Okay to clarify newlib is only the C library right? I'm using the
gcc-arm-none-eabi-9-2019-q4 toolchain which it seems it comes with
newlib libc but as far as I know I'm not linking to it. Furthermore
I'm interesting in std C++11 functionality for portability not just
the the C++11 dialect.
About libcxx it seems to be only working partially with my current
toolchain (gcc-arm-none-eabi-9-2019-q4):
With minimal testing I'm already getting these problems:
- iostream gives linker errors with locale e.g. "multiple definition
of `duplocale'"
- optional.cxx doesn't compile, although disabling it can compile further
- linking with libsupc++ gives linker errors e.g.
"std::set_unexpected(void (*)())'"
- GCC9 requires to enable fpermissive CXX flags
Do I have to use another toolchain? (Although NuttX getting started
guide is reffering to gcc-arm-none-eabi-9) or do I have to downgrade
my NuttX kernel (libcxx hasn't seen any update in 2-3 years maybe that
has to do with?)
Many parts of newlib are not compatible with the NuttX C library. If
you link them together, you asking for some nasty surprises down the
road. For example, what is the binary representation of type FILE? I
guarantee the two representations are not compatible. What if a newlib
functions receives a NuttX argument of type FILE (or vise versa)? I was
expect a crash.
Of course, many things will work. Like string manipulation functions
and probably the math library (people use the newlib math library, but
that has never been proven to be safe). The fact that many things from
the binary incompatbile newlib work lulls people into believing it is a
technically viable solution. It is not.
Certainly if you are mixing incompatible binaries you are creating an
unsafe system. I would not think such a think could ever be flight or
safety certifiable.
In order to avoid binary incompatibly, all libraries must be linked with
only code from the NuttX C library (and nothing from newlib). The C++
standard library must be created by compiling it with header files from
the NuttX C library.
Currently, the *only* toolchain that does that correctly is the NuttX
buildroot toolchain: https://bitbucket.org/nuttx/buildroot/src/master/
It does not contain newlib and imports the NuttX header files when it
builds. So it is 100% newlib free. It is a pure NuttX tools chaing.
The binary that it generates is an arm-nuttx-eabi-gcc toolchain. Ff you
create the C++ standard library using these header files, it is
guaranteed to be 100% binary compatible.
Most people ignore this good advice. I think that they do not grasp the
incredible risk that they are taking.
Greg
