This commit allows `gccCrossStageStatic` to build dynamically-linked
libraries. Since is no longer restricted to building static
libraries its name is no longer appropriate, and this commit also
renames it to the more-accurate `gccWithoutTargetLibc`.
By default, you can't build a gcc that knows how to create dynamic
libraries unless you have already built the targetPlatform libc.
Because of this, our gcc cross-compiler is built in two stages:
1. Build a cross-compiler (gccCrossStageStatic) that can build
only static libraries.
2. Use gccCrossStageStatic to compile the targetPlatform libc.
3. Use the targetPlatform libc to build a fully-capable cross
compiler.
You might notice that this pattern looks very similar to what we do
with `xgcc` in the stdenv bootstrap. Indeed it is! I would like to
work towards getting the existing stdenv bootstrap to handle cross
compilers as well. However we don't want to cripple `stdenv.xgcc`
by taking away its ability to build dynamic libraries.
It turns out that the only thing gcc needs the targetPlatform libc
for is to emit a DT_NEEDED for `-lc` into `libgcc.so`. That's it!
And since we don't use `gccCrossStageStatic` to build anything other
than libc, it's safe to omit the `DT_NEEDED` because that `libgcc`
will never be loaded by anything other than `libc`. So `libc` will
already be in the process's address space.
Other people have noticed this; crosstool-ng has been using this
approach for a very long time:
36ad0b17a7/scripts/build/cc/gcc.sh (L638-L640)
Upstream `gcc-13` merged `mcfgthreads` support with a caveat: it's
headers interface is not compatible with the patch `nixpkgs` was
carrying in `gcc-12` and before.
To keep both new (`gcc13`) and old (`_pre_gcc13`) version I held back
previous `windows.mcfgthreads` attribute as
`windows.mcfgthreads_pre_gcc_13`. It is used for `gcc` before 13.
The change fixes the build of `pkgsCross.mingwW64.stdenv` itself and
example program:
$ nix build --impure --expr 'with import ./. {}; pkgsCross.mingwW64.re2c.override { stdenv = pkgsCross.mingwW64.gcc11Stdenv; }'
This will begin the process of breaking up the `useLLVM` monolith. That
is good in general, but I hope will be good for NetBSD and Darwin in
particular.
Co-authored-by: sterni <sternenseemann@systemli.org>
