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 This source package embeds several external libraries (foeked and managed
  17 by rust upstream as git submodules).
  18 In early stages, many more libraries were forked/emebedded but we are steadily
  19 progressing in splitting them out.
  20
  21 Here below the remaining ones, with the technical reasons.
  22
  23  * jemalloc from https://github.com/rust-lang/jemalloc
  24    -> system-wide one can't be used due to rust using a "je_" prefix.
  25
  26    This is intentional upstream design and won't change soon, see:
  27     - https://github.com/rust-lang/rust/pull/18678
  28     - http://smallcultfollowing.com/babysteps/blog/2014/11/14/allocators-in-rust/
  29
  30  * compiler-rt from https://github.com/rust-lang/compiler-rt
  31    -> system-wide compiler-rt fails during linkage
  32
  33    Bug reported upstream, still to be fixed, see:
  34     - https://github.com/rust-lang/rust/issues/15054
  35     - https://github.com/rust-lang/rust/issues/15708
  36
  37 As a summary, we plan to:
  38  * keep embedding jemalloc (probably forever)
  39  * work with upstream to fix compiler-rt linkage soon.
  40
  41  -- Sylvestre Ledru <sylvestre@debian.org>  Sat, 06 May 2017 13:26:08 +0200
  42
  43
  44 Building from source
  45 ====================
  46
  47 The Debian rustc package will use the system rustc to bootstrap itself from.
  48 The system rustc has to be either the previous or the same version as the rustc
  49 being built; the build will fail if this is not the case.
  50
  51     sudo apt-get build-dep ./
  52     dpkg-buildpackage
  53     # Or, to directly use what's in the Debian FTP archive
  54     sudo apt-get build-dep rustc
  55     apt-get source --compile rustc
  56
  57 Alternatively, you may give the "pkg.rustc.dlstage0" DEB_BUILD_PROFILE to
  58 instead use the process defined by Rust upstream. This downloads the "official"
  59 stage0 compiler for the version being built from rust-lang.org. At the time of
  60 writing "official" means "the previous stable version".
  61
  62     sudo apt-get build-dep -P pkg.rustc.dlstage0 ./
  63     dpkg-buildpackage
  64     # Or, to directly use what's in the Debian FTP archive
  65     sudo apt-get build-dep -P pkg.rustc.dlstage0 rustc
  66     apt-get source --compile -P pkg.rustc.dlstage0 rustc
  67
  68 After [1] is fixed, both of these should in theory give identical results.
  69
  70 If neither of these options are acceptable to you, e.g. because your distro
  71 does not have rustc already and your build process cannot access the network,
  72 see "Bootstrapping" below.
  73
  74 [1] https://github.com/rust-lang/rust/issues/34902
  75
  76
  77 Bootstrapping
  78 =============
  79
  80 To bootstrap rustc on a distro that does not have it or cargo available on any
  81 architecture (so cross-compiling is not an option) you can run `debian/rules
  82 source_orig-stage0`. This creates a .dsc that does not Build-Depend on rustc or
  83 cargo. Instead, it includes an extra orig-stage0 source tarball that contains
  84 the official stage0 compiler, pre-downloaded from rust-lang.org so that your
  85 build daemons don't need to access the network during the build.
  86
  87     debian/rules source_orig-stage0
  88     # Follow the final manual instructions that it outputs. Then:
  89     sbuild ../rustc_*.dsc && dput ../rustc_*.dsc
  90
  91 To only bootstrap specific architectures, run this instead:
  92
  93     upstream_bootstrap_arch="arm64 armhf" debian/rules source_orig-stage0
  94
  95 This way, other architectures will be omitted from the orig-stage0 tarball. You
  96 might want to do this e.g. if these other architectures are already present in
  97 your distro, but the $upstream_bootstrap_arch ones are not yet present.
  98
  99 Notes
 100 -----
 101
 102 The approach bundles the upstream bootstrapping binaries inside the Debian
 103 source package. This is a nasty hack that stretches the definition of "source
 104 package", but has a few advantages explained below.
 105
 106 The traditional Debian way of bootstrapping compilers - and other distros have
 107 similar approaches - is some variant of the following:
 108
 109 1. A developer locally installs some upstream bootstrapping binaries.
 110 2. They locally build a Debian package, using these binaries as undeclared
 111    build dependencies.
 112 3. They upload these binary packages to Debian, which can be used as declared
 113    Build-Depends in the future, including by the same package.
 114
 115 The problem with this is, Debian does not have any policy nor infrastructure
 116 that can try to reproduce what this developer supposedly did.
 117
 118 Using bootstrapping binary blobs *at some point of the process* is unavoidable.
 119 Rather than pretending we didn't do this, it is better to record *which blobs*
 120 we used, so it can be audited later. If we bundle non-Debian build-dependencies
 121 inside the source package, then we can do a *source-only upload*, and the
 122 building of the binary packages can be done by the normal build infrastructure.
 123
 124 If the build process is reproducible [1] then we can be sure that *you* (as the
 125 developer that prepared the source-only upload) didn't backdoor the binaries,
 126 nor did the build daemons even if they were compromised during the build.
 127
 128 The bootstrapping binaries may still have been backdoored, but this is true in
 129 both scenarios. So our arrangement is still a strict improvement in security,
 130 because it reduces the set of "things that may have been backdoored". Also,
 131 more people use the upstream binaries than the "magical original Debian
 132 package", so backdoors have a greater chance of being detected in the former.
 133
 134 In the long run, this process is laying the foundations for doing Diverse
 135 Double-Compilation [2], where we use *many independent* bootstrapping binaries
 136 to reproduce bit-for-bit identical output compilers, giving confidence that
 137 nothing was backdoored along the way.
 138
 139 [1] The build process for rustc is currently *not* reproducible but we're
 140     working towards it. https://github.com/rust-lang/rust/issues/34902
 141 [2] http://www.dwheeler.com/trusting-trust/
 142
 143
 144 Maintaining this package
 145 ========================
 146
 147 Import of a new upstream version
 148 --------------------------------
 149
 150 $ uscan --verbose
 151 $ ver=UPDATE-ME # whatever it is, X.YY.0 probably
 152 $ tar xf ../rustc-$ver-src.tar.gz && ( cd rustc-$ver-src/ && ../debian/prune-unused-deps ) && rm -rf rustc-$ver-src/
 153 # ^ If this fails, you probably need to refresh patches or edit debian/prune-unused-deps
 154 $ git commit -m "Update Files-Excluded for new upstream version $ver" debian/copyright
 155 $ uscan --verbose # yes, again, to pick up the new Files-Excluded stuff
 156
 157 # Keep running this and follow its instructions, until it gives no output:
 158 $ debian/check-orig-suspicious.sh $ver
 159 # When you are satisfied with the above, proceed:
 160
 161 $ gbp import-orig ../rustc_$ver+dfsg1.orig.tar.xz
 162 $ dch -v $ver+dfsg1-1 -m "New upstream release."
 163 $ debian/rules update-version
 164 # might also need to bump the version of the cargo Build-Depends
 165 # then refresh patches, etc etc
 166
 167 # If you need to repack again, bump the 'repacksuffix' in d/watch then run
 168 $ uscan --verbose --force-download
 169 # This will do a local repack using the new Files-Excluded rules, without
 170 # redownloading the orig tarball (despite the slightly misleading flag).
 171
 172
 173 Proceeding after build failure
 174 ------------------------------
 175
 176 If your build fails, don't run `./x.py` directly as that will detect it's being
 177 run with different settings, and run the build from scratch all over again.
 178 overwriting all intermediate files. Instead, do:
 179
 180 $ debian/rules run_rustbuild X_CMD="build|test|install" X_FLAGS="whatever"
 181
 182 Hopefully, this will directly proceed to the step that failed, without
 183 rebuilding everything in between.
 184
 185
 186 Comparing Debian rustc vs upstream rustc
 187 ----------------------------------------
 188
 189 This package does things the Debian way, which differs significantly from
 190 upstream practices. If you find a bug, you might want to check if it is present
 191 in the upstream package. Run "debian/rules debian/configure-upstream" to
 192 generate a script, that you can then run in an unpacked upstream directory.
 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 $ for i in llvm-4.0 llvm-4.0-dev llvm-4.0-runtime llvm-4.0-tools libllvm4.0; do \
 213     dpkg -x ../"$i"_*${VERSION}_*.deb .; done
 214 $ cd ../rustc
 215 $ debian/rules LLVM_DESTDIR=$PWD/../llvm-destdir build
 216
 217
 218 Useful links
 219 ------------
 220
 221 The Fedora rust team is more active than the Debian one. Here are their links:
 222
 223 Source code
 224 https://src.fedoraproject.org/cgit/rpms/rust.git/tree/
 225
 226 Binary packages and test logs
 227 https://kojipkgs.fedoraproject.org//packages/rust/
 228 If the same test fails both on Fedora and Debian it's a good indication that
 229 we're not Doing It Wrong and can file a valid bug upstream.
 230
 231 Package metadata
 232 https://admin.fedoraproject.org/pkgdb/package/rpms/rust/