debian/README.source

   1 Document by Ximin Luo, Luca Bruno & Sylvestre Ledru
   2
   3 This source package is unfortunately quite tricky and with several cutting
   4 edges, due to the complexity of rust-lang bootstrapping system and the high
   5 rate of language changes still ongoing.
   6
   7 We try to describe here inner packaging details and the reasons behind them.
   8
   9 If you are looking to help maintain this package, be sure to read the "Notes
  10 for package maintainers" section further below.
  11
  12
  13 Embedded libraries
  14 ==================
  15
  16 The upstream source package embeds many external libraries. We make a great
  17 effort to remove them and use system versions where possible, but there are a
  18 few more remaining:
  19
  20  * vendor/dlmalloc, vendor/windows_*_gnu, vendor/windows_*_msvc
  21
  22    These are small C libraries designed to be statically linked; their upstream
  23    does not support building them as a shared library and they are too small to
  24    justify their own Debian package.
  25
  26
  27 Building from source
  28 ====================
  29
  30 The Debian rustc package will use the system rustc to bootstrap itself from.
  31 The system rustc has to be either the previous or the same version as the rustc
  32 being built; the build will fail if this is not the case.
  33
  34     sudo apt-get build-dep ./
  35     dpkg-buildpackage
  36     # Or, to directly use what's in the Debian FTP archive
  37     sudo apt-get build-dep rustc
  38     apt-get source --compile rustc
  39
  40 Alternatively, you may give the "pkg.rustc.dlstage0" DEB_BUILD_PROFILE to
  41 instead use the process defined by Rust upstream. This downloads the "official"
  42 stage0 compiler for the version being built from rust-lang.org. At the time of
  43 writing "official" means "the previous stable version".
  44
  45     sudo apt-get build-dep -P pkg.rustc.dlstage0 ./
  46     dpkg-buildpackage -P pkg.rustc.dlstage0
  47     # Or, to directly use what's in the Debian FTP archive
  48     sudo apt-get build-dep -P pkg.rustc.dlstage0 rustc
  49     apt-get source --compile -P pkg.rustc.dlstage0 rustc
  50
  51 After [1] is fixed, both of these should in theory give identical results.
  52
  53 If neither of these options are acceptable to you, e.g. because your distro
  54 does not have rustc already and your build process cannot access the network,
  55 see "Bootstrapping" below.
  56
  57 [1] https://github.com/rust-lang/rust/issues/34902
  58
  59
  60 Bootstrapping
  61 =============
  62
  63 To bootstrap rustc on a distro that does not have it or cargo available on any
  64 architecture (so cross-compiling is not an option) you can run `debian/rules
  65 source_orig-stage0`. This creates a .dsc that does not Build-Depend on rustc or
  66 cargo. Instead, it includes an extra orig-stage0 source tarball that contains
  67 the official stage0 compiler, pre-downloaded from rust-lang.org so that your
  68 build daemons don't need to access the network during the build.
  69
  70     debian/rules source_orig-stage0
  71     # Follow the final manual instructions that it outputs. Then:
  72     sbuild ../rustc_*.dsc && dput ../rustc_*.dsc
  73
  74 To only bootstrap specific architectures, run this instead:
  75
  76     upstream_bootstrap_arch="arm64 armhf" debian/rules source_orig-stage0
  77
  78 This way, other architectures will be omitted from the orig-stage0 tarball. You
  79 might want to do this e.g. if these other architectures are already present in
  80 your distro, but the $upstream_bootstrap_arch ones are not yet present.
  81
  82 Notes
  83 -----
  84
  85 The approach bundles the upstream bootstrapping binaries inside the Debian
  86 source package. This is a nasty hack that stretches the definition of "source
  87 package", but has a few advantages explained below.
  88
  89 The traditional Debian way of bootstrapping compilers - and other distros have
  90 similar approaches - is some variant of the following:
  91
  92 1. A developer locally installs some upstream bootstrapping binaries.
  93 2. They locally build a Debian package, using these binaries as undeclared
  94    build dependencies.
  95 3. They upload these binary packages to Debian, which can be used as declared
  96    Build-Depends in the future, including by the same package.
  97
  98 The problem with this is, Debian does not have any policy nor infrastructure
  99 that can try to reproduce what this developer supposedly did.
 100
 101 Using bootstrapping binary blobs *at some point of the process* is unavoidable.
 102 Rather than pretending we didn't do this, it is better to record *which blobs*
 103 we used, so it can be audited later. If we bundle non-Debian build-dependencies
 104 inside the source package, then we can do a *source-only upload*, and the
 105 building of the binary packages can be done by the normal build infrastructure.
 106
 107 If the build process is reproducible [1] then we can be sure that *you* (as the
 108 developer that prepared the source-only upload) didn't backdoor the binaries,
 109 nor did the build daemons even if they were compromised during the build.
 110
 111 The bootstrapping binaries may still have been backdoored, but this is true in
 112 both scenarios. So our arrangement is still a strict improvement in security,
 113 because it reduces the set of "things that may have been backdoored". Also,
 114 more people use the upstream binaries than the "magical original Debian
 115 package", so backdoors have a greater chance of being detected in the former.
 116
 117 In the long run, this process is laying the foundations for doing Diverse
 118 Double-Compilation [2], where we use *many independent* bootstrapping binaries
 119 to reproduce bit-for-bit identical output compilers, giving confidence that
 120 nothing was backdoored along the way.
 121
 122 [1] The build process for rustc is currently *not* reproducible but we're
 123     working towards it. https://github.com/rust-lang/rust/issues/34902
 124 [2] http://www.dwheeler.com/trusting-trust/
 125
 126
 127 Maintaining this package
 128 ========================
 129
 130 Import of a new upstream version
 131 --------------------------------
 132
 133 $ apt install equivs python3-magic
 134 $ sudo mk-build-deps -irt 'aptitude -R'
 135 $ uscan --verbose                       # or debian/rules source_orig-beta, for beta
 136 $ ver=UPDATE-ME                         # whatever it is, probably X.YY.Z or X.YY.Z~beta.N
 137
 138 $ debian/refresh-early-patches.sh $ver
 139 # This will require an understanding of how git-rebase and git-mergetool works
 140 # We recommend either kdiff3 or p4merge (proprietary) as the git-mergetool.
 141
 142 $ tar xf ../rustc-${ver/\~/-}-src.tar.xz && ( cd rustc-${ver/*~*/beta}-src/ && pwd && ../debian/prune-unused-deps ) && rm -rf rustc-${ver/*~*/beta}-src/
 143 $ git diff
 144 # Review the diff. If it removes too much stuff, it could mean that rustc
 145 # pulled in new unnecessary dependencies in this newer version. See if you can
 146 # drop them by amending the patch "d-0000-ignore-removed-submodules.patch".
 147 # Rerun the above "tar ..." commands again and check that your patch works.
 148 # For example, there is absolutely no reason why rustc should need openssl.
 149
 150 $ git commit -m "Update Files-Excluded for new upstream version ${ver/\~/-}" debian/copyright
 151 $ uscan --verbose                       # yes, again, to pick up the new Files-Excluded stuff
 152                                         # or debian/rules source_orig-beta, for beta
 153
 154 # Keep running this and follow its instructions, until it gives no output:
 155 $ debian/check-orig-suspicious.sh $ver
 156 # When you are satisfied with the above, proceed:
 157
 158 $ git checkout debian/experimental
 159 $ gbp import-orig ../rustc_$ver+dfsg1.orig.tar.xz
 160 $ dch -v $ver+dfsg1-1~exp1 "New upstream release."
 161 $ debian/rules update-version
 162 # might also need to bump the version of the cargo Build-Depends
 163 # then refresh patches, etc etc
 164 # Use /usr/share/cargo/scripts/guess-crate-copyright to help update d/copyright quickly
 165
 166 # If you need to repack again, bump the 'repacksuffix' in d/watch then run
 167 $ uscan --verbose --force-download
 168 # This will do a local repack using the new Files-Excluded rules, without
 169 # redownloading the orig tarball (despite the slightly misleading flag).
 170
 171
 172 Proceeding after build failure
 173 ------------------------------
 174
 175 If your build fails, don't run `./x.py` directly as that will detect it's being
 176 run with different settings, and run the build from scratch all over again.
 177 overwriting all intermediate files. Instead, do:
 178
 179 $ debian/rules run_rustbuild X_CMD="build|test|install" X_FLAGS="whatever"
 180
 181 Hopefully, this will directly proceed to the step that failed, without
 182 rebuilding everything in between.
 183
 184
 185 Comparing Debian rustc vs upstream rustc
 186 ----------------------------------------
 187
 188 This package does things the Debian way, which differs significantly from
 189 upstream practices. If you find a bug, you might want to check if it is present
 190 in the upstream package. Run "debian/rules debian/config.toml" to generate our
 191 config.toml that you can then use in an upstream directory **unpacked from the
 192 release tarball*. (It is more complex to get this working with their git repo.)
 193
 194 This will configure it in a "halfway" style between upstream and Debian.
 195 Specifically, it will not build LLVM nor download stuff from crates.io, yet
 196 Debian patches are *not* applied. These specific settings were chosen as a
 197 tradeoff between convenience vs being close to what upstream does - so that the
 198 chances of a bug here being a genuine upstream issue rather than a Debian bug,
 199 is much higher. Also, with the exception of LLVM, these are non-default modes
 200 *supported by* upstream so they would be happy to receive bug reports about it
 201 even if your issue only occurs here.
 202
 203 OTOH if you need to test a completely clean upstream build, including all the
 204 annoying stuff like building LLVM and downloading dependencies from crates.io,
 205 simply unpack the tarball and run `./configure && ./x.py build` etc as normal.
 206 This can be useful for confirming that an issue is caused by Debian's LLVM.
 207
 208 If you need to test a LLVM patch, do something like this:
 209
 210 # build your patched LLVM debs, then:
 211 $ mkdir -p llvm-destdir && cd llvm-destdir
 212 $ ver=4.0; VERSION=FIXME
 213 $ for i in llvm-$ver llvm-$ver-dev llvm-$ver-runtime llvm-$ver-tools libllvm$ver; do \
 214     dpkg -x ../"$i"_*${VERSION}_*.deb .; done
 215 $ cd ../rustc
 216 $ debian/rules LLVM_DESTDIR=$PWD/../llvm-destdir build
 217
 218 If you need to test a patch to the stage0 rustc, do something like this:
 219
 220 # build your patched rustc debs or upstream rustc, then:
 221 $ mkdir -p rust-destdir && cd rust-destdir
 222 $ ver=1.20; VERSION=FIXME;
 223 $ for i in rustc libstd-rust-$ver libstd-rust-dev; do \
 224     dpkg -x ../"$i"_*${VERSION}_*.deb .; done
 225 $ cd ../rustc
 226 $ debian/rules RUST_DESTDIR=$PWD/../rust-destdir build
 227
 228
 229 Useful links
 230 ------------
 231
 232 The Fedora rust team is more active than the Debian one. Here are their links:
 233
 234 Source code
 235 https://src.fedoraproject.org/rpms/rust/tree/
 236
 237 Binary packages and test logs
 238 https://kojipkgs.fedoraproject.org//packages/rust/
 239 If the same test fails both on Fedora and Debian it's a good indication that
 240 we're not Doing It Wrong and can file a valid bug upstream.