Re: [cmake-developers] target_link_libraries links mathlib as -lm rather than /libm.so, why?

[Brad King]

On 6/17/19 11:22 PM, Alan W. Irwin wrote:
> target_link_libraries(  /usr/lib/x86_64-linux-gnu/libm.so)
> 
> results in an actual link option "-lm".

Thanks.  I can reproduce that and have opened an issue with an explanation:

  https://gitlab.kitware.com/cmake/cmake/issues/19399

It occurs when the `.so` is a GNU ld script instead of an actual binary.

-Brad
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[cmake-developers] target_link_libraries links mathlib as -lm rather than /libm.so, why?

[Alan W. Irwin]

On Linux (Debian Testing) with CMake 3.13.2 (which I built myself)
I have a case where apparently

target_link_libraries(  /usr/lib/x86_64-linux-gnu/libm.so)

results in an actual link option "-lm".  Is this an exception to the
rule documented at

that if the full path is specified to target_link_libraries (as above)
that full path is used for the actual linking?

If so, I am curious about why this "CMake -lm exception" occurs and
are there other instances of such exceptions?  And shouldn't at least
the fact that there are still some exceptions be documented as part of
the CMP0060 documentation?

Note I discovered the above issue from a fairly short chain of
inference for the libLASi CMake-based build system, but if necessary,
I would be willing to attempt making a simple case demonstrating this
issue if it turns out that nobody here can verify it.

By the way, my use case is that some day I would likely to have the
option of building libLASi as static with *all* external libraries
static as well.  Of course, for that use case I could not use a
generic linking flag such as -lm which is why I am wondering
why "-lm" is being used for the actual link option above.

Alan
__
Alan W. Irwin

Programming affiliations with the FreeEOS equation-of-state
implementation for stellar interiors (freeeos.sf.net); the Time
Ephemerides project (timeephem.sf.net); PLplot scientific plotting
software package (plplot.org); the libLASi project
(unifont.org/lasi); the Loads of Linux Links project (loll.sf.net);
and the Linux Brochure Project (lbproject.sf.net).
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Linux-powered Science
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