forked from mirrors/nixpkgs
4d4f94cde4
One should do this when needed executables at run time. It is more honest and cross-friendly than refering to binutils directly, if one neeeds the default binary tools for the target platform, rather than binutils in particular.
118 lines
4.7 KiB
Nix
118 lines
4.7 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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/* "dfold" a ternary function `op' between successive elements of `list' as if
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it was a doubly-linked list with `lnul' and `rnul` base cases at either
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end. In precise terms, `fold op lnul rnul [x_0 x_1 x_2 ... x_n-1]` is the
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same as
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let
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f_-1 = lnul f_0;
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f_0 = op f_-1 x_0 f_1;
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f_1 = op f_0 x_1 f_2;
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f_2 = op f_1 x_2 f_3;
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...
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f_n = op f_n-1 x_n f_n+1;
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f_n+1 = rnul f_n;
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in
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f_0
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*/
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dfold = op: lnul: rnul: list:
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let
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len = builtins.length list;
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go = pred: n:
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if n == len
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then rnul pred
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else let
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# Note the cycle -- call-by-need ensures finite fold.
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cur = op pred (builtins.elemAt list n) succ;
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succ = go cur (n + 1);
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in cur;
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lapp = lnul cur;
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cur = go lapp 0;
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in cur;
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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.imap1
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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 = nextStage: stageFun: prevStage: let
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args = stageFun prevStage;
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args' = args // {
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stdenv = args.stdenv // {
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# For debugging
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__bootPackages = prevStage;
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__hatPackages = nextStage;
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};
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};
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in
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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 null else prevStage;
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targetPackages = if args.selfBuild or true then null else nextStage;
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});
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# This is a hack for resolving cross-compiled compilers' run-time
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# deps. (That is, compilers that are themselves cross-compiled, as
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# opposed to used to cross-compile packages.)
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postStage = buildPackages: {
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__raw = true;
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stdenv.cc =
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if buildPackages.stdenv.cc.isClang or false
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then buildPackages.clang
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else buildPackages.gcc;
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};
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in dfold folder postStage (_: {}) withAllowCustomOverrides
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