Check to ensure we're running against the correct LLVM version

[jnkel]

The recent LLVM version bump exposed several cases of mishandling LLVM versions, both in-tree and downstream (#161335, #161377, #161572, #162013, https://rust-lang.zulipchat.com/#narrow/channel/122651-general/topic/opt-dist.20pipeline.20failure.20in.20MSYS2.20CI.20when.20compiling.2E.2E.2E/with/619077952).

If the compiler is run against an incompatible LLVM version, the most common failure mode is a segfault within LLVM, often when looking up target information. This is not obvious to debug, so this PR adds an LLVM version check before initializing LLVM so that we can produce a clearer error.

The second commit in this PR performs a dladdr lookup to print the path to the LLVM we're using. We already have code to do this for finding the sysroot, which I repurposed. However, I don't mind reverting this if it's too complex/risky.

I would appreciate if someone with permissions could trigger a try build on AIX, Windows, and WASI as the second commit touches platform-specific code that I can't test locally.

Before:

error: rustc interrupted by SIGSEGV, printing backtrace
0   librustc_driver-18049a207bb38ba8.dy 0x000000010e09e9b8 _RNvNtCsfNrGi27GPxl_17rustc_driver_impl14signal_handler17print_stack_trace + 140
1   libsystem_platform.dylib            0x0000000184c7d744 _sigtramp + 56
2   libLLVM.dylib                       0x000000011a9e22e0 _ZNK4llvm15MCSubtargetInfo13checkFeaturesENS_9StringRefE + 40
3   librustc_driver-18049a207bb38ba8.dy 0x000000010e44c798 LLVMRustHasFeature + 104
4   librustc_driver-18049a207bb38ba8.dy 0x000000010e3c4e34 _RINvXs0_NtNtNtCsk8HLZXaYIk4_4core4iter8adapters3mapINtB6_3MapINtNtB8_7flatten7FlatMapINtNtB8_6filter6FilterINtNtNtBc_5slice4iter4IterTReNtNtCs79s86CIooN0_12rustc_target15target_features9StabilityRSB28_EENCINvNtCses5MBT5CPFU_17rustc_codegen_ssa15target_features24internal_target_featuresKj2_NCNvNtCsgXm2bqwPj4W_18rustc_codegen_llvm9llvm_util13target_config0NCB4G_s_0E0EIBO_INtNtNtNtCs99cPMl0y5Ob_3std11collections4hash3set8IntoIterB28_ENCNCB3h_s_00ENCB3h_s_0ENCINvXs8_NtCsdLs5ZkLaCXa_9hashbrown3setINtB7v_7HashSetNtNtCsSGoTcZpb2F_10rustc_span6symbol6SymbolNtCs5ZGGmiYplBm_10rustc_hash13FxBuildHasherEINtNtNtBa_6traits7collect6ExtendB8e_E6extendBX_E0ENtNtB9I_8iterator8Iterator4folduNCINvNvBar_8for_each4callTB8e_uENCINvXs1i_NtB7x_3mapINtBbD_7HashMapB8e_uB8V_EIB9E_Bbm_E6extendBN_E0E0EB4K_ + 880
5   librustc_driver-18049a207bb38ba8.dy 0x000000010e2ad884 _RINvXs1i_NtCsdLs5ZkLaCXa_9hashbrown3mapINtB7_7HashMapNtNtCsSGoTcZpb2F_10rustc_span6symbol6SymboluNtCs5ZGGmiYplBm_10rustc_hash13FxBuildHasherEINtNtNtNtCsk8HLZXaYIk4_4core4iter6traits7collect6ExtendTBP_uEE6extendINtNtNtB2m_8adapters3map3MapINtNtB3r_7flatten7FlatMapINtNtB3r_6filter6FilterINtNtNtB2o_5slice4iter4IterTReNtNtCs79s86CIooN0_12rustc_target15target_features9StabilityRSB52_EENCINvNtCses5MBT5CPFU_17rustc_codegen_ssa15target_features24internal_target_featuresKj2_NCNvNtCsgXm2bqwPj4W_18rustc_codegen_llvm9llvm_util13target_config0NCB7A_s_0E0EIB3n_INtNtNtNtCs99cPMl0y5Ob_3std11collections4hash3set8IntoIterB52_ENCNCB6b_s_00ENCB6b_s_0ENCINvXs8_NtB9_3setINtBaq_7HashSetBP_B1x_EIB2g_BP_E6extendB3O_E0EEB7E_ + 344
6   librustc_driver-18049a207bb38ba8.dy 0x000000010e2b1ec4 _RINvXs8_NtCsdLs5ZkLaCXa_9hashbrown3setINtB6_7HashSetNtNtCsSGoTcZpb2F_10rustc_span6symbol6SymbolNtCs5ZGGmiYplBm_10rustc_hash13FxBuildHasherEINtNtNtNtCsk8HLZXaYIk4_4core4iter6traits7collect6ExtendBO_E6extendINtNtNtB2k_8adapters7flatten7FlatMapINtNtB3m_6filter6FilterINtNtNtB2m_5slice4iter4IterTReNtNtCs79s86CIooN0_12rustc_target15target_features9StabilityRSB4G_EENCINvNtCses5MBT5CPFU_17rustc_codegen_ssa15target_features24internal_target_featuresKj2_NCNvNtCsgXm2bqwPj4W_18rustc_codegen_llvm9llvm_util13target_config0NCB7e_s_0E0EINtNtB3m_3map3MapINtNtNtNtCs99cPMl0y5Ob_3std11collections4hash3set8IntoIterB4G_ENCNCB5P_s_00ENCB5P_s_0EEB7i_ + 68
7   librustc_driver-18049a207bb38ba8.dy 0x000000010e2bfa90 _RINvNtCses5MBT5CPFU_17rustc_codegen_ssa15target_features24internal_target_featuresKj2_NCNvNtCsgXm2bqwPj4W_18rustc_codegen_llvm9llvm_util13target_config0NCB1o_s_0EB1s_ + 148
8   librustc_driver-18049a207bb38ba8.dy 0x000000010e2fb918 _RNvNtCsgXm2bqwPj4W_18rustc_codegen_llvm9llvm_util13target_config + 68
9   librustc_driver-18049a207bb38ba8.dy 0x000000010e292fb0 _RNvNtCs6x0lOIkloew_15rustc_interface4util17add_configuration + 48
10  librustc_driver-18049a207bb38ba8.dy 0x000000010e06b204 _RINvMs_Csfkr8sXZt4uY_10scoped_tlsINtB5_9ScopedKeyNtCsSGoTcZpb2F_10rustc_span14SessionGlobalsE3setNCNCNCINvNtCs6x0lOIkloew_15rustc_interface4util26run_in_thread_with_globalsNCINvB1G_31run_in_thread_pool_with_globalsNCINvNtB1I_9interface12run_compileruNCNvCsfNrGi27GPxl_17rustc_driver_impl12run_compiler0Es0_0uE0uE000uEB44_ + 1112
11  librustc_driver-18049a207bb38ba8.dy 0x000000010e090914 _RINvCsSGoTcZpb2F_10rustc_span27create_session_globals_thenuNCNCNCINvNtCs6x0lOIkloew_15rustc_interface4util26run_in_thread_with_globalsNCINvB14_31run_in_thread_pool_with_globalsNCINvNtB16_9interface12run_compileruNCNvCsfNrGi27GPxl_17rustc_driver_impl12run_compiler0Es0_0uE0uE000EB3s_ + 168
12  librustc_driver-18049a207bb38ba8.dy 0x000000010e07823c _RINvNtNtCs99cPMl0y5Ob_3std3sys9backtrace28___rust_begin_short_backtraceNCNCINvNtCs6x0lOIkloew_15rustc_interface4util26run_in_thread_with_globalsNCINvB1e_31run_in_thread_pool_with_globalsNCINvNtB1g_9interface12run_compileruNCNvCsfNrGi27GPxl_17rustc_driver_impl12run_compiler0Es0_0uE0uE00uEB3C_ + 112
13  librustc_driver-18049a207bb38ba8.dy 0x000000010e04efa4 _RNSNvYNCINvNtNtCs99cPMl0y5Ob_3std6thread9lifecycle15spawn_uncheckedNCNCINvNtCs6x0lOIkloew_15rustc_interface4util26run_in_thread_with_globalsNCINvB1a_31run_in_thread_pool_with_globalsNCINvNtB1c_9interface12run_compileruNCNvCsfNrGi27GPxl_17rustc_driver_impl12run_compiler0Es0_0uE0uE00uEs_0INtNtNtCsk8HLZXaYIk4_4core3ops8function6FnOnceuE9call_once6vtableB3y_ + 208
14  librustc_driver-18049a207bb38ba8.dy 0x0000000111697118 _RNvNvMs0_NtNtNtCs99cPMl0y5Ob_3std3sys6thread4unixNtB7_6Thread3new12thread_start + 392
15  libsystem_pthread.dylib             0x0000000184c73c58 _pthread_start + 136
16  libsystem_pthread.dylib             0x0000000184c6ec1c thread_start + 8

note: we would appreciate a report at https://github.com/rust-lang/rust
help: you can increase rustc's stack size by setting RUST_MIN_STACK=33554432

After:

thread 'rustc' (3568488) panicked at compiler/rustc_codegen_llvm/src/llvm_util.rs:59:13:
LLVM version mismatch: this compiler was built for LLVM 23, but LLVM 22.1.8 was found at /Users/keljonathan/code/rust/build/aarch64-apple-darwin/stage0/lib/libLLVM.dylib
stack backtrace:
   0: __rustc::rust_begin_unwind
             at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/panicking.rs:679:5
   1: core::panicking::panic_fmt
             at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/core/src/panicking.rs:80:14
   2: configure_llvm
             at ./compiler/rustc_codegen_llvm/src/llvm_util.rs:59:13
   3: {closure#0}
             at ./compiler/rustc_codegen_llvm/src/llvm_util.rs:35:13
   4: {closure#0}<rustc_codegen_llvm::llvm_util::init::{closure_env#0}>
             at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/sync/once.rs:166:41
   5: <std::sys::sync::once::queue::Once>::call
             at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/sys/sync/once/queue.rs:225:21
   6: call_once<rustc_codegen_llvm::llvm_util::init::{closure_env#0}>
             at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/sync/once.rs:166:20
   7: init
             at ./compiler/rustc_codegen_llvm/src/llvm_util.rs:34:14
   8: init
             at ./compiler/rustc_codegen_llvm/src/lib.rs:223:9
   9: {closure#2}<(), rustc_driver_impl::run_compiler::{closure_env#0}>
             at ./compiler/rustc_interface/src/interface.rs:440:29
  10: {closure#0}<rustc_interface::interface::run_compiler::{closure_env#2}<(), rustc_driver_impl::run_compiler::{closure_env#0}>, ()>
             at ./compiler/rustc_interface/src/util.rs:223:17
  11: {closure#0}<rustc_interface::util::run_in_thread_pool_with_globals::{closure_env#0}<rustc_interface::interface::run_compiler::{closure_env#2}<(), rustc_driver_impl::run_compiler::{closure_env#0}>, ()>, ()>
             at ./compiler/rustc_interface/src/util.rs:180:24
  12: set<rustc_span::SessionGlobals, rustc_interface::util::run_in_thread_with_globals::{closure#0}::{closure#0}::{closure_env#0}<rustc_interface::util::run_in_thread_pool_with_globals::{closure_env#0}<rustc_interface::interface::run_compiler::{closure_env#2}<(), rustc_driver_impl::run_compiler::{closure_env#0}>, ()>, ()>, ()>
             at /Users/keljonathan/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/scoped-tls-1.0.1/src/lib.rs:137:9
  13: create_session_globals_then<(), rustc_interface::util::run_in_thread_with_globals::{closure#0}::{closure#0}::{closure_env#0}<rustc_interface::util::run_in_thread_pool_with_globals::{closure_env#0}<rustc_interface::interface::run_compiler::{closure_env#2}<(), rustc_driver_impl::run_compiler::{closure_env#0}>, ()>, ()>>
             at ./compiler/rustc_span/src/lib.rs:156:21
  14: {closure#0}<rustc_interface::util::run_in_thread_pool_with_globals::{closure_env#0}<rustc_interface::interface::run_compiler::{closure_env#2}<(), rustc_driver_impl::run_compiler::{closure_env#0}>, ()>, ()>
             at ./compiler/rustc_interface/src/util.rs:176:17
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

error: the compiler unexpectedly panicked. This is a bug

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: please make sure that you have updated to the latest nightly

note: please attach the file at `/Users/keljonathan/code/rust/rustc-ice-2026-08-25T22_23_11-1423.txt` to your bug report

note: rustc 1.100.0-dev running on aarch64-apple-darwin

note: compiler flags: -C rpath -C debuginfo=0 -Z unstable-options

query stack during panic:
end of query stack

[rustbot]

r? @nnethercote

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[Zalathar]

AIX seems to be tier 3 so I don't know that we have any tests for it.

Anyhow, here's an assortment of try jobs:

@bors try jobs=test-various,dist-various-1,dist-various-2,x86_64-msvc-1,x86_64-msvc-2,aarch64-apple-1,aarch64-apple-2

[rust-bors]

☀️ Try build successful (CI)
Build commit: 6df9663 (6df966363bf7966dc66a6a14597ed4de2ec8492c)
Base parent: 0f33d09 (0f33d0912709e847199218ebab88e2311872f364)

[saethlin]

@bors r+

I'm not the foremost expert on these components but I think this looks pretty good and we keep getting issues filed about segfaults that this would clarify.

[rust-bors]

📌 Commit 5841e10 has been approved by saethlin

It is now in the queue for this repository.