From c78686e411e0a14cff51836fe6c35d7584171df3 Mon Sep 17 00:00:00 2001 From: Graham Christensen Date: Fri, 10 May 2019 16:39:31 -0400 Subject: [PATCH] build: run diff-hook under --check and document diff-hook --- .../advanced-topics/advanced-topics.xml | 1 + doc/manual/advanced-topics/diff-hook.xml | 207 ++++++++++++++++++ doc/manual/command-ref/conf-file.xml | 81 ++++++- src/libstore/build.cc | 30 ++- 4 files changed, 303 insertions(+), 16 deletions(-) create mode 100644 doc/manual/advanced-topics/diff-hook.xml diff --git a/doc/manual/advanced-topics/advanced-topics.xml b/doc/manual/advanced-topics/advanced-topics.xml index b710f9f2b..c304367aa 100644 --- a/doc/manual/advanced-topics/advanced-topics.xml +++ b/doc/manual/advanced-topics/advanced-topics.xml @@ -7,5 +7,6 @@ Advanced Topics + diff --git a/doc/manual/advanced-topics/diff-hook.xml b/doc/manual/advanced-topics/diff-hook.xml new file mode 100644 index 000000000..d2613f6df --- /dev/null +++ b/doc/manual/advanced-topics/diff-hook.xml @@ -0,0 +1,207 @@ + + +Verifying Build Reproducibility with <option linkend="conf-diff-hook">diff-hook</option> + +Check build reproducibility by running builds multiple times +and comparing their results. + +Specify a program with Nix's to +compare build results when two builds produce different results. Note: +this hook is only executed if the results are not the same, this hook +is not used for determining if the results are the same. + +For purposes of demonstration, we'll use the following Nix file, +deterministic.nix for testing: + + +let + inherit (import <nixpkgs> {}) runCommand; +in { + stable = runCommand "stable" {} '' + touch $out + ''; + + unstable = runCommand "unstable" {} '' + echo $RANDOM > $out + ''; +} + + +Additionally, nix.conf contains: + + +diff-hook = /etc/nix/my-diff-hook +run-diff-hook = true + + +where /etc/nix/my-diff-hook is an executable +file containing: + + +#!/bin/sh +exec >&2 +echo "For derivation $3:" +/run/current-system/sw/bin/runuser -u nobody -- /run/current-system/sw/bin/diff -r "$1" "$2" + + + + The diff hook can be run as root. Take care to run as little + as possible as root, for this example we use runuser + to drop privileges. + + + + +
+ + Spot-Checking Build Determinism + + + + Verify a path which already exists in the Nix store by passing + to the build command. + + + If the build passes and is deterministic, Nix will exit with a + status code of 0: + + +$ nix-build ./deterministic.nix -A stable +these derivations will be built: + /nix/store/z98fasz2jqy9gs0xbvdj939p27jwda38-stable.drv +building '/nix/store/z98fasz2jqy9gs0xbvdj939p27jwda38-stable.drv'... +/nix/store/yyxlzw3vqaas7wfp04g0b1xg51f2czgq-stable + +$ nix-build ./deterministic.nix -A stable --check +checking outputs of '/nix/store/z98fasz2jqy9gs0xbvdj939p27jwda38-stable.drv'... +/nix/store/yyxlzw3vqaas7wfp04g0b1xg51f2czgq-stable + + + If the build is not deterministic, Nix will exit with a status + code of 1: + + +$ nix-build ./deterministic.nix -A unstable +these derivations will be built: + /nix/store/cgl13lbj1w368r5z8gywipl1ifli7dhk-unstable.drv +building '/nix/store/cgl13lbj1w368r5z8gywipl1ifli7dhk-unstable.drv'... +/nix/store/krpqk0l9ib0ibi1d2w52z293zw455cap-unstable + +$ nix-build ./deterministic.nix -A unstable --check +checking outputs of '/nix/store/cgl13lbj1w368r5z8gywipl1ifli7dhk-unstable.drv'... +error: derivation '/nix/store/cgl13lbj1w368r5z8gywipl1ifli7dhk-unstable.drv' may not be deterministic: output '/nix/store/krpqk0l9ib0ibi1d2w52z293zw455cap-unstable' differs + + +In the Nix daemon's log, we will now see: + +For derivation /nix/store/cgl13lbj1w368r5z8gywipl1ifli7dhk-unstable.drv: +1c1 +< 8108 +--- +> 30204 + + + + Using with + will cause Nix to keep the second build's output in a special, + .check path: + + +$ nix-build ./deterministic.nix -A unstable --check --keep-failed +checking outputs of '/nix/store/cgl13lbj1w368r5z8gywipl1ifli7dhk-unstable.drv'... +note: keeping build directory '/tmp/nix-build-unstable.drv-0' +error: derivation '/nix/store/cgl13lbj1w368r5z8gywipl1ifli7dhk-unstable.drv' may not be deterministic: output '/nix/store/krpqk0l9ib0ibi1d2w52z293zw455cap-unstable' differs from '/nix/store/krpqk0l9ib0ibi1d2w52z293zw455cap-unstable.check' + + + In particular, notice the + /nix/store/krpqk0l9ib0ibi1d2w52z293zw455cap-unstable.check + output. Nix has copied the build results to that directory where you + can examine it. + + + <literal>.check</literal> paths are not registered store paths + + Check paths are not protected against garbage collection, + and this path will be deleted on the next garbage collection. + + The path is guaranteed to be alive for the duration of + 's execution, but may be deleted + any time after. + + If the comparison is performed as part of automated tooling, + please use the diff-hook or author your tooling to handle the case + where the build was not deterministic and also a check path does + not exist. + + + + is only usable if the derivation has + been built on the system already. If the derivation has not been + built Nix will fail with the error: + +error: some outputs of '/nix/store/hzi1h60z2qf0nb85iwnpvrai3j2w7rr6-unstable.drv' are not valid, so checking is not possible + + + Run the build without , and then try with + again. + +
+ +
+ + Automatic and Optionally Enforced Determinism Verification + + + + Automatically verify every build at build time by executing the + build multiple times. + + + + Setting and + in your + nix.conf permits the automated verification + of every build Nix performs. + + + + The following configuration will run each build three times, and + will require the build to be deterministic: + + +enforce-determinism = true +repeat = 2 + + + + + Setting to false as in + the following configuration will run the build multiple times, + execute the build hook, but will allow the build to succeed even + if it does not build reproducibly: + + +enforce-determinism = false +repeat = 1 + + + + + An example output of this configuration: + +$ nix-build ./test.nix -A unstable +these derivations will be built: + /nix/store/ch6llwpr2h8c3jmnf3f2ghkhx59aa97f-unstable.drv +building '/nix/store/ch6llwpr2h8c3jmnf3f2ghkhx59aa97f-unstable.drv' (round 1/2)... +building '/nix/store/ch6llwpr2h8c3jmnf3f2ghkhx59aa97f-unstable.drv' (round 2/2)... +output '/nix/store/6xg356v9gl03hpbbg8gws77n19qanh02-unstable' of '/nix/store/ch6llwpr2h8c3jmnf3f2ghkhx59aa97f-unstable.drv' differs from '/nix/store/6xg356v9gl03hpbbg8gws77n19qanh02-unstable.check' from previous round +/nix/store/6xg356v9gl03hpbbg8gws77n19qanh02-unstable + + +
+ diff --git a/doc/manual/command-ref/conf-file.xml b/doc/manual/command-ref/conf-file.xml index f0da1f612..a1a5d6e12 100644 --- a/doc/manual/command-ref/conf-file.xml +++ b/doc/manual/command-ref/conf-file.xml @@ -1,7 +1,9 @@ + + xml:id="sec-conf-file" + version="5"> nix.conf @@ -240,6 +242,64 @@ false. + diff-hook + + + Absolute path to an executable capable of diffing build results. + The hook executes if is + true, and the output of a build is known to not be the same. + This program is not executed to determine if two results are the + same. + + + + + The root user executes the diff hook in a daemonised + installation. See for + information on using the diff hook safely. + + + + The diff hook program receives three parameters: + + + + + A path to the previous build's results + + + + + + A path to the current build's results + + + + + + The path to the build's derivation + + + + + The diff hook should not print data to stderr or stdout, as + output is not displayed to the user. However, if information is + printed, it will be printed in the nix-daemon + log. + + When using the Nix daemon, diff-hook must + be set in the nix.conf configuration file, and + cannot be passed at the command line. + + + + + + enforce-determinism + + See . + + extra-sandbox-paths @@ -595,9 +655,9 @@ password my-password they are deterministic. The default value is 0. If the value is non-zero, every build is repeated the specified number of times. If the contents of any of the runs differs from the - previous ones, the build is rejected and the resulting store paths - are not registered as “valid” in Nix’s database. - + previous ones and is + true, the build is rejected and the resulting store paths are not + registered as “valid” in Nix’s database. require-sigs @@ -628,6 +688,19 @@ password my-password + run-diff-hook + + + If true, enable the execution of . + + + + When using the Nix daemon, run-diff-hook must + be set in the nix.conf configuration file, + and cannot be passed at the command line. + + + sandbox diff --git a/src/libstore/build.cc b/src/libstore/build.cc index 91eb97dfb..026828c53 100644 --- a/src/libstore/build.cc +++ b/src/libstore/build.cc @@ -461,6 +461,19 @@ static void commonChildInit(Pipe & logPipe) close(fdDevNull); } +void handleDiffHook(Path tryA, Path tryB, Path drvPath) +{ + auto diffHook = settings.diffHook; + if (diffHook != "" && settings.runDiffHook) { + try { + auto diff = runProgram(diffHook, true, {tryA, tryB, drvPath}); + if (diff != "") + printError(chomp(diff)); + } catch (Error & error) { + printError("diff hook execution failed: %s", error.what()); + } + } +} ////////////////////////////////////////////////////////////////////// @@ -3039,8 +3052,7 @@ void DerivationGoal::registerOutputs() InodesSeen inodesSeen; Path checkSuffix = ".check"; - bool runDiffHook = settings.runDiffHook; - bool keepPreviousRound = settings.keepFailed || runDiffHook; + bool keepPreviousRound = settings.keepFailed || settings.runDiffHook; std::exception_ptr delayedException; @@ -3185,11 +3197,14 @@ void DerivationGoal::registerOutputs() if (!worker.store.isValidPath(path)) continue; auto info = *worker.store.queryPathInfo(path); if (hash.first != info.narHash) { + handleDiffHook(path, actualPath, drvPath); + if (settings.keepFailed) { Path dst = worker.store.toRealPath(path + checkSuffix); deletePath(dst); if (rename(actualPath.c_str(), dst.c_str())) throw SysError(format("renaming '%1%' to '%2%'") % actualPath % dst); + throw Error(format("derivation '%1%' may not be deterministic: output '%2%' differs from '%3%'") % drvPath % path % dst); } else @@ -3254,16 +3269,7 @@ void DerivationGoal::registerOutputs() ? fmt("output '%1%' of '%2%' differs from '%3%' from previous round", i->second.path, drvPath, prev) : fmt("output '%1%' of '%2%' differs from previous round", i->second.path, drvPath); - auto diffHook = settings.diffHook; - if (prevExists && diffHook != "" && runDiffHook) { - try { - auto diff = runProgram(diffHook, true, {prev, i->second.path}); - if (diff != "") - printError(chomp(diff)); - } catch (Error & error) { - printError("diff hook execution failed: %s", error.what()); - } - } + handleDiffHook(prev, i->second.path, drvPath); if (settings.enforceDeterminism) throw NotDeterministic(msg);