1 files changed, 40 insertions, 0 deletions
diff --git a/pkgs/development/compilers/gcc/common/checksum.nix b/pkgs/development/compilers/gcc/common/checksum.nix
new file mode 100644
index 00000000000..b3e387b107b
--- /dev/null
+++ b/pkgs/development/compilers/gcc/common/checksum.nix
@@ -0,0 +1,40 @@
+{ lib
+, stdenv
+, nukeReferences
+, langC
+, langCC
+, runtimeShell
+}:
+
+let
+  enableChecksum = (with stdenv; buildPlatform == hostPlatform && hostPlatform == targetPlatform) && langC && langCC;
+in
+(pkg: pkg.overrideAttrs (previousAttrs: lib.optionalAttrs enableChecksum {
+  outputs = previousAttrs.outputs ++ lib.optionals enableChecksum [ "checksum" ];
+  # This is a separate phase because gcc assembles its phase scripts
+  # in bash instead of nix (we should fix that).
+  preFixupPhases = (previousAttrs.preFixupPhases or []) ++ [ "postInstallSaveChecksumPhase" ];
+  #
+  # gcc uses an auxiliary utility `genchecksum` to md5-hash (most of) its
+  # `.o` and `.a` files prior to linking (in case the linker is
+  # nondeterministic).  Since we want to compare across gccs built from two
+  # separate derivations, we wrap `genchecksum` with a `nuke-references`
+  # call.  We also stash copies of the inputs to `genchecksum` in
+  # `$checksum/inputs/` -- this is extremely helpful for debugging since
+  # it's hard to get Nix to not delete the $NIX_BUILD_TOP of a successful
+  # build.
+  #
+  postInstallSaveChecksumPhase = ''
+    mv gcc/build/genchecksum gcc/build/.genchecksum-wrapped
+    cat > gcc/build/genchecksum <<\EOF
+    #!${runtimeShell}
+    ${nukeReferences}/bin/nuke-refs $@
+    for INPUT in "$@"; do install -Dt $INPUT $checksum/inputs/; done
+    exec build/.genchecksum-wrapped $@
+    EOF
+    chmod +x gcc/build/genchecksum
+    rm gcc/*-checksum.*
+    make -C gcc cc1-checksum.o cc1plus-checksum.o
+    install -Dt $checksum/checksums/ gcc/cc*-checksum.o
+  '';
+}))