bf17d6dacf
[N.B., this package also applies to the commits that follow it in the same
PR.]
In most cases, buildPackages = pkgs so things work just as before. For
cross compiling, however, buildPackages is resolved as the previous
bootstrapping stage. This allows us to avoid the mkDerivation hacks cross
compiling currently uses today.
To avoid a massive refactor, callPackage will splice together both package
sets. Again to avoid churn, it uses the old `nativeDrv` vs `crossDrv` to do
so. So now, whether cross compiling or not, packages with get a `nativeDrv`
and `crossDrv`---in the non-cross-compiling case they are simply the same
derivation. This is good because it reduces the divergence between the
cross and non-cross dataflow. See `pkgs/top-level/splice.nix` for a comment
along the lines of the preceding paragraph, and the code that does this
splicing.
Also, `forceNativeDrv` is replaced with `forceNativePackages`. The latter
resolves `pkgs` unless the host platform is different from the build
platform, in which case it resolves to `buildPackages`. Note that the
target platform is not important here---it will not prevent
`forcedNativePackages` from resolving to `pkgs`.
--------
Temporarily, we make preserve some dubious decisions in the name of preserving
hashes:
Most importantly, we don't distinguish between "host" and "target" in the
autoconf sense. This leads to the proliferation of *Cross derivations
currently used. What we ought to is resolve native deps of the cross "build
packages" (build = host != target) package set against the "vanilla
packages" (build = host = target) package set. Instead, "build packages"
uses itself, with (informally) target != build in all cases.
This is wrong because it violates the "sliding window" principle of
bootstrapping stages that shifting the platform triple of one stage to the
left coincides with the next stage's platform triple. Only because we don't
explicitly distinguish between "host" and "target" does it appear that the
"sliding window" principle is preserved--indeed it is over the reductionary
"platform double" of just "build" and "host/target".
Additionally, we build libc, libgcc, etc in the same stage as the compilers
themselves, which is wrong because they are used at runtime, not build
time. Fixing this is somewhat subtle, and the solution and problem will be
better explained in the commit that does fix it.
Commits after this will solve both these issues, at the expense of breaking
cross hashes. Native hashes won't be broken, thankfully.
--------
Did the temporary ugliness pan out? Of the packages that currently build in
`release-cross.nix`, the only ones that have their hash changed are
`*.gcc.crossDrv` and `bootstrapTools.*.coreutilsMinimal`. In both cases I
think it doesn't matter.
1. GCC when doing a `build = host = target = foreign` build (maximally
cross), still defines environment variables like `CPATH`[1] with
packages. This seems assuredly wrong because whether gcc dynamically
links those, or the programs built by gcc dynamically link those---I
have no idea which case is reality---they should be foreign. Therefore,
in all likelihood, I just made the gcc less broken.
2. Coreutils (ab)used the old cross-compiling infrastructure to depend on
a native version of itself. When coreutils was overwritten to be built
with fewer features, the native version it used would also be
overwritten because the binding was tight. Now it uses the much looser
`BuildPackages.coreutils` which is just fine as a richer build dep
doesn't cause any problems and avoids a rebuild.
So, in conclusion I'd say the conservatism payed off. Onward to actually
raking the muck in the next PR!
[1]: https://gcc.gnu.org/onlinedocs/gcc/Environment-Variables.html
75 lines
3.4 KiB
Nix
75 lines
3.4 KiB
Nix
# This file defines a single function for booting a package set from a list of
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# stages. The exact mechanics of that function are defined below; here I
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# (@Ericson2314) wish to describe the purpose of the abstraction.
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#
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# The first goal is consistency across stdenvs. Regardless of what this function
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# does, by making every stdenv use it for bootstrapping we ensure that they all
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# work in a similar way. [Before this abstraction, each stdenv was its own
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# special snowflake due to different authors writing in different times.]
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#
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# The second goal is consistency across each stdenv's stage functions. By
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# writing each stage it terms of the previous stage, commonalities between them
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# are more easily observable. [Before, there usually was a big attribute set
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# with each stage, and stages would access the previous stage by name.]
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#
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# The third goal is composition. Because each stage is written in terms of the
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# previous, the list can be reordered or, more practically, extended with new
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# stages. The latter is used for cross compiling and custom
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# stdenvs. Additionally, certain options should by default apply only to the
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# last stage, whatever it may be. By delaying the creation of stage package sets
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# until the final fold, we prevent these options from inhibiting composition.
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#
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# The fourth and final goal is debugging. Normal packages should only source
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# their dependencies from the current stage. But for the sake of debugging, it
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# is nice that all packages still remain accessible. We make sure previous
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# stages are kept around with a `stdenv.__bootPackges` attribute referring the
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# previous stage. It is idiomatic that attributes prefixed with `__` come with
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# special restrictions and should not be used under normal circumstances.
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{ lib, allPackages }:
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# Type:
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# [ pkgset -> (args to stage/default.nix) or ({ __raw = true; } // pkgs) ]
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# -> pkgset
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#
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# In english: This takes a list of function from the previous stage pkgset and
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# returns the final pkgset. Each of those functions returns, if `__raw` is
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# undefined or false, args for this stage's pkgset (the most complex and
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# important arg is the stdenv), or, if `__raw = true`, simply this stage's
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# pkgset itself.
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#
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# The list takes stages in order, so the final stage is last in the list. In
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# other words, this does a foldr not foldl.
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stageFuns: let
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# Take the list and disallow custom overrides in all but the final stage,
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# and allow it in the final flag. Only defaults this boolean field if it
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# isn't already set.
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withAllowCustomOverrides = lib.lists.imap
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(index: stageFun: prevStage:
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# So true by default for only the first element because one
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# 1-indexing. Since we reverse the list, this means this is true
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# for the final stage.
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{ allowCustomOverrides = index == 1; }
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// (stageFun prevStage))
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(lib.lists.reverseList stageFuns);
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# Adds the stdenv to the arguments, and sticks in it the previous stage for
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# debugging purposes.
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folder = stageFun: finalSoFar: let
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args = stageFun finalSoFar;
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args' = args // {
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stdenv = args.stdenv // {
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# For debugging
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__bootPackages = finalSoFar;
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};
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};
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self =
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if args.__raw or false
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then args'
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else allPackages ((builtins.removeAttrs args' ["selfBuild"]) // {
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buildPackages = if args.selfBuild or true then self else finalSoFar;
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});
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in self;
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in lib.lists.fold folder {} withAllowCustomOverrides
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