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 free-standing subset of 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).

This is 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.

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"
```

* `--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 (one thing at a time).
* `--disable-libstdcxx-verbose`: We don't have a systematic standard error stream anyway.
* `--enable-cxx-flags="-ffreestanding"`: Really everything should be free-standing here. It doesn't apply to conftest programs apparently, which (fail to) link with the default C runtime (`crt1.o` etc), maybe something will need to be done about that in the future.

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
```

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.

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

Since this will likely fail, 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.

### Current problems

Hard limits:

* `<stdio.h>` is not complete yet.

Suspected problems:

* 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`).