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  1. Swift
  2. SR-6508

rpath order is inconsistent between Darwin and Linux

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    Details

    • Type: Bug
    • Status: Closed
    • Priority: Medium
    • Resolution: Done
    • Component/s: Compiler
    • Labels:
    • Environment:

      Swift 4.0.2

      Description

      On Darwin, the swift compiler takes care to place its own rpath (the location of the swift standard library) after any user-specified rpaths. https://github.com/apple/swift/blob/cdab55a202154f031386463fcce83bde11d5f3b2/lib/Driver/ToolChains.cpp#L1132-L1160

      On Linux this is not the case

      To reproduce, start from a new executable package (swift package init --type executable) (called test), and build with

      swift build -Xlinker -rpath -Xlinker /usr/local/lib

      On macOS this produces a binary with a runtime library search path containing 2 entries, as follows:

      • /usr/local/lib (the user-provided search path)
      • the location of the swift standard library

      To observe this use otool -l as follows:

      $ swift build -Xlinker -rpath -Xlinker /usr/local/lib
      Linking ./.build/x86_64-apple-macosx10.10/debug/test
      $ otool -l ./.build/debug/test
      ...
      Load command 18
                cmd LC_RPATH
            cmdsize 32
               path /usr/local/lib (offset 12)
      Load command 19
                cmd LC_RPATH
            cmdsize 112
               path /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/macosx (offset 12)
      ...
      

      On Linux this same command produces a binary whose runtime library search path has 3 entries, as follows:

      • the location of the swift standard library
      • /usr/local/lib (the user-provided search path)
      • $ORIGIN, a symbol indicating the directory containing the binary (similar to Darwin's @executable_path).

      This can be observed with the readelf command:

      $ readelf -d ./.build/debug/test
      ...
       0x000000000000001d (RUNPATH)            Library runpath: [/usr/lib/swift/linux:/usr/local/lib:$ORIGIN]
      

      It seems strange that the Linux version gives a different order than the Darwin one, I would expect the order to be consistent across platforms. Furthermore, I think the Darwin order is the correct one as it allows each layer to override a lower one (a swiftPM user can override swiftPM's authors which in turn can override swiftc). It's possible that on Darwin, SwiftPM should also insert @executable_path between user-specified search paths and compiler-specified ones.

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            • Assignee:
              keith Keith Smiley
              Reporter:
              ksweeney Kevin Sweeney
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              • Created:
                Updated:
                Resolved: