[Bug 108821] New: dlopen example with libm.so is incorrect

[Bug 108821] New: dlopen example with libm.so is incorrect

[bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r]

https://bugzilla.kernel.org/show_bug.cgi?id=108821

            Bug ID: 108821
           Summary: dlopen example with libm.so is incorrect
           Product: Documentation
           Version: unspecified
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P1
         Component: man-pages
          Assignee: documentation_man-pages-ztI5WcYan/vQLgFONoPN62D2FQJk+8+b@public.gmane.org
          Reporter: fweimer-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org
        Regression: No

This does not work because libm.so can be a linker script:

           handle = dlopen("libm.so", RTLD_LAZY);

The proper way to do this is to include <gnu/lib-names.h> and use LIBM_SO.

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[Bug 108821] dlopen example with libm.so is incorrect

[bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r]

https://bugzilla.kernel.org/show_bug.cgi?id=108821

Florian Weimer <fweimer-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://sourceware.org/bugz
                   |                            |illa/show_bug.cgi?id=18915

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[Bug 108821] dlopen example with libm.so is incorrect

[bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r]

https://bugzilla.kernel.org/show_bug.cgi?id=108821

Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org

--- Comment #1 from Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> ---
Hi Florian,

I'm reluctant code a glibc dependency into what I would like to be a fairly
vanilla dlopen example. What if I used a function from libc itself (e.g.,
strlen()). Does the same issue exist?

Cheers,

Michael

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[Bug 108821] dlopen example with libm.so is incorrect

[bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r]

https://bugzilla.kernel.org/show_bug.cgi?id=108821

--- Comment #2 from Florian Weimer <fweimer-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> ---
(In reply to Michael Kerrisk from comment #1)
> Hi Florian,
> 
> I'm reluctant code a glibc dependency into what I would like to be a fairly
> vanilla dlopen example.

Fair point.  Although the example might confuse users because even where it
works, it typically needs development packages at run time (because the .so
link are only installed by them).

> What if I used a function from libc itself (e.g.,
> strlen()). Does the same issue exist?

libc.so is a linker script, too.  libm.so.6 and libc.so.6 are not, but they are
glibc-specific to (some moderately current Solaris versions use libm.so.2 and
libc.so.1, for example).

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[Bug 108821] dlopen example with libm.so is incorrect

[bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r]

https://bugzilla.kernel.org/show_bug.cgi?id=108821

--- Comment #3 from Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> ---
So, I'm inclined to close this as WONTFIX. I mean: this example will work for
most people on most systems, right? The alternative is to create a bigger
example where I build a little library that is then dlopen()-ed. But that seems
like a little too much work, and might actually be less easy to understand than
the current example.

Do you have a strong objection to WONTFIX, Florian?

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[Bug 108821] dlopen example with libm.so is incorrect

[bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r]

https://bugzilla.kernel.org/show_bug.cgi?id=108821

--- Comment #4 from Florian Weimer <fweimer-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> ---
(In reply to Michael Kerrisk from comment #3)

> So, I'm inclined to close this as WONTFIX. I mean: this example will work
> for most people on most systems, right?

With glibc, libm.so is increasingly a linker script on x86_64 due to this
change:

  <https://sourceware.org/glibc/wiki/libmvec>

This was introduced in glibc 2.22, so few distributions have this change yet.

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[Bug 108821] dlopen example with libm.so is incorrect

[bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r]

https://bugzilla.kernel.org/show_bug.cgi?id=108821

Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |CODE_FIX

--- Comment #5 from Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> ---
Thanks for all of the info Florian. So, in the end it seems best to make the
change you already suggested :-}. Done!

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