LLVMRust symbols not defined when building with -Zcross-crate-inline-threshold=always

[saethlin]

I tried this code:

RUSTFLAGS_NOT_BOOTSTRAP=-Zcross-crate-inline-threshold=yes x build --stage 2 library

I expected to see this happen: build succeeds

Instead, this happened: huge linker error

  = note: /usr/bin/ld: /home/ben/rust-master/build/x86_64-unknown-linux-gnu/stage1-rustc/x86_64-unknown-linux-gnu/release/deps/rustc_main-7ded3dee8b4f0982.rustc_main.8884e0661a07df8b-cgu.00.rcgu.o: in function `rustc_codegen_llvm::debuginfo::metadata::extend_scope_to_file':
          /home/ben/rust-master/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs:1530:(.text._RINvMNtNtCs2lOlULwIAjb_17rustc_codegen_ssa3mir9debuginfoINtB3_10DebugScopeRNvNtNtCs4kfzHsID1rW_18rustc_codegen_llvm5llvm_3ffi8MetadataB1a_E25adjust_dbg_scope_for_spanNtNtB1h_7context9CodegenCxECsbIGDuTTUdex_10rustc_main+0x90): undefined reference to `LLVMRustDIBuilderCreateLexicalBlockFile'
          /usr/bin/ld: /home/ben/rust-master/build/x86_64-unknown-linux-gnu/stage1-rustc/x86_64-unknown-linux-gnu/release/deps/rustc_main-7ded3dee8b4f0982.rustc_main.8884e0661a07df8b-cgu.00.rcgu.o: in function `rustc_codegen_llvm::llvm_util::configure_llvm':
          /home/ben/rust-master/compiler/rustc_codegen_llvm/src/llvm_util.rs:53:(.text.unlikely._RINvMs0_NtNtNtCs7JBb18HWky5_3std10sys_common4once5futexNtB6_4Once4callNCINvMs0_NtNtBc_4sync4onceNtB1f_4Once9call_onceNCNvNtCs4kfzHsID1rW_18rustc_codegen_llvm9llvm_util4init0E0ECsbIGDuTTUdex_10rustc_main+0x1eb): undefined reference to `LLVMRustInstallFatalErrorHandler'
          /usr/bin/ld: /home/ben/rust-master/compiler/rustc_codegen_llvm/src/llvm_util.rs:58:(.text.unlikely._RINvMs0_NtNtNtCs7JBb18HWky5_3std10sys_common4once5futexNtB6_4Once4callNCINvMs0_NtNtBc_4sync4onceNtB1f_4Once9call_onceNCNvNtCs4kfzHsID1rW_18rustc_codegen_llvm9llvm_util4init0E0ECsbIGDuTTUdex_10rustc_main+0x22b): undefined reference to `LLVMRustDisableSystemDialogsOnCrash'
          /usr/bin/ld: /home/ben/rust-master/compiler/rustc_codegen_llvm/src/llvm_util.rs:124:(.text.unlikely._RINvMs0_NtNtNtCs7JBb18HWky5_3std10sys_common4once5futexNtB6_4Once4callNCINvMs0_NtNtBc_4sync4onceNtB1f_4Once9call_onceNCNvNtCs4kfzHsID1rW_18rustc_codegen_llvm9llvm_util4init0E0ECsbIGDuTTUdex_10rustc_main+0x616): undefined reference to `LLVMTimeTraceProfilerInitialize'
          /usr/bin/ld: /home/ben/rust-master/compiler/rustc_codegen_llvm/src/llvm_util.rs:129:(.text.unlikely._RINvMs0_NtNtNtCs7JBb18HWky5_3std10sys_common4once5futexNtB6_4Once4callNCINvMs0_NtNtBc_4sync4onceNtB1f_4Once9call_onceNCNvNtCs4kfzHsID1rW_18rustc_codegen_llvm9llvm_util4init0E0ECsbIGDuTTUdex_10rustc_main+0x820): undefined reference to `LLVMRustSetLLVMOptions'
          /usr/bin/ld: /home/ben/rust-master/build/x86_64-unknown-linux-gnu/stage1-rustc/x86_64-unknown-linux-gnu/release/deps/rustc_main-7ded3dee8b4f0982.rustc_main.8884e0661a07df8b-cgu.00.rcgu.o: in function `<rustc_codegen_llvm::context::CodegenCx as rustc_codegen_ssa::traits::consts::ConstMethods>::const_to_opt_uint::{closure#0}':
          /home/ben/rust-master/compiler/rustc_codegen_llvm/src/common.rs:223:(.text._RINvMs_NtNtCs2lOlULwIAjb_17rustc_codegen_ssa3mir5placeINtB5_8PlaceRefRNvNtNtCs4kfzHsID1rW_18rustc_codegen_llvm5llvm_3ffi5ValueE13project_indexNtNtB1c_7builder7BuilderECsbIGDuTTUdex_10rustc_main+0x63): undefined reference to `LLVMRustConstIntGetZExtValue'

... and on and on and on...

(it is entirely possible that the flag is broken, I haven't tried using it very many places yet)

[Noratrieb]

This flag causes all the rust code to be built downstream in rustc-main, I suspect the LLVMRust C++ symbols aren't being exported from librustc_driver.

[bjorn3]

Try adding #[link(name = "llvm-wrapper", kind = "static")] to

rust/compiler/rustc_codegen_llvm/src/llvm/ffi.rs

Line 825 in 19079cf

extern "C" {

and every other such extern "C" block that declares a function. This tells rustc that it needs to re-export these functions of the static library from the produced dylib.

[saethlin]

Progress! I now have a pile of

  = note: /usr/bin/ld: LLVMWriteBitcodeToFile: undefined version: 
          /usr/bin/ld: LLVMVoidTypeInContext: undefined version: 
          /usr/bin/ld: LLVMVectorType: undefined version: 
          /usr/bin/ld: LLVMValueAsMetadata: undefined version: 
          /usr/bin/ld: LLVMTypeOf: undefined version: 

[bjorn3]

Is LLVM statically or dynamically linked for you? If it is dynamically linked, I think the #[link(name = "llvm-wrapper", kind = "static")] should be removed for all functions that come from libLLVM.so rather than llvm-wrapper. That is all functions whose name doesn't start with LLVMRust.

[saethlin]

Dynamic. That got me down to just a few linker errors that now fit on my screen. I think I also need a link name on the normal LLVM extern block, but the name is something like "LLVM-17-rust-1.76.0-nightly".

[bjorn3]

For dynamic libraries it shouldn't matter. The build script already adds a -l with the library name and we don't need special handling for exporting symbols from dynamic libraries. What linker errors do you get now?

[saethlin]

Sorry about this

[tmiasko]

Functions starting with LLVMTimeTraceProfiler despite the name are defined in our llvm-wrapper, so should get the same treatment as those starting with LLVMRust.

[Noratrieb]

maybe they should be renamed instead 🙃

[saethlin]

Yeah, I can do that