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Merged
merged 1 commit into from
Jul 1, 2021
Merged

Add suggestions for "undefined reference" link errors #86558

merged 1 commit into from
Jul 1, 2021

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syvb
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@syvb syvb commented Jun 22, 2021

This adds a suggestion for "undefined reference to ..." linking errors to install or specify the location to an external library. Since there is no defined error format for linkers, we just check if there was a failure and if that failure contains the string undefined reference to. This also makes it impossible to test this, since the output depends on the system linker. The output now looks like:

error: linking with `cc` failed: exit status: 1
  |
  = note: "cc" "-m64" "linking_failure.linking_failure.7rcbfp3g-cgu.0.rcgu.o" "linking_failure.linking_failure.7rcbfp3g-cgu.1.rcgu.o" "linking_failure.linking_failure.7rcbfp3g-cgu.2.rcgu.o" "linking_failure.linking_failure.7rcbfp3g-cgu.3.rcgu.o" "linking_failure.linking_failure.7rcbfp3g-cgu.4.rcgu.o" "linking_failure.linking_failure.7rcbfp3g-cgu.5.rcgu.o" "linking_failure.linking_failure.7rcbfp3g-cgu.6.rcgu.o" "linking_failure.linking_failure.7rcbfp3g-cgu.7.rcgu.o" "linking_failure.linking_failure.7rcbfp3g-cgu.8.rcgu.o" "linking_failure.53u64zklswtfazes.rcgu.o" "-Wl,--as-needed" "-L" "/home/smit/rustc-dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,--start-group" "-Wl,-Bstatic" "/home/smit/rustc-dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-01ce3ba5c629d02f.rlib" "/home/smit/rustc-dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libpanic_unwind-f1f2102409186354.rlib" "/home/smit/rustc-dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libminiz_oxide-1e8b6b56a999f838.rlib" "/home/smit/rustc-dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libadler-d0e93eb4e14f1d19.rlib" "/home/smit/rustc-dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libobject-1d7e39d75d082b43.rlib" "/home/smit/rustc-dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libaddr2line-ade42e945045b261.rlib" "/home/smit/rustc-dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libgimli-1a65064fccf4ebc1.rlib" "/home/smit/rustc-dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd_detect-4d699c310fdfe72d.rlib" "/home/smit/rustc-dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_demangle-1cafa68a696ec800.rlib" "/home/smit/rustc-dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libhashbrown-e9f1c8c4dab2f046.rlib" "/home/smit/rustc-dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_alloc-ecc1a743be25c7f7.rlib" "/home/smit/rustc-dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libunwind-e074031c4b66b6b6.rlib" "/home/smit/rustc-dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcfg_if-9aa6ed9f1d3bfd53.rlib" "/home/smit/rustc-dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/liblibc-7862bf96c2250ca0.rlib" "/home/smit/rustc-dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/liballoc-f02ce0dc7895b5fd.rlib" "/home/smit/rustc-dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_core-3af9c60917570521.rlib" "/home/smit/rustc-dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcore-ca16fc7bb3645684.rlib" "-Wl,--end-group" "/home/smit/rustc-dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcompiler_builtins-d8e1a5b7299604cc.rlib" "-Wl,-Bdynamic" "-lgcc_s" "-lutil" "-lrt" "-lpthread" "-lm" "-ldl" "-lc" "-Wl,--eh-frame-hdr" "-Wl,-znoexecstack" "-L" "/home/smit/rustc-dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-o" "linking_failure" "-Wl,--gc-sections" "-pie" "-Wl,-zrelro" "-Wl,-znow" "-nodefaultlibs"
  = note: /usr/bin/ld: linking_failure.linking_failure.7rcbfp3g-cgu.3.rcgu.o: in function `linking_failure::main':
          linking_failure.7rcbfp3g-cgu.3:(.text._ZN15linking_failure4main17h52b6e3052e444479E+0x3): undefined reference to `doesnt_exist_thiwthwfyl'
          clang: error: linker command failed with exit code 1 (use -v to see invocation)
          
  = help: some `extern` functions couldn't be found; you may need to install or specify the path to some dependencies
  = note: use the -L flag to specify the library lookup path
  = note: use the cargo:rustc-link-search directive to specify the library lookup path with Cargo (see https://doc.rust-lang.org/cargo/reference/build-scripts.html#rustc-link-search)

error: aborting due to previous error

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r? @petrochenkov

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@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jun 22, 2021
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petrochenkov commented Jun 30, 2021 •
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If you get to the undefined reference to errors it means that all the libraries passed with -l are already found, so adding more search paths with -L is unlikely to help.

The undefined reference to error likely means that the relevant -l option is forgotten entirely, so we need to recommend passing -l foo to rustc or cargo:rustc-link-lib=foo to cargo instead.

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This also makes it impossible to test this, since the output depends on the system linker.

You can add a test that will run only on Linux using the // only-linux directive, you can also suppress generation of the .stderr file with // dont-check-compiler-stderr if necessary.

@petrochenkov petrochenkov added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jun 30, 2021
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syvb commented Jun 30, 2021

@petrochenkov I've adjusted the error message to recommend -l instead.

The problem with lacking tests goes beyond the output changing between systems -- it's possible that the user has a linker that uses a different error format on their system. While the current version of GCC ld (and pretty much all Unix linkers) output undefined reference to when that is in the case, AFAIK there is no standard that requires them to use that exact phrase. So it is possible that in the future the "was there a undefined reference linking error" heuristic will be wrong.

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@Smittyvb

So it is possible that in the future the "was there a undefined reference linking error" heuristic will be wrong.

Ok, looks like we don't need to consider arbitrary future, even LLD produces a different message now:

  = note: lld-link: error: undefined symbol: foo

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r=me after updating the wording and squashing commits.

@syvb syvb force-pushed the link-error-sugg branch from 11e0e96 to ce63d55 Compare June 30, 2021 22:08
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@bors r+ rollup

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bors commented Jun 30, 2021

📌 Commit ce63d55 has been approved by petrochenkov

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jun 30, 2021
@GuillaumeGomez GuillaumeGomez mentioned this pull request Jul 1, 2021
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bors added a commit to rust-lang-ci/rust that referenced this pull request Jul 1, 2021
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Auto merge of rust-lang#86774 - GuillaumeGomez:rollup-rkcgvph, r=Guil…
3cb1c11 
…laumeGomez

Rollup of 6 pull requests

Successful merges:

 - rust-lang#86558 (Add suggestions for "undefined reference" link errors)
 - rust-lang#86616 (rustc_span: Explicitly handle crates that differ from package names)
 - rust-lang#86652 (Add support for leaf function frame pointer elimination)
 - rust-lang#86666 (Fix misleading "impl Trait" error)
 - rust-lang#86762 (mailmap: Add my work email address)
 - rust-lang#86773 (Enable the tests developed with rust-lang#86594)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit 75f2263 into rust-lang:master Jul 1, 2021
@rustbot rustbot added this to the 1.55.0 milestone Jul 1, 2021
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