gcc/common: add disableGdbPlugin option #216237
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trofi
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LGTM. Can you add a single sentence for commit description where it could be useful?
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Sorry about that, fixed now. |
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Apart from one flag inversion the change looks good.
Can you add a 1-sentence Why motivation description as well? A few reasons I could make up are:
- cut down on build times (does it save a lot?)
- does the default value cause some other problems during bootstrap? (which? extra depends? something probes it? some c++-specific failures?)
- just a handy switch to flip to debug some gcc aspect?
- something else?
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Squashed, with a more detailed commmit message explaining the motivation. This raises the question of whether or not the behavior which causes us to need Also, since libcc1 is considered unmaintained there would have to be a decision about whether the benefit of a fix upstream is worth the risk of breaking things that nobody is particularly motivated to fix. |
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Ah, early linking of libstdc++ makes sense. Yeah, disabling it early if needed is the simplest.
Generally, I saw the --with-stage1-libs= flag that might allow a similar kind of tweaking. But it's probably more fragile as it needs an exhaustive (AFAIU) list of libraries upfront.
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Worth removing added assert? It should be fine to disable both.
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Dammit, that should be !enablePlugin. Thank you for noticing.
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Dammit, that should be !enablePlugin. Thank you for noticing.
This commit adds an option `disableGdbPlugin` which controls whether or not the plugin *for* GDB will be built. This plugin contains a copy of `gcc`. The configure flag that this option controls is called `--disable-libcc1`. This flag name is slightly confusing: it is used only by GDB (and apparently unmaintained), yet the flag name does not mention GDB. This is why the option name is different from the configure flag name. The primary motivation for this commit is to allow the following PR (which is not yet merged) to pass `--disable-libcc1` when building the final native (build=host=target) compiler as part of the stdenv bootstrap: #209870 We need to `--disable-libcc1` in this scenario because gcc's build machinery links `libcc1` against the `libstdc++` that is part of the *compiler used to compile gcc*, rather than against the `libstdc++` that is built *by* gcc. In an FHS distribution this distinction is not terribly important because dynamically linked libraries are late-bound (ld.so resolution). However in nixpkgs this causes a reference back to the bootstrapFiles to leak all the way through to the final stdenv. More details can be found in the comment in `pkgs/stdenv/linux/default.nix` of the PR linked above. Co-authored-by: Sandro <sandro.jaeckel@gmail.com>
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Dammit, I messed this up again: |
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Caused #342904 |
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#### Summary
By default, when you type `make`, GCC will compile itself three
times. This PR inhibits that behavior by configuring GCC with
`--disable-bootstrap`, and reimplements the triple-rebuild using
Nix rather than `make`/`sh`.
#### Immediate Benefits
- Allow `gcc11` and `gcc12` on `aarch64` (without needing new
`bootstrapFiles`)
- Faster stdenv rebuilds: the third compilation of gcc
(i.e. stageCompare) is no longer a `drvInput` of the final stdenv.
This allows Nix to build stageCompare in parallel with the rest of
nixpkgs instead of in series.
- No more copying `libgcc_s` out of the bootstrap-files or other
derivations
- No more Frankenstein compiler: the final gcc and the libraries it
links against (mpfr, mpc, isl, glibc) are all built by the same
compiler (xgcc) instead of a mixture of the bootstrapFiles'
compiler and xgcc.
- No more [static lib{mpfr,mpc,gmp,isl}.a hack]
- Many other small `stdenv` hacks eliminated
- `gcc` and `clang` share the same codepath for more of `cc-wrapper`.
#### Future Benefits
- This should allow using a [foreign] `bootstrap-files` so long as
`hostPlatform.canExecute bootstrapFiles`.
- 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`, much like NixOS/nixpkgs#132343
#### Incorporates
- NixOS/nixpkgs#210004
- NixOS/nixpkgs#36948 (unreverted)
- NixOS/nixpkgs#210325
- NixOS/nixpkgs#210118
- NixOS/nixpkgs#210132
- NixOS/nixpkgs#210109
- NixOS/nixpkgs#213909
- NixOS/nixpkgs#216136
- NixOS/nixpkgs#216237
- NixOS/nixpkgs#210019
- NixOS/nixpkgs#216232
- NixOS/nixpkgs#216016
- NixOS/nixpkgs#217977
- NixOS/nixpkgs#217995
#### Closes
- Closes #108305
- Closes #108111
- Closes #201254
- Closes #208412
#### 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. Nix-driven
(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, by moving the `bootstrapFiles`' `libstdc++` into a
[versioned directory]. This allows a Nix-driven bootstrap of gcc
without the final gcc would still having 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]: NixOS/nixpkgs#210004
[versioned directory]: NixOS/nixpkgs#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]: NixOS/nixpkgs#210112 (comment)
[crisis]: NixOS/nixpkgs#108305
[foreign]: NixOS/nixpkgs#170857 (comment)
[static lib{mpfr,mpc,gmp,isl}.a hack]: https://github.com/NixOS/nixpkgs/blob/2f1948af9c984ebb82dfd618e67dc949755823e2/pkgs/stdenv/linux/default.nix#L380
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Description of changes
gcc/common: add disableGdbPlugin option
This commit adds an option
disableGdbPluginwhich controls whetheror not the plugin for GDB, which contains a copy of
gcc, will bebuilt.
The configure flag that this option controls is called
--disable-libcc1. This is slightly confusing, because its is usedonly by GDB (and apparently unmaintained), yet its name does not
mention GDB. This is why the option name is different from the
configure flag name.
Things done
sandbox = trueset innix.conf? (See Nix manual)nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage./result/bin/)