tests-stdenv-gcc-stageCompare: cleanup

[tie]

Description of changes

Minor cleanup of the tests-stdenv-gcc-stageCompare. Note that the test itself is currently silently broken, see #314920 (comment). This PR does not fix that.

Parent PR:

• wrapCC, wrapBintools: use absolute paths #314920

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.11 Release Notes (or backporting 23.11 and 24.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[SuperSandro2000]

That's a bit out of scope for my level of knowledge regarding bootstrapping

[tie]

@SuperSandro2000, OK, sorry for the ping. I’m relatively new to the Nix community so I don’t know much about other members’ area of expertise. Do you happen to know someone else who can properly review this? Would be nice if someone was willing to work on fixing this test case since I’m currently out of capacity for low-level stdenv stuff with #314920 and other PRs 😅

[tie]

@wegank, could you help me with triaging this PR? Who is responsible for this part of Nixpkgs? The author of the original PR #209870 deleted GitHub account (amjoseph-nixpkgs)…

Should I move #314920 (comment) to a standalone issue?

[wegank]

@trofi

[trofi]

The change looks fine.

My suggestion would be to remove stageCompare and corresponding checksum handling completely as it does not do what gcc's own do-compare does.

gcc's do-compare validates identity generated code between stage1 built with default value of -fchecking / -g (usually -fchecking=0 -g2) and -fchecking=1 -gtoggle (usually -fchecking=1 -g0). This finds real code generator bugs, like recent https://gcc.gnu.org/PR112107, https://gcc.gnu.org/PR112379, https://gcc.gnu.org/PR113445.

Side note: NIX_OUTPATH_USED_AS_RANDOM_SEED = cc.out; is needed to make the seed of built cc identical to seed of builder cc to make them closer. Otherwise they will be different as the default is randSeed=${NIX_OUTPATH_USED_AS_RANDOM_SEED:-$out}. I agree this seeding should probably not be $out-dependent. I personally use the patch below (and a few others) locally to make binary outputs more stable across minor gcc changes:

--- a/pkgs/build-support/setup-hooks/reproducible-builds.sh
+++ b/pkgs/build-support/setup-hooks/reproducible-builds.sh
@@ -8,2 +8,3 @@ NIX_CFLAGS_COMPILE="${NIX_CFLAGS_COMPILE:-} -frandom-seed=$(
     randomseed="${outbase:0:10}"
+    randomseed=not-random-at-all
     echo $randomseed