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redundant linker flag warning is wrong and breaks linking #47989

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redundant linker flag warning is wrong and breaks linking#47989
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A-linkageArea: linking into static, shared libraries and binariesC-bugCategory: This is a bug.

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@wthrowe
wthrowe
opened on Feb 3, 2018

If one passes the same -lfoo option twice to rustc it warns redundant linker flag specified for library `foo` and ignores the second argument. Linkers are sensitive to the order of their arguments and passing the same argument twice is common and sometimes necessary to get a program to link correctly.

In fact, rustc itself passes the linker (cleaned up a bit) -ldl -lrt -lpthread -lpthread -lgcc_s -lc -lm -lrt -lpthread -lutil -lutil, which includes four "redundant" linker flags (at least two of which are actually redundant, to be fair).

Activity

  1. Mark-Simulacrum
    self-assigned this
    on Feb 4, 2018
  2. Mark-Simulacrum
    added
    A-linkageArea: linking into static, shared libraries and binaries
    C-bugCategory: This is a bug.
    on Feb 4, 2018
  3. Mark-Simulacrum
    removed their assignment
    on Feb 4, 2018

  4. Mark-Simulacrum commented on Feb 4, 2018

    @Mark-Simulacrum
    Mark-Simulacrum
    on Feb 4, 2018
    Member

    This is somewhat not trivial to fix as we don't know whether a given -l flag was passed with the purpose of changing the link kind or name, or actually passing the same library twice for linkage. This branch has the initial workings of a viable idea, but it doesn't pass tests.

    There are also to an extent some backwards compatibility concerns here.

    ---- [run-pass] run-pass/rfc1717/library-override.rs stdout ----

error: compilation failed!
status: exit code: 101
command: "/home/mark/Build/rust/build/x86_64-unknown-linux-gnu/stage1/bin/rustc" "/home/mark/Build/rust/src/test/run-pass/rfc1717/library-override.rs" "-L" "/home/mark/Build/rust/build/x86_64-unknown-linux-gnu/test/run-pass" "--target=x86_64-unknown-linux-gnu" "-C" "prefer-dynamic" "-o" "/home/mark/Build/rust/build/x86_64-unknown-linux-gnu/test/run-pass/rfc1717/library-override.stage1-x86_64-unknown-linux-gnu" "-Crpath" "-O" "-Zmiri" "-Zunstable-options" "-Lnative=/home/mark/Build/rust/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-lstatic=wronglibrary:rust_test_helpers" "-L" "/home/mark/Build/rust/build/x86_64-unknown-linux-gnu/test/run-pass/rfc1717/library-override.stage1-x86_64-unknown-linux-gnu.aux"
stdout:
------------------------------------------

------------------------------------------
stderr:
------------------------------------------
error: linking with `cc` failed: exit code: 1
  |
  = note: "cc" "-Wl,--as-needed" "-Wl,-z,noexecstack" "-m64" "-L" "/home/mark/Build/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib" "/home/mark/Build/rust/build/x86_64-unknown-linux-gnu/test/run-pass/rfc1717/library-override.library_override0-317d481089b8c8fe83113de504472633.rs.rcgu.o" "/home/mark/Build/rust/build/x86_64-unknown-linux-gnu/test/run-pass/rfc1717/library-override.library_override1-317d481089b8c8fe83113de504472633.rs.rcgu.o" "-o" "/home/mark/Build/rust/build/x86_64-unknown-linux-gnu/test/run-pass/rfc1717/library-override.stage1-x86_64-unknown-linux-gnu" "/home/mark/Build/rust/build/x86_64-unknown-linux-gnu/test/run-pass/rfc1717/library-override.crate.allocator.rcgu.o" "-Wl,--gc-sections" "-pie" "-Wl,-z,relro,-z,now" "-Wl,-O1" "-nodefaultlibs" "-L" "/home/mark/Build/rust/build/x86_64-unknown-linux-gnu/test/run-pass" "-L" "/home/mark/Build/rust/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/home/mark/Build/rust/build/x86_64-unknown-linux-gnu/test/run-pass/rfc1717/library-override.stage1-x86_64-unknown-linux-gnu.aux" "-L" "/home/mark/Build/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,-Bstatic" "-Wl,--whole-archive" "-l" "rust_test_helpers" "-Wl,--no-whole-archive" "-Wl,--whole-archive" "-l" "rust_test_helpers" "-Wl,--no-whole-archive" "-L" "/home/mark/Build/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,-Bdynamic" "-l" "std-57fdceb1c52b4db2" "-Wl,-Bstatic" "/home/mark/Build/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcompiler_builtins-136e26942e0df602.rlib" "-Wl,-Bdynamic" "-l" "dl" "-l" "rt" "-l" "pthread" "-l" "pthread" "-l" "gcc_s" "-l" "c" "-l" "m" "-l" "rt" "-l" "pthread" "-l" "util" "-l" "util" "-Wl,-rpath,$ORIGIN/../../../stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,-rpath,/home/mark/Build/rust/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,--enable-new-dtags"
  = note: /home/mark/Build/rust/build/x86_64-unknown-linux-gnu/native/rust-test-helpers/librust_test_helpers.a(rust_test_helpers.o): In function `rust_dbg_extern_identity_u32':
          rust_test_helpers.c:(.text.rust_dbg_extern_identity_u32+0x0): multiple definition of `rust_dbg_extern_identity_u32'
          /home/mark/Build/rust/build/x86_64-unknown-linux-gnu/native/rust-test-helpers/librust_test_helpers.a(rust_test_helpers.o):rust_test_helpers.c:(.text.rust_dbg_extern_identity_u32+0x0): first defined here
          /home/mark/Build/rust/build/x86_64-unknown-linux-gnu/native/rust-test-helpers/librust_test_helpers.a(rust_test_helpers.o): In function `rust_dbg_extern_identity_u64':
          rust_test_helpers.c:(.text.rust_dbg_extern_identity_u64+0x0): multiple definition of `rust_dbg_extern_identity_u64'
          /home/mark/Build/rust/build/x86_64-unknown-linux-gnu/native/rust-test-helpers/librust_test_helpers.a(rust_test_helpers.o):rust_test_helpers.c:(.text.rust_dbg_extern_identity_u64+0x0): first defined here
...

  5. lovesegfault commented on Oct 11, 2018

    @lovesegfault
    lovesegfault
    on Oct 11, 2018
    Contributor

    Could we perhaps at least add some option to ignore this?

  6. dcreager commented on Dec 20, 2018

    @dcreager
    dcreager
    on Dec 20, 2018
    Contributor

    I was recently bitten by this bug, trying to link multiple internal helper C++ libraries into a Rust executable. I was able to put together a minimal repro: on Linux, one of the subpackages builds successfully, and one gets linker errors, and the only difference between the two is the order in which the helper libraries are built and added to the linker command line.

  7. dcreager commented on Dec 21, 2018

    @dcreager
    dcreager
    on Dec 21, 2018
    Contributor

    I wrote up a potential fix in #57018. We'd still remove redundant -l flags from the linker command, but instead of keeping the first one, we'd now keep the last one. The new behavior passes CI, and I've verified (via cargo +local build) that it also fixes all of the linker errors in my repro repo.

  8. rohit-136 commented on Mar 4, 2019

    @rohit-136
    rohit-136
    on Mar 4, 2019

    @dcreager It still says "redundant linker flag specified for library stdc++".

  9. bors
    closed this as completedin #57018on Mar 20, 2019
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