[GHC] #10424: Build path leaks into ABI hashes

17 May 2015

      #10424: Build path leaks into ABI hashes
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              Reporter:  nomeata     |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:
             Component:  Compiler    |           Version:  7.8.4
              Keywords:              |  Operating System:  Unknown/Multiple
          Architecture:              |   Type of failure:  None/Unknown
  Unknown/Multiple                   |        Blocked By:
             Test Case:              |   Related Tickets:
              Blocking:              |
Differential Revisions:              |
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 The build path of GHC leaks into the ABI hashes, i.e. if you build GHC in
 /tmp/fooADDF and then in /tmp/fooSDFS, you get different ABI hashes. This
 is a serious problem for distributions, as it means that we cannot rebuild
 the GHC package without rebuilding all Haskell packages as well.

 The (or at least one) problem is include paths. We have
 {{{
 include-dirs: /home/jojo/build/haskell/ghc/rts/dist/build
               /home/jojo/build/haskell/ghc/includes
               /home/jojo/build/haskell/ghc/includes/dist-
 derivedconstants/header
 }}}
 in `inplace/lib/package.conf.d/builtin_rts.conf`, so when running the
 preprocessor, GHC passes this full path to the preprocessor:
 {{{
 /usr/bin/gcc -E -undef -traditional -DOPTIMISE_INTEGER_GCD_LCM -include
 libraries/base/dist-install/build/autogen/cabal_macros.h -I libraries/base
 /dist-install/build -I libraries/base/dist-install/build -I libraries/base
 /dist-install/build/autogen -I libraries/base/include -I
 /home/jojo/build/haskell/ghc/libraries/integer-gmp/include -I
 /home/jojo/build/haskell/ghc/rts/dist/build -I
 /home/jojo/build/haskell/ghc/includes -I
 /home/jojo/build/haskell/ghc/includes/dist-derivedconstants/header
 '-D__GLASGOW_HASKELL__=711' -include
 /home/jojo/build/haskell/ghc/includes/ghcversion.h '-Dlinux_BUILD_OS=1'
 '-Dx86_64_BUILD_ARCH=1' '-Dlinux_HOST_OS=1' '-Dx86_64_HOST_ARCH=1'
 '-D__GLASGOW_HASKELL_TH__=YES' '-D__SSE__=1' '-D__SSE2__=1' -x assembler-
 with-cpp libraries/base/System/Info.hs -o /tmp/ghc14804_0/ghc14804_1.hscpp
 }}}

 It then reads the included files from the `hscpp` file :
 {{{
 $ grep home /tmp/ghc14830_0/ghc14830_1.hscpp
 # 1 "/home/jojo/build/haskell/ghc/includes/ghcversion.h" 1
 # 1 "/home/jojo/build/haskell/ghc/includes/ghcplatform.h" 1
 }}}
 and puts it into the interface, where it becomes part of the hash:
 {{{
 $ ./inplace/bin/ghc-stage1 --show-iface ./libraries/base/dist-
 install/build/System/Info.hi |grep Dep
 addDependentFile "/home/jojo/build/haskell/ghc/includes/ghcplatform.h"
 addDependentFile "/home/jojo/build/haskell/ghc/includes/ghcversion.h"
 addDependentFile "libraries/base/dist-
 install/build/autogen/cabal_macros.h"
 addDependentFile "/usr/include/stdc-predef.h"
 }}}

 Clearly, the end result is undesirable (changing hashes due to path names)
 and actually useless, as the build path will not be there later anyways.

 I’m not sure what the best way to fix this is. Here are a few ideas:
  * Do not include the path of `addDependentFile` entries in the hash, but
 only the file hash. Should solve the ABI hash.
  * Use relative paths in `inplace/lib/package.conf.d/builtin_rts.conf`.
 Not sure what breaks.

 This bug appeared in 7.8.4 and is present in both 7.10 and current HEAD.

 Any other ideas?

 (Debian bugreport at http://bugs.debian.org/785282)

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10424
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