96 lines
4.4 KiB
Nix
96 lines
4.4 KiB
Nix
{ lib
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, stdenv
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, langC
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, langCC
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, langJit
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}:
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let
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enableLibGccOutput = (with stdenv; targetPlatform == hostPlatform) && !langJit && !stdenv.hostPlatform.isDarwin;
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in
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(pkg: pkg.overrideAttrs (previousAttrs: lib.optionalAttrs ((!langC) || langJit || enableLibGccOutput) {
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outputs = previousAttrs.outputs ++ lib.optionals enableLibGccOutput [ "libgcc" ];
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# This is a separate phase because gcc assembles its phase scripts
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# in bash instead of nix (we should fix that).
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preFixupPhases = (previousAttrs.preFixupPhases or []) ++ [ "preFixupLibGccPhase" ];
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preFixupLibGccPhase =
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# delete extra/unused builds of libgcc_s in non-langC builds
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# (i.e. libgccjit, gnat, etc) to avoid potential confusion
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lib.optionalString (!langC) ''
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rm -f $out/lib/libgcc_s.so*
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''
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# TODO(amjoseph): remove the `libgcc_s.so` symlinks below and replace them
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# with a `-L${gccForLibs.libgcc}/lib` in cc-wrapper's
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# `$out/nix-support/cc-flags`. See also:
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# - https://github.com/NixOS/nixpkgs/pull/209870#discussion_r1130614895
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# - https://github.com/NixOS/nixpkgs/pull/209870#discussion_r1130635982
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# - https://github.com/NixOS/nixpkgs/commit/404155c6acfa59456aebe6156b22fe385e7dec6f
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#
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# move `libgcc_s.so` into its own output, `$libgcc`
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+ lib.optionalString enableLibGccOutput (''
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# move libgcc from lib to its own output (libgcc)
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mkdir -p $libgcc/lib
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mv $lib/lib/libgcc_s.so $libgcc/lib/
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mv $lib/lib/libgcc_s.so.1 $libgcc/lib/
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ln -s $libgcc/lib/libgcc_s.so $lib/lib/
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ln -s $libgcc/lib/libgcc_s.so.1 $lib/lib/
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''
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#
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# Nixpkgs ordinarily turns dynamic linking into pseudo-static linking:
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# libraries are still loaded dynamically, exactly which copy of each
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# library is loaded is permanently fixed at compile time (via RUNPATH).
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# For libgcc_s we must revert to the "impure dynamic linking" style found
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# in imperative software distributions. We must do this because
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# `libgcc_s` calls `malloc()` and therefore has a `DT_NEEDED` for `libc`,
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# which creates two problems:
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#
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# 1. A circular package dependency `glibc`<-`libgcc`<-`glibc`
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#
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# 2. According to the `-Wl,-rpath` flags added by Nixpkgs' `ld-wrapper`,
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# the two versions of `glibc` in the cycle above are actually
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# different packages. The later one is compiled by this `gcc`, but
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# the earlier one was compiled by the compiler *that compiled* this
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# `gcc` (usually the bootstrapFiles). In any event, the `glibc`
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# dynamic loader won't honor that specificity without namespaced
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# manual loads (`dlmopen()`). Once a `libc` is present in the address
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# space of a process, that `libc` will be used to satisfy all
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# `DT_NEEDED`s for `libc`, regardless of `RUNPATH`s.
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#
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# So we wipe the RUNPATH using `patchelf --set-rpath ""`. We can't use
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# `patchelf --remove-rpath`, because at least as of patchelf 0.15.0 it
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# will leave the old RUNPATH string in the file where the reference
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# scanner can still find it:
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#
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# https://github.com/NixOS/patchelf/issues/453
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#
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# Note: we might be using the bootstrapFiles' copy of patchelf, so we have
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# to keep doing it this way until both the issue is fixed *and* all the
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# bootstrapFiles are regenerated, on every platform.
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#
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# This patchelfing is *not* effectively equivalent to copying
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# `libgcc_s` into `glibc`'s outpath. There is one minor and one
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# major difference:
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#
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# 1. (Minor): multiple builds of `glibc` (say, with different
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# overrides or parameters) will all reference a single store
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# path:
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#
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# /nix/store/xxx...xxx-gcc-libgcc/lib/libgcc_s.so.1
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#
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# This many-to-one referrer relationship will be visible in the store's
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# dependency graph, and will be available to `nix-store -q` queries.
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# Copying `libgcc_s` into each of its referrers would lose that
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# information.
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#
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# 2. (Major): by referencing `libgcc_s.so.1`, rather than copying it, we
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# are still able to run `nix-store -qd` on it to find out how it got
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# built! Most importantly, we can see from that deriver which compiler
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# was used to build it (or if it is part of the unpacked
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# bootstrap-files). Copying `libgcc_s.so.1` from one outpath to
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# another eliminates the ability to make these queries.
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#
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+ ''
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patchelf --set-rpath "" $libgcc/lib/libgcc_s.so.1
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'');
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}))
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