libtool C++ link bug with -lm functions with Sun Workshop compiler

[Tim Mooney]

I think I have discovered a bug in libtool's link behavior with the
Sun Workshop C++ compiler when creating a C++ library that requires libm.
I observed it on x86_64-sun-solaris2.10, but it may also affect the
Workshop C++ compiler on Linux too.  I found it when trying to build
GNU aspell 0.60.5.

If you have a configure.ac that calls AC_LANG([C++]), any subsequent
AC_CHECK_FUNCS will result in a link that uses the C++ compiler.  Because
the C++ compiler initiates the link, it automatically adds some libraries
to the final call to ld.  Which libraries it adds depends on what flags
CC was passed (arguments like -library=stlport4 change what C++ libraries
are automatically added).  The C++ compiler appears to always add `-lm
-lc' after the C++ libraries, though.

That means that doing something like


AC_INIT(lttest, 0.60.5)
AC_CONFIG_SRCDIR(configure.ac)
AC_PROG_CXX
AC_LANG([C++])

AC_CHECK_FUNCS(sqrt)
AC_OUTPUT


will always detect sqrt(), because the C++ compiler added `-lm -lc'
behind the scenes.

When libtool is called to generate a C++ library on Solaris, it doesn't
add -lm, though.  It only adds -lc.  That will result in link failures
if functions like sqrt(), floor(), etc. from libm are used by the C++
library.

Is the correct fix to just add -lm to the postdeps for Solaris and Linux
when using the Workshop compiler, or is there some other method that
should be used?  I'm talking about changing all instances of

      _LT_AC_TAGVAR(postdeps,$1)='-library=Cstd -library=Crun'

to

      _LT_AC_TAGVAR(postdeps,$1)='-library=Cstd -library=Crun -lm'

Tim
--
Tim Mooney                              address@hidden
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