libtool insistence upon -fno-rtti -fno-exceptions in libsupc++?

[Ned Konz <ned at bike-nomad dot com>]

Hi there,

I'm attempting to build libstdc++ for the Atmel AVR family, which is  
an 8-bit microcontroller.
This is in a freestanding environment that's got somewhat limited  
memory space
(the biggest part has 4K of RAM, and the smallest supported by gcc  
has 64 bytes of RAM).

As a result, I'm compiling this as a freestanding library,
and I suspect that most people will be using "-fno-exceptions -fno- 
rtti" in their compilation.

However, (assuming there's no penalty for doing so when you use those  
flags),
I have no problems making the exception handling and RTTI available  
in the library.
Similarly, I wouldn't care if I had to compile the library without  
them, at least for right now.

I'm working from the HEAD of the gcc (4.2.0beta?) svn sources.

avr-gcc and avr-libc work fine, and I have no problems compiling them.

However, when the compilation gets to libsupc++,
I have problems with libtool insisting upon using "-fno-rtti -fno- 
exceptions" to compile code that uses "typeid", which then fails the  
compilation.

I did not ask for "-fno-rtti -fno-exceptions".

I did originally try using "-fno-exceptions" in the --enable-cxx- 
flags config argument, but had the same problem,
so I removed it and re-configured and tried building again. No  
improvement.

I'm configuring using:
====
prefix=/opt/local
crossgccTarget=avr
version=4.2-20060429
${srcdir}/configure  \
        --prefix=${prefix} \
        --infodir="${prefix}/share/info" \
        --mandir="${prefix}/share/man" \
        --target=${crossgccTarget} \
        --program-prefix=${crossgccTarget}- \
        --with-included-gettext \
        --with-gxx-include-dir=${prefix}/${crossgccTarget}/include/c+ 
+/${version}/ \
        --disable-libssp \
        --disable-nls \
        --disable-symvers \
        --disable-hosted-libstdcxx \
        --disable-threads \
        --enable-cstdio=stdio \
        --enable-libstdcxx-allocator=malloc \
        --disable-long-long --disable-wchar_t \
        --enable-sjlj-exceptions \
        --enable-languages=c++ \
        --with-sysroot=${prefix}/${crossgccTarget} \
        "$@"
====

and I then build using:
====
AR_FOR_TARGET=avr-ar \
AS_FOR_TARGET=avr-as \
LD_FOR_TARGET=avr-ld \
NM_FOR_TARGET=avr-nm \
RANLIB_FOR_TARGET=avr-ranlib \
gmake -w "$@"
====

What I get from the compilation ends with:
====
gmake[2]: Entering directory `/Users/ned/src/avr-gcc/build/avr/libstdc 
++-v3'
Making all in include
/Users/ned/src/avr-gcc/build/avr/libstdc++-v3/include
gmake[3]: Entering directory `/Users/ned/src/avr-gcc/build/avr/libstdc 
++-v3/include'
gmake[3]: Nothing to be done for `all'.
gmake[3]: Leaving directory `/Users/ned/src/avr-gcc/build/avr/libstdc+ 
+-v3/include'
Making all in libsupc++
/Users/ned/src/avr-gcc/build/avr/libstdc++-v3/libsupc++
gmake[3]: Entering directory `/Users/ned/src/avr-gcc/build/avr/libstdc 
++-v3/libsupc++'
/bin/sh ../libtool --tag CXX --tag disable-shared --mode=compile / 
Users/ned/src/avr-gcc/build/./gcc/xgcc -shared-libgcc -B/Users/ned/ 
src/avr-gcc/build/./gcc -nostdinc++ -L/Users/ned/src/avr-gcc/build/ 
avr/libstdc++-v3/src -L/Users/ned/src/avr-gcc/build/avr/libstdc++-v3/ 
src/.libs -B/opt/local/avr/    bin/ -B/opt/local/avr/lib/ -isystem / 
opt/local/avr/include -isystem /opt/local/avr/sys-include -I/  Users/ 
ned/src/avr-gcc/gcc/libstdc++-v3/../gcc -I/Users/ned/src/avr-gcc/ 
build/avr/libstdc++-v3/      include/avr -I/Users/ned/src/avr-gcc/ 
build/avr/libstdc++-v3/include -I/Users/ned/src/avr-gcc/gcc/   libstdc 
++-v3/libsupc++  -fno-implicit-templates  -Wall -Wextra -Wwrite- 
strings -Wcast-qual  -       fdiagnostics-show-location=once    -g - 
O2   -c -o eh_exception.lo ../../../../gcc/libstdc++-v3/     libsupc+ 
+/eh_exception.cc
/Users/ned/src/avr-gcc/build/./gcc/xgcc -shared-libgcc -B/Users/ned/ 
src/avr-gcc/build/./gcc -       nostdinc++ -L/Users/ned/src/avr-gcc/ 
build/avr/libstdc++-v3/src -L/Users/ned/src/avr-gcc/build/avr/   
libstdc++-v3/src/.libs -B/opt/local/avr/bin/ -B/opt/local/avr/lib/ - 
isystem /opt/local/avr/include -isystem /opt/local/avr/sys-include -I/ 
Users/ned/src/avr-gcc/gcc/libstdc++-v3/../gcc -I/Users/ned/   src/avr- 
gcc/build/avr/libstdc++-v3/include/avr -I/Users/ned/src/avr-gcc/build/ 
avr/libstdc++-v3/     include -I/Users/ned/src/avr-gcc/gcc/libstdc++- 
v3/libsupc++ -fno-implicit-templates -Wall -Wextra - Wwrite-strings - 
Wcast-qual -fdiagnostics-show-location=once -g -O2 -c ../../../../gcc/ 
libstdc++-v3/ libsupc++/eh_exception.cc -o eh_exception.o
../../../../gcc/libstdc++-v3/libsupc++/eh_exception.cc: In member  
function 'virtual const char*     std::exception::what() const':
../../../../gcc/libstdc++-v3/libsupc++/eh_exception.cc:42: error:  
cannot use typeid with -fno-rtti
gmake[3]: *** [eh_exception.lo] Error 1
gmake[3]: Leaving directory `/Users/ned/src/avr-gcc/build/avr/libstdc+ 
+-v3/libsupc++'
gmake[2]: *** [all-recursive] Error 1
gmake[2]: Leaving directory `/Users/ned/src/avr-gcc/build/avr/libstdc+ 
+-v3'
gmake[1]: *** [all] Error 2
gmake[1]: Leaving directory `/Users/ned/src/avr-gcc/build/avr/libstdc+ 
+-v3'
gmake: *** [all-target-libstdc++-v3] Error 2
gmake: Leaving directory `/Users/ned/src/avr-gcc/build'
====

If I use -k with make, I see that the same problem also exists with:

libstdc++-v3/libsupc++/tinfo2.cc

Earlier, libtool or configure (I'm not sure which) had said (among  
other things)...
====
checking if /Users/ned/src/avr-gcc/build/./gcc/xgcc supports -fno- 
rtti -fno-exceptions ... yes
checking whether the linker (/Users/ned/src/avr-gcc/build/./gcc/ 
collect-ld) supports shared         libraries... no
checking how to hardcode library paths into programs... immediate
checking whether stripping libraries is possible... yes
checking dynamic linker characteristics... no
checking command to parse /Users/ned/src/avr-gcc/build/./gcc/nm  
output... failed
checking if libtool supports shared libraries... no
checking whether to build shared libraries... no
checking whether to build static libraries... yes
appending configuration tag "CXX" to libtool
configure: Only freestanding libraries will be built
checking for exception model to use... sjlj
====

I'm sure I'm doing something wrong; the build system is more than a  
little complicated and I haven't wanted to try to figure the whole  
thing out yet.

Can anyone give me some guidance here?

Thanks,
--
Ned Konz
MetaMagix embedded consulting
MetaMagix@gmail.com