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ThinLTO breaks MSVC _imp_ symbols #45347

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alexcrichton opened this issue Oct 17, 2017 · 1 comment · Fixed by #45348
Closed

ThinLTO breaks MSVC _imp_ symbols #45347

alexcrichton opened this issue Oct 17, 2017 · 1 comment · Fixed by #45348
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A-codegen Area: Code generation O-windows-msvc Toolchain: MSVC, Operating system: Windows

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@alexcrichton
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I believe this is a minimization of this reported issue:

$ cat bar.rs
pub static A: u32 = 43;

pub mod a {
    pub static A: u32 = 43;
}
$ cat foo.rs
extern crate bar;

fn main() {
    println!("{}", bar::A);
}
$ rustc +nightly bar.rs -C prefer-dynamic -Z thinlto -C codegen-units=1000 --crate-type dylib,rlib -O
$ rustc +nightly foo.rs -L . -Z thinlto -Z print-link-args
error: linking with `link.exe` failed: exit code: 1120
  |
  = note: "C:\\Program Files (x86)\\Microsoft Visual Studio\\2017\\Community\\VC\\Tools\\MSVC\\14.10.25017\\bin\\HostX64\\x64\\link.exe" "/NOLOGO" "/NXCOMPAT" "/LIBPATH:C:\\Users\\alex\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib" "foo.foo0-8cd878b7c8d78940dfe6697baf5b88ec-exe.rs.rust-cgu.o" "foo.foo1-8cd878b7c8d78940dfe6697baf5b88ec-exe.rs.rust-cgu.o" "/OUT:foo.exe" "foo.crate.allocator.rust-cgu.o" "/OPT:REF,NOICF" "/DEBUG" "/NATVIS:C:\\Users\\alex\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\etc\\liballoc.natvis" "/NATVIS:C:\\Users\\alex\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\etc\\libcore.natvis" "/LIBPATH:." "/LIBPATH:C:\\Users\\alex\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib" "C:\\msys64\\code\\rustfmt\\libbar.rlib" "C:\\Users\\alex\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libstd-2c973d468aa52913.rlib" "C:\\Users\\alex\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libpanic_unwind-10dcb2bb73715353.rlib" "C:\\Users\\alex\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libunwind-eac2a22c7ef68dc5.rlib" "C:\\Users\\alex\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\liblibc-6232007b55cca9f2.rlib" "C:\\Users\\alex\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\liballoc_system-968b8d6a8dcae5d4.rlib" "C:\\Users\\alex\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\liballoc-bba7ff6cfd33a952.rlib" "C:\\Users\\alex\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libstd_unicode-6001d57e726caccd.rlib" "C:\\Users\\alex\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\librand-d98f06e2ac3721a9.rlib" "C:\\Users\\alex\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libcore-15daeee4c05dda88.rlib" "C:\\Users\\alex\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libcompiler_builtins-b02255a955089c1d.rlib" "advapi32.lib" "ws2_32.lib" "userenv.lib" "shell32.lib" "msvcrt.lib"
  = note: foo.foo0-8cd878b7c8d78940dfe6697baf5b88ec-exe.rs.rust-cgu.o : error LNK2019: unresolved external symbol __imp__ZN3bar1A17h8c3f932ba2a49b51E referenced in function _ZN3foo4main17hd45fff29dc617b3fE.llvm.C758FA11
          foo.exe : fatal error LNK1120: 1 unresolved externals


error: aborting due to previous error
@alexcrichton alexcrichton added A-codegen Area: Code generation O-windows-msvc Toolchain: MSVC, Operating system: Windows labels Oct 17, 2017
@alexcrichton alexcrichton mentioned this issue Oct 17, 2017
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@alexcrichton
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I've got a fix for this in the works.

@alexcrichton alexcrichton mentioned this issue Oct 18, 2017
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alexcrichton added a commit to alexcrichton/rust that referenced this issue Oct 18, 2017
@alexcrichton
rustc: Add _imp_ symbols later in compilation
3541ffb 
On MSVC targets rustc will add symbols prefixed with `_imp_` to LLVM modules to
"emulate" dllexported statics as that workaround is still in place after rust-lang#27438
hasn't been solved otherwise. These statics, however, were getting gc'd by
ThinLTO accidentally which later would cause linking failures.

This commit updates the location we add such symbols to happen just before
codegen to ensure that (a) they're not eliminated by the optimizer and (b) the
optimizer doesn't even worry about them.

Closes rust-lang#45347
bors added a commit that referenced this issue Oct 20, 2017
@bors
Auto merge of #45348 - alexcrichton:thinlto-timp, r=michaelwoerister
6511b4f 
rustc: Add `_imp_` symbols later in compilation

On MSVC targets rustc will add symbols prefixed with `_imp_` to LLVM modules to
"emulate" dllexported statics as that workaround is still in place after #27438
hasn't been solved otherwise. These statics, however, were getting gc'd by
ThinLTO accidentally which later would cause linking failures.

This commit updates the location we add such symbols to happen just before
codegen to ensure that (a) they're not eliminated by the optimizer and (b) the
optimizer doesn't even worry about them.

Closes #45347
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rustc: Add _imp_ symbols later in compilation alexcrichton/rust
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