sh-elf-gcc/README.md

# Automatic `sh-elf-gcc` installer

This script can be used to automatically compile and install a GCC cross-compiler targeting SH3 and SH4 calculators. The normal use is with GiteaPC:

```
% giteapc install Lephenixnoir/sh-elf-gcc
```

You can also install manually. First install [`sh-elf-binutils`](https://gitea.planet-casio.com/Lephenixnoir/sh-elf-binutils), then run the GiteaPC Makefile with a manually-specified install prefix:

```
% make -f giteapc.make configure build install PREFIX=$HOME/.local
```

An `any` configuration is provided in case GCC is already installed externally, to have this package installed without rebuilding it.

```
% giteapc install Lephenixnoir/sh-elf-gcc:any
```

## Notes on building libstdc++-v3

These are experimental notes on attempts at building the C++ standard library implementation bundled with GCC, `libstdc++-v3`. For the official manual, see [libstdc++ info manual, Chapter 2: Setup](https://gcc.gnu.org/onlinedocs/libstdc++/manual/setup.html) (gcc.gnu.org).

So far, I was only able to build the **free-standing subset** which has basically nothing in it, see [Freestanding and hosted implementations](https://en.cppreference.com/w/cpp/freestanding) (cppreference.com). As a rule of thumb only features that look like extensions of the language are supported in there (RTTI, exceptions, coroutines, etc.) and everything that looks like a library (STL containers, I/O tools, filesystem) you can forget about. This subset does not include familiar features but it is needed nonetheless for C++ programs to work at all.

So how do we go around doing that?

First configure GCC as usual (follow `configure.sh`), but use a separate build folder. Since this is experimental the files are likely to stay here longer while debugging and you don't want them gone during a GCC upgrade. There are a couple of additional flags to care about, mainly described [here](https://gcc.gnu.org/onlinedocs/libstdc++/manual/configure.html).

```
% export PREFIX="$(pwd)"
% mkdir build-libstdc++
% cd build-libstdc++
% ../gcc-11.1.0/configure --prefix="$PREFIX" --target=sh3eb-elf --with-multilib-list=m3,m4-nofpu --enable-languages=c,c++ --without-headers --with-newlib --program-prefix=sh-elf- --enable-libssp --enable-lto --enable-clocale=generic --enable-libstdcxx-allocator --disable-threads --disable-hosted-libstdcxx --disable-libstdcxx-verbose --enable-cxx-flags="-ffreestanding -fno-exceptions"
```

* `--enable-clocale=generic`: We want minimal locales and this is certainly the minimalistic option.
* `--enable-libstdcxx-allocator`: `=malloc` might be an option too.
* `--disable-threads`: Obvious.
* `--disable-hosted-libstdcxx`: This builds only the free-standing subset of the library. If you're adventurous, remove it.
* `--disable-libstdcxx-verbose`: We don't have a systematic standard error stream anyway.
* `--enable-cxx-flags="-ffreestanding -fno-exceptions"`: Everything should be free-standing since we don't use a standard runtime.

Currently I don't know of a way to completely disable exceptions in a way that linking with libstdc++ does not include all the stack unwinding and RTTI code for exceptions, but it sure starts with `-fno-exceptions` so it can't hurt to have that.

Now build and install that GCC and the libgcc.

```
% make -j$(nproc) all-gcc all-target-libgcc
% make -j$(nproc) install-strip-gcc install-strip-target-libgcc
```

Next step is to install [OpenLibm](https://gitea.planet-casio.com/Lephenixnoir/OpenLibm) and [fxlibc](https://gitea.planet-casio.com/Vhex-Kernel-Core/fxlibc/) since we're certainly not going to build the C++ standard library without the C standard library.

For some reason OpenLibm installs its headers in the `include/openlibm` subfolder, but then includes them as if they were in `include`, so we have to add a path. Normally either the projet provides that path, or gint does it through its CMake find module. Here we can symlink to the `sh3eb-elf/sys-include` folder in this repo's root folder (or `include` but it's already symlinked to the compiler's install folder and we don't really want to override that).

```
% SRC="$(sh-elf-gcc -print-file-name=include/openlibm)"
% DST="../sh3eb-elf/sys-include"
% mkdir -p "$DST"
% for x in "$SRC"/*.h; do ln -s "$x" "$DST/${x#$SRC/}"; done
```

Also `<stdint.h>` has issues because GCC only redirects to its default `"stdint-gcc.h"` when free-standing, which conftest programs are not, so we have to provide some version of `<stdint.h>`.

```
% echo '#include "stdint-gcc.h"' > ../sh3eb-elf/sys-include/stdint.h
```

After this, come back to the build folder, run the build command for libstdc++-v3, and hope it works out. I recommend not using `-j` as it makes error messages and logs more linear, and the library builds very fast anyway.

```
% make all-target-libstdc++-v3
```

If it fails, check out `sh3eb-elf/libstdc++-v3/config.log` for configure errors, or other log files if you make it past the configuration step. `config.log` has many details on programs that failed to compile; not all failures to build are fatal for the configuration step, but some are.

If it succeeds, install.

```
% make install-strip-target-libstdc++-v3
```

### Current problems

Hard problems:

* None. The free-standing subset compiles.

Things that look like they could be involved in problems:

* Anything that is not in the fxlibc can fail to link.

* The conftest programs are built without `-ffreestanding`, which means autoconf cannot really link stuff. This is probably not too much of a problem, because it's cross-compiled anyway so there's nothing to do with a linked program, but who knows.

* autoconf compiles conftest programs as if on a fully-featured dynamic OS, which is nowhere near true (eg. it builds with `-shared-libgcc`).