[staging] stdenv: trim random seed to avoid reference cycles #106954
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cc @andir would appreciate your thoughts on this - hoping to get this fixed soon since it is breaking a good number of cross packages |
andir
reviewed
Dec 23, 2020
| @@ -1,4 +1,7 @@ | |||
| # Use the last part of the out path as hash input for the build. | |||
| # This should ensure that it is deterministic across rebuilds of the same | |||
| # derivation and not easily collide with other builds. | |||
| export NIX_CFLAGS_COMPILE+=" -frandom-seed=${out##*/}" | |||
| # We also truncate the hash so that it cannot cause reference cycles. | |||
| local outbase="${out##*/}" | |||
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Does local really just span this file? Setup hooks are sourced via stdenv, right?
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Ah I think you are right. How about putting this in a getRandomSeed function? I can't just inline the basename + trimming because bash won't do the nested expansion
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Ok, I ended up using a command substitution. Looks a little odd but avoids any namespace pollution
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On 13:24 23.12.20, r-burns wrote:
@r-burns commented on this pull request.
> @@ -1,4 +1,7 @@
# Use the last part of the out path as hash input for the build.
# This should ensure that it is deterministic across rebuilds of the same
# derivation and not easily collide with other builds.
-export NIX_CFLAGS_COMPILE+=" -frandom-seed=${out##*/}"
+# We also truncate the hash so that it cannot cause reference cycles.
+local outbase="${out##*/}"
+local randomseed="${outbase:0:10}"
I was a little concerned that the seed is the same for all files, but gcc recommends each file has a unique seed. Is it important for the seed to differ for each build too?
Our initial assesment was that it is enough if it differs per build and
that is exactly what the drv hash gives us.
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Using the full store hash as the random seed occasionally caused reference cycles when the invocation was stored in output artifacts. For example, cross-compiled gcc was failing due to this: https://hydra.nixos.org/eval/1631713#tabs-now-fail Simply truncating the hash is sufficient to avoid this.
r-burns
changed the title
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cc @dezgeg as you are the maintainer for release-cross.nix bootstrapTools |
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Using the full store hash as the random seed occasionally caused
reference cycles when the compiler invocation was stored in output artifacts.
For example, cross-compiled gcc was failing due to this:
https://hydra.nixos.org/eval/1631713#tabs-now-fail
Simply truncating the hash is sufficient to avoid this.
cc @symphorien: #102251 (comment)
Motivation for this change
Things done
sandboxinnix.confon non-NixOS linux)nix-shell -p nixpkgs-review --run "nixpkgs-review wip"./result/bin/)nix path-info -Sbefore and after)