk62c22ms9i11dhfl71hnivyc82k2-glibc-2.22/lib/libm.so.6
>>> AS_NEEDED (
>>> /gnu/store/qv7bk62c22ms9i11dhfl71hnivyc82k2-glibc-2.22/lib/libmvec.so.1
>>> ) )
>>> $ cat ~/.guix-profile/lib/libc.so
>>> /* GNU ld script
>>>    Use the shared library, but some functions are only in
>>>    the static library, so try that secondarily.  */
>>> OUTPUT_FORMAT(elf64-x86-64)
>>> GROUP (
>>> /gnu/store/qv7bk62c22ms9i11dhfl71hnivyc82k2-glibc-2.22/lib/libc.so.6
>>> /gnu/store/qv7bk62c22ms9i11dhfl71hnivyc82k2-glibc-2.22/lib/libc_nonshared.a
>>> AS_NEEDED (
>>> /gnu/store/qv7bk62c22ms9i11dhfl71hnivyc82k2-glibc-2.22/lib/ld-linux-x86-64.so.2
>>> ) )
>>>
>> I think you are right, libm.so is a binary file in Debian,
>
> That’s because Debian uses libc < 2.22 (libc 2.22 introduced libmvec,
> hence the linker script.)
>
I see, this is new to me.

>> Is there way to specify an ABI version (I suppose 6 is the ABI version
>> since we have libm.so.6) when dlopening a shared library to avoid this
>> glitch?
>
> Unfortunately no, that’s a long-standing libltdl bug:
>
>   https://lists.gnu.org/archive/html/guile-devel/2011-03/msg00021.html
>   https://lists.gnu.org/archive/html/bug-libtool/2011-03/msg00029.html
>
One of replies suggested making symlink pointing to the library you want
to use and it works for me on Debian stable!


(use-modules (system foreign))

(let* ((tmpd (pointer->string ((pointer->procedure '* 
                                                   (dynamic-func "mkdtemp" 
                                                                 (dynamic-link))
                                                   '(*))
                               (string->pointer "/tmp/XXXXXX"))))
       (libc-path (string-append tmpd "/libc.so")))
  (begin (symlink "/lib/x86_64-linux-gnu/libc.so.6" libc-path)
         (setenv "LTDL_LIBRARY_PATH" tmpd)
         (let ((libc (dynamic-link "libc")))
           (delete-file libc-path)
           (rmdir tmpd)
           libc)))


would return `$2 = #<dynamic-object "libc">`.

I use the more secure function `mkdtemp' to create temporary directory,
but is it inheritedly dangerous to dynamic-link a symlink in /tmp? Does
this count as a workaround? (It works once you know the absolute path of
the shared library.)

> You’d make a lot of people happy by fixing libltdl.  ;-)
>
> Thanks,
> Ludo’.

Cheers,
Alex