dontmerge: #209870 (external bootstrap) + #206907 (gcc12) #213931
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Co-authored-by: Weijia Wang <9713184+wegank@users.noreply.github.com>
On a native (host==build==target) build, `${with_build_sysroot}` can
be omitted. In that case, the line modified by this commit is
correct.
However, if `--with-build-sysroot=` is passed to `./configure`, then
`${with_build_sysroot}` will be used, similar to the cross case, and
the headers will be taken from:
${with_build_sysroot}${native_system_header_dir}
See:
https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/configure.ac;h=62bc908b991ff0b700225aef32743cd3d7c4daaf;hb=HEAD#l2439
This commit adjusts the comment to account for the case where
`--with-build-sysroot` is passed to a native compiler.
#### Immediate Benefits
- Allow `gcc11` on `aarch64`
- No more copying `libgcc_s` out of the bootstrap-files or other
derivations
- No more [static `lib{mpfr,mpc,gmp,isl}.a`
hack](https://github.com/NixOS/nixpkgs/blob/2f1948af9c984ebb82dfd618e67dc949755823e2/pkgs/stdenv/linux/default.nix#L380)
- *Zero* additional `gcc` builds (stage1+stage2+stageCompare)
- The `gcc` derivation builds `gcc` once instead of three times.
- The libraries that are linked into the final `pkgs.gcc` (`mpfr`,
`mpc`, `gmp`, `isl`, `glibc`) are built by
`stdenv.__bootPkgs.gcc` rather than by the `bootstrapFiles`. No
more Frankenstein compiler!
- stageCompare runs **concurrently** with (not in series with)
with `stdenv`'s dependees.
- Many other `stdenv` hacks eliminated.
- `gcc` and `clang` share the same codepath for more of
`cc-wrapper`.
- Makes the cross and native codepaths much more similar --
another step towards "cross by default".
Note that *all* the changes in this PR are controlled by flags; no
old codepaths need to be removed until/if we're completely certain
that this is the right way to go.
#### Future Benefits
- This should allow using a [foreign] `bootstrap-files` so long as
`hostPlatform.canExecute bootstrapFiles`.
- There will be an "avalanche of simplification" when we set
`enableGccExternalBootstrap=true` and run dead code elimination.
It's really quite a huge amount of code that goes away.
Native-gcc has its own special codepath in so many places, while
cross-gcc and clang work the same way (and are much simpler).
- This should allow each of the libraries that ship with `gcc`
(`lib{backtrace,atomic,cc1,decnumber,ffi,gomp,iberty,offloadatomic,quadmath,sanitizer,ssp,stdc++-v3,vtv}`)
to be built in separate (one-liner) derivations which `inherit
src;` from `gcc`.
- Building `libstdc++-v3` in a separate derivation will eliminate
a lot of accidental-reference-to-the-`bootstrapFiles` landmines.
#### Incorporates
- #209054
- #210004
- #36948 (unreverted)
- #210325
- #210118
- #210132
- #210109
#### Closes
- Closes #208412
- Closes #108111
- Closes #108305
- Closes #201254
#### Build history
- First successful builds (stage1/stage2):
- powerpc64le-linux at 9c7e9ef256714455914180c0bcb434e014e5b75a
- x86_64-linux at 9c7e9ef256714455914180c0bcb434e014e5b75a
- aarch64-linux at 4d5bc7dabfbe1f8758559390e373b91dda9d401e
- First successful comparisons (stageCompare):
- at 81949cffa3272f8f9bdc8cfda8effb34be517d2f
- [aarch64-linux][aarch64-compare-ofborg]
- [x86\_64-linux][amd64-compare-ofborg]
#### Credits
This project was made possible by three important insights, none of
which were mine:
1. @Ericson2314 was the first to advocate for this change, and
probably the first to appreciate its advantages. External
bootstrap is "cross by default".
2. @trofi has figured out a lot about how to get gcc to not mix up
the copy of `libstdc++` that it depends on with the copy that it
builds. Now that gcc is written in C++, it depends on
`libstdc++`, builds a copy of `libstdc++`, and builds auxiliary
products (like `libplugin`) which depend on `libstdc++`. @trofi
developed two important techniques for keeping this straight: the
use of a [nonexistent sysroot] and moving the `bootstrapFiles`'
`libstdc++` into a [versioned directory]. Without these two
discoveries, external bootstrap would be impossible, because the
final gcc would still have references to the `bootstrapFiles`.
3. Using the undocumented variable [`user-defined-trusted-dirs`]
when building glibc. When glibc `dlopen()`s `libgcc_s.so`, it
uses a completely different and totally special set of rules for
finding `libgcc_s.so`. This trick is the only way we can put
`libgcc_s.so` in its own separate outpath without creating
circular dependencies or dependencies on the bootstrapFiles. I
would never have guessed to use this (or that it existed!) if it
were not for a [comment in guix] which @Mic92 [mentioned].
My own role in this PR was basically: being available to go on a
coding binge at an opportune moment, so we wouldn't waste a
[crisis].
[aarch64-compare-ofborg]: https://github.com/NixOS/nixpkgs/pull/209870/checks?check_run_id=10662822938
[amd64-compare-ofborg]: https://github.com/NixOS/nixpkgs/pull/209870/checks?check_run_id=10662825857
[nonexistent sysroot]: #210004
[versioned directory]: #209054
[`user-defined-trusted-dirs`]: https://sourceware.org/legacy-ml/libc-help/2013-11/msg00026.html
[comment in guix]: https://github.com/guix-mirror/guix/blob/5e4ec8218142eee8e6e148e787381a5ef891c5b1/gnu/packages/gcc.scm#L253
[mentioned]: #210112 (comment)
[crisis]: #108305
[foreign]: #170857 (comment)
GCC searches for headers in:
${with_build_sysroot}${native_system_header_dir}
Ordinarily we set
with_build_sysroot=/
native_system_header_dir="${lib.getDev stdenv.cc.libc}/include"
This commit causes the `xgcc` stage-1 compiler (not the final
compiler) to use a slightly different partitioning:
with_build_sysroot="${lib.getDev stdenv.cc.libc}"
native_system_header_dir="/include"
The concatenated result is the same, but `sysroot` is much easier to
override.
This reverts commit 250c9e5.
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6.topic: emacs
6.topic: kernel
6.topic: stdenv
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@ofborg build stdenv |
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It works! |
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For OfBorg. Merge commits used to bring #206907 up to latest
staging.