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2affd455a4
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:
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|---|---|---|
| .. | ||
| checksum.nix | ||
| configure-flags.nix | ||
| dependencies.nix | ||
| extra-target-flags.nix | ||
| libgcc.nix | ||
| meta.nix | ||
| platform-flags.nix | ||
| pre-configure.nix | ||
| strip-attributes.nix | ||