gcc/libstdc++-v3/docs/configopts.html
Phil Edwards 8bd636c511 acinclude.m4: Clean up comments on newer checks.
2000-05-19  Phil Edwards  <pme@sourceware.cygnus.com>

	* acinclude.m4:  Clean up comments on newer checks.
	  (GLIBCPP_CHECK_COMPILER_VERSION):  Check for system_header
	  pragma support.  Remove WERRORSUPPRESS variable, add WERROR.
	* aclocal.m4:  Regenerate.
	* configure:  Regenerate.
	* Makefile.in:  Regenerate.
	* libio/Makefile.in:  Regenerate.
	* math/Makefile.in:  Regenerate.
	* src/Makefile.am:  Tell make's WERROR to depend on configure's WERROR.
	* src/Makefile.in:  Regenerate.
	* docs/configopts.html:  Document changes to --enable names.

From-SVN: r34034
2000-05-19 19:55:50 +00:00

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<H1 CLASS="centered"><A NAME="top">Interesting <TT>configure</TT>
options</A></H1>
<P>The latest version of this document is always available at
<A HREF="http://sourceware.cygnus.com/libstdc++/configopts.html">
http://sourceware.cygnus.com/libstdc++/configopts.html</A>.
</P>
<P>To the <A HREF="index.html">libstdc++-v3 homepage</A>.
<!-- ####################################################### -->
<HR>
<P>Here are some of the non-obvious options to libstdc++'s configure.
Keep in mind that
<!-- This SECnn should be the "Choosing Package Options" section. -->
<A HREF="http://sourceware.cygnus.com/autoconf/autoconf.html#SEC74">they
all have opposite forms as well</A>
(enable/disable and with/without). The defaults are for the latest
snapshot, 2.90.8.
<DL>
<DT><TT>--enable-multilib </TT>[default]
<DD><P>This is part of the generic multilib support for building
cross compilers. As such, targets like "powerpc-elf" will be
have libstdc++ built many different ways: "-msoft-float" and
not, etc. A different libstdc++ will be built for each of the
different multilib versions. This option is on by default.
</P>
<DT><TT>--enable-debug </TT>
<DD><P>The configure script will automatically detect the highest level
of optimization that the compiler in use can use (certain
versions of g++ will ICE if given the <TT>-O2</TT> option, but
this is fixed in later versions of the compiler). This --enable
flag will disable all optimizations and instruct the compiler to
emit as much extra debugging information as it can, for use
inside GDB.
</P>
<DT><TT>--enable-cstdio </TT>[default]
<DD><P>This is an abbreviated form of <TT>'--enable-cstdio=libio'</TT>
(described next).
</P>
<DT><TT>--enable-cstdio=LIB </TT>
<DD><P>Select a target-specific I/O package. As of libstdc++-v3
snapshot 2.90.8, the choices are 'libio' to specify the GNU
I/O package (from
<A HREF="http://sourceware.cygnus.com/glibc/">glibc</A>, the
GNU C library), or 'wince' to specify the Microsoft Windows CE
library. Eventually a generic cstdio interface will be added
so that people who want to use libstdc++-v3 with say, the Palm
Pilot, will be able to use libstdc++-v3 without libio.
</P>
<DT><TT>--enable-long-long </TT>
<DD><P>The &quot;long long&quot; type was introduced in C99. It is
provided as a GNU extension to C++98 in g++. This flag builds
support for &quot;long long&quot; into the library (specialized
templates and the like).
</P>
<DT><TT>--enable-namespaces </TT>[default]
<DD><P>By default, g++ currently ignores namespace <TT>std</TT> for
backwards compatibility. It can be turned on with the
<TT> -fhonor-std </TT> flag to the compiler. As of libstdc++-v3
snapshot 2.90.8, that flag is passed to g++ when building the
library. (In g++ 2.96 and later, this flag is on by default if
libstdc++-v3 is used.) The --disable variant will put all std::
symbols into the global namespace.
</P>
<DT><TT>--enable-cshadow-headers </TT>
<DD><P>This turns on the code to construct shadowed C headers. Very
experimental as of this writing.
</P>
<DT><TT>--enable-threads </TT>
<DD><P>This is an abbreviated form of <TT>'--enable-threads=yes'</TT>
(described next).
</P>
<DT><TT>--enable-threads=LIB </TT>
<DD><P>Select a threading library. As of libstdc++-v3 snapshot 2.90.8,
the choices are:
'yes' for some kind of default (hmmmmm);
'decosf1', 'irix', 'mach', 'os2', 'posix'/'pthreads'
(same thing),
'solaris', 'win32', 'dce', or 'vxworks' to select the
corresponding interface;
and 'single', 'no', or 'none' for the null-case,
single-threaded library.
</P>
<P>All of this is currently undergoing a lot of changes. As of
2.90.8, 'single' and 'posix' are the only implemented models.
</P>
<DT><TT>--enable-libgcc-rebuild=DIR / --disable-libgcc-rebuild</TT>
<DD><P>This is a grueling temporary hack no matter which way you look
at it. It's described in <A HREF="gccrebuild.html">its own
little page</A>. Note that other --enable flags will
interact with this one. As of libstdc++-v3 snapshot 2.90.8,
this is enabled by default, with DIR
set to <TT> '../..' </TT>, so that building
the complete GCC sources with libstdc++-v3 in place works
transparently.
</P>
<DT><TT>--enable-cxx-flags=FLAGS</TT>
<DD><P>With this option, you can pass a string of -f (functionality)
flags to the compiler to use when building libstdc++. FLAGS
is a quoted string of options, like
<PRE>
--enable-cxx-flags='-fsquangle -fvtable-gc -ansi'</PRE>
Note that the flags don't necessarily have to all be -f flags,
as shown, but usually those are the ones that will make sense
for experimentation and configure-time overriding.
</P>
<P>The advantage of --enable-cxx-flags over setting CXXFLAGS in
the 'make' environment is that, if libgcc is automatically
rebuilt, the same flags will be used when compiling those files
as well, so that everything matches.
</P>
<P>Fun flags to try might include combinations of
<PRE>
-fstrict-aliasing
-fnew-abi
-fnew-exceptions
-ffunction-sections
-fvtable-gc</PRE>
and -fno- forms of the same. Tell us (the mailing list) if
you discover more!
</P>
</DL>
</P>
<P>Return <A HREF="#top">to the top of the README</A> or
<A HREF="index.html">to the homepage</A>.
</P>
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