Fix Access Violation when using lld & ThinLTO on windows-msvc #103353
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bjorn3
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r=me on the code changes, but I believe maybe r? @bjorn3. |
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I'm not a windows export, so I'm going to reassign it again. r? compiler |
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Great find, @wesleywiser! Could you try to add a regression test for this? |
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Thanks for the push to add a test @michaelwoerister! Added 🙂 |
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Users report an AV at runtime of the compiled binary when using lld and ThinLTO on windows-msvc. The AV occurs when accessing a static value which is defined in one crate but used in another. Based on the disassembly of the cross-crate use, it appears that the use is not correctly linked with the definition and is instead assigned a garbage pointer value. If we look at the symbol tables for each crates' obj file, we can see what is happening: *lib.obj*: ``` COFF SYMBOL TABLE ... 00E 00000000 SECT2 notype External | _ZN10reproducer7memrchr2FN17h612b61ca0e168901E ... ``` *bin.obj*: ``` COFF SYMBOL TABLE ... 010 00000000 UNDEF notype External | __imp__ZN10reproducer7memrchr2FN17h612b61ca0e168901E ... ``` The use of the symbol has the "import" style symbol name but the declaration doesn't generate any symbol with the same name. As a result, linking the files generates a warning from lld: > rust-lld: warning: bin.obj: locally defined symbol imported: reproducer::memrchr::FN::h612b61ca0e168901 (defined in lib.obj) [LNK4217] and the symbol reference remains undefined at runtime leading to the AV. To fix this, we just need to detect that we are performing ThinLTO (and thus, static linking) and omit the `dllimport` attribute on the extern item in LLVM IR.
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@michaelwoerister Now that #103610 has been merged, this should be ready to go. |
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Thanks, @wesleywiser! |
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…r=michaelwoerister Fix Access Violation when using lld & ThinLTO on windows-msvc Users report an AV at runtime of the compiled binary when using lld and ThinLTO on windows-msvc. The AV occurs when accessing a static value which is defined in one crate but used in another. Based on the disassembly of the cross-crate use, it appears that the use is not correctly linked with the definition and is instead assigned a garbage pointer value. If we look at the symbol tables for each crates' obj file, we can see what is happening: *lib.obj*: ``` COFF SYMBOL TABLE ... 00E 00000000 SECT2 notype External | _ZN10reproducer7memrchr2FN17h612b61ca0e168901E ... ``` *bin.obj*: ``` COFF SYMBOL TABLE ... 010 00000000 UNDEF notype External | __imp__ZN10reproducer7memrchr2FN17h612b61ca0e168901E ... ``` The use of the symbol has the "import" style symbol name but the declaration doesn't generate any symbol with the same name. As a result, linking the files generates a warning from lld: > rust-lld: warning: bin.obj: locally defined symbol imported: reproducer::memrchr::FN::h612b61ca0e168901 (defined in lib.obj) [LNK4217] and the symbol reference remains undefined at runtime leading to the AV. To fix this, we just need to detect that we are performing ThinLTO (and thus, static linking) and omit the `dllimport` attribute on the extern item in LLVM IR. Fixes rust-lang#81408
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…r=michaelwoerister Fix Access Violation when using lld & ThinLTO on windows-msvc Users report an AV at runtime of the compiled binary when using lld and ThinLTO on windows-msvc. The AV occurs when accessing a static value which is defined in one crate but used in another. Based on the disassembly of the cross-crate use, it appears that the use is not correctly linked with the definition and is instead assigned a garbage pointer value. If we look at the symbol tables for each crates' obj file, we can see what is happening: *lib.obj*: ``` COFF SYMBOL TABLE ... 00E 00000000 SECT2 notype External | _ZN10reproducer7memrchr2FN17h612b61ca0e168901E ... ``` *bin.obj*: ``` COFF SYMBOL TABLE ... 010 00000000 UNDEF notype External | __imp__ZN10reproducer7memrchr2FN17h612b61ca0e168901E ... ``` The use of the symbol has the "import" style symbol name but the declaration doesn't generate any symbol with the same name. As a result, linking the files generates a warning from lld: > rust-lld: warning: bin.obj: locally defined symbol imported: reproducer::memrchr::FN::h612b61ca0e168901 (defined in lib.obj) [LNK4217] and the symbol reference remains undefined at runtime leading to the AV. To fix this, we just need to detect that we are performing ThinLTO (and thus, static linking) and omit the `dllimport` attribute on the extern item in LLVM IR. Fixes rust-lang#81408
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…r=michaelwoerister Fix Access Violation when using lld & ThinLTO on windows-msvc Users report an AV at runtime of the compiled binary when using lld and ThinLTO on windows-msvc. The AV occurs when accessing a static value which is defined in one crate but used in another. Based on the disassembly of the cross-crate use, it appears that the use is not correctly linked with the definition and is instead assigned a garbage pointer value. If we look at the symbol tables for each crates' obj file, we can see what is happening: *lib.obj*: ``` COFF SYMBOL TABLE ... 00E 00000000 SECT2 notype External | _ZN10reproducer7memrchr2FN17h612b61ca0e168901E ... ``` *bin.obj*: ``` COFF SYMBOL TABLE ... 010 00000000 UNDEF notype External | __imp__ZN10reproducer7memrchr2FN17h612b61ca0e168901E ... ``` The use of the symbol has the "import" style symbol name but the declaration doesn't generate any symbol with the same name. As a result, linking the files generates a warning from lld: > rust-lld: warning: bin.obj: locally defined symbol imported: reproducer::memrchr::FN::h612b61ca0e168901 (defined in lib.obj) [LNK4217] and the symbol reference remains undefined at runtime leading to the AV. To fix this, we just need to detect that we are performing ThinLTO (and thus, static linking) and omit the `dllimport` attribute on the extern item in LLVM IR. Fixes rust-lang#81408
This was referenced Nov 8, 2022
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…earth Rollup of 7 pull requests Successful merges: - rust-lang#100508 (avoid making substs of type aliases late bound when used as fn args) - rust-lang#101381 (Test that target feature mix up with homogeneous floats is sound) - rust-lang#103353 (Fix Access Violation when using lld & ThinLTO on windows-msvc) - rust-lang#103521 (Avoid possible infinite loop when next_point reaching the end of file) - rust-lang#103559 (first move on a nested span_label) - rust-lang#103778 (Update several crates for improved support of the new targets) - rust-lang#103827 (Properly remap and check for substs compatibility in `confirm_impl_trait_in_trait_candidate`) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup
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Apply dllimport in ThinLTO for -Z dylib-lto This partially reverts rust-lang#103353 by properly applying `dllimport` if `-Z dylib-lto` is passed. That PR should probably fully be reverted as it looks quite sketchy. We don't know locally if the entire crate graph would be statically linked. This should hopefully be sufficient to make ThinLTO work for rustc on Windows. r? `@wesleywiser`
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Users report an AV at runtime of the compiled binary when using lld and ThinLTO on windows-msvc. The AV occurs when accessing a static value which is defined in one crate but used in another. Based on the disassembly of the cross-crate use, it appears that the use is not correctly linked with the definition and is instead assigned a garbage pointer value.
If we look at the symbol tables for each crates' obj file, we can see what is happening:
lib.obj:
bin.obj:
The use of the symbol has the "import" style symbol name but the declaration doesn't generate any symbol with the same name. As a result, linking the files generates a warning from lld:
and the symbol reference remains undefined at runtime leading to the AV.
To fix this, we just need to detect that we are performing ThinLTO (and thus, static linking) and omit the
dllimportattribute on the extern item in LLVM IR.Fixes #81408