llvm: change data layout bug to an error and make it trigger more

compiler/rustc_codegen_llvm/messages.ftl

@@ -39,6 +39,9 @@ codegen_llvm_lto_dylib = lto cannot be used for `dylib` crate type without `-Zdy
 
 codegen_llvm_lto_proc_macro = lto cannot be used for `proc-macro` crate type without `-Zdylib-lto`
 
+codegen_llvm_mismatch_data_layout =
+    data-layout for target `{$rustc_target}`, `{$rustc_layout}`, differs from LLVM target's `{$llvm_target}` default layout, `{$llvm_layout}`
+
 codegen_llvm_missing_features =
     add the missing features in a `target_feature` attribute
 

compiler/rustc_codegen_llvm/src/context.rs

@@ -34,6 +34,7 @@ use rustc_target::spec::{HasTargetSpec, RelocModel, Target, TlsModel};
 use smallvec::SmallVec;
 
 use libc::c_uint;
+use std::borrow::Borrow;
 use std::cell::{Cell, RefCell};
 use std::ffi::CStr;
 use std::str;
@@ -147,42 +148,21 @@ pub unsafe fn create_module<'ll>(
     }
 
     // Ensure the data-layout values hardcoded remain the defaults.
-    if sess.target.is_builtin {
-        // tm is disposed by its drop impl
+    {
         let tm = crate::back::write::create_informational_target_machine(tcx.sess);
         llvm::LLVMRustSetDataLayoutFromTargetMachine(llmod, &tm);
 
         let llvm_data_layout = llvm::LLVMGetDataLayoutStr(llmod);
         let llvm_data_layout = str::from_utf8(CStr::from_ptr(llvm_data_layout).to_bytes())
             .expect("got a non-UTF8 data-layout from LLVM");
 
-        // Unfortunately LLVM target specs change over time, and right now we
-        // don't have proper support to work with any more than one
-        // `data_layout` than the one that is in the rust-lang/rust repo. If
-        // this compiler is configured against a custom LLVM, we may have a
-        // differing data layout, even though we should update our own to use
-        // that one.
-        //
-        // As an interim hack, if CFG_LLVM_ROOT is not an empty string then we
-        // disable this check entirely as we may be configured with something
-        // that has a different target layout.
-        //
-        // Unsure if this will actually cause breakage when rustc is configured
-        // as such.
-        //
-        // FIXME(#34960)
-        let cfg_llvm_root = option_env!("CFG_LLVM_ROOT").unwrap_or("");
-        let custom_llvm_used = !cfg_llvm_root.trim().is_empty();
-
-        if !custom_llvm_used && target_data_layout != llvm_data_layout {
-            bug!(
-                "data-layout for target `{rustc_target}`, `{rustc_layout}`, \
-                  differs from LLVM target's `{llvm_target}` default layout, `{llvm_layout}`",
-                rustc_target = sess.opts.target_triple,
-                rustc_layout = target_data_layout,
-                llvm_target = sess.target.llvm_target,
-                llvm_layout = llvm_data_layout
-            );
+        if target_data_layout != llvm_data_layout {
+            tcx.dcx().emit_err(crate::errors::MismatchedDataLayout {
+                rustc_target: sess.opts.target_triple.to_string().as_str(),
+                rustc_layout: target_data_layout.as_str(),
+                llvm_target: sess.target.llvm_target.borrow(),
+                llvm_layout: llvm_data_layout,
+            });
         }
     }
 

compiler/rustc_codegen_llvm/src/errors.rs

@@ -244,3 +244,12 @@ pub(crate) struct CopyBitcode {
 pub struct UnknownCompression {
     pub algorithm: &'static str,
 }
+
+#[derive(Diagnostic)]
+#[diag(codegen_llvm_mismatch_data_layout)]
+pub struct MismatchedDataLayout<'a> {
+    pub rustc_target: &'a str,
+    pub rustc_layout: &'a str,
+    pub llvm_target: &'a str,
+    pub llvm_layout: &'a str,
+}

src/bootstrap/src/core/build_steps/compile.rs

@@ -1103,16 +1103,11 @@ pub fn rustc_cargo_env(
 /// Pass down configuration from the LLVM build into the build of
 /// rustc_llvm and rustc_codegen_llvm.
 fn rustc_llvm_env(builder: &Builder<'_>, cargo: &mut Cargo, target: TargetSelection) {
-    let target_config = builder.config.target_config.get(&target);
-
     if builder.is_rust_llvm(target) {
         cargo.env("LLVM_RUSTLLVM", "1");
     }
     let llvm::LlvmResult { llvm_config, .. } = builder.ensure(llvm::Llvm { target });
     cargo.env("LLVM_CONFIG", &llvm_config);
-    if let Some(s) = target_config.and_then(|c| c.llvm_config.as_ref()) {
-        cargo.env("CFG_LLVM_ROOT", s);
-    }
 
     // Some LLVM linker flags (-L and -l) may be needed to link `rustc_llvm`. Its build script
     // expects these to be passed via the `LLVM_LINKER_FLAGS` env variable, separated by

src/tools/tidy/src/ui_tests.rs

@@ -24,9 +24,10 @@ const EXPECTED_TEST_FILE_EXTENSIONS: &[&str] = &[
 
 const EXTENSION_EXCEPTION_PATHS: &[&str] = &[
     "tests/ui/asm/named-asm-labels.s", // loading an external asm file to test named labels lint
-    "tests/ui/check-cfg/my-awesome-platform.json", // testing custom targets with cfgs
-    "tests/ui/commandline-argfile-badutf8.args", // passing args via a file
-    "tests/ui/commandline-argfile.args", // passing args via a file
+    "tests/ui/codegen/mismatched-data-layout.json", // testing mismatched data layout w/ custom targets
+    "tests/ui/check-cfg/my-awesome-platform.json",  // testing custom targets with cfgs
+    "tests/ui/commandline-argfile-badutf8.args",    // passing args via a file
+    "tests/ui/commandline-argfile.args",            // passing args via a file
     "tests/ui/crate-loading/auxiliary/libfoo.rlib", // testing loading a manually created rlib
     "tests/ui/include-macros/data.bin", // testing including data with the include macros
     "tests/ui/include-macros/file.txt", // testing including data with the include macros

tests/run-make/target-specs/Makefile

@@ -9,4 +9,4 @@ all:
 	$(RUSTC) -Z unstable-options --target=my-awesome-platform.json --print target-spec-json > $(TMPDIR)/test-platform.json && $(RUSTC) -Z unstable-options --target=$(TMPDIR)/test-platform.json --print target-spec-json | diff -q $(TMPDIR)/test-platform.json -
 	$(RUSTC) foo.rs --target=definitely-not-builtin-target 2>&1 | $(CGREP) 'may not set is_builtin'
 	$(RUSTC) foo.rs --target=endianness-mismatch 2>&1 | $(CGREP) '"data-layout" claims architecture is little-endian'
-	$(RUSTC) foo.rs --target=mismatching-data-layout --crate-type=lib
+	$(RUSTC) foo.rs --target=mismatching-data-layout --crate-type=lib 2>&1 | $(CGREP) 'data-layout for target'

tests/ui/codegen/mismatched-data-layout.json

@@ -0,0 +1,13 @@
+{
+    "llvm-target": "x86_64-unknown-none-gnu",
+    "data-layout": "e-m:e-i64:64-f80:128-n8:16:32:64-S128",
+    "arch": "x86_64",
+    "target-endian": "little",
+    "target-pointer-width": "64",
+    "target-c-int-width": "32",
+    "os": "unknown",
+    "linker-flavor": "ld.lld",
+    "linker": "rust-lld",
+    "executables": true
+}
+

tests/ui/codegen/mismatched-data-layouts.rs

@@ -0,0 +1,14 @@
+// This test checks that data layout mismatches emit an error.
+//
+// build-fail
+// needs-llvm-components: x86
+// compile-flags: --crate-type=lib --target={{src-base}}/codegen/mismatched-data-layout.json -Z unstable-options
+// error-pattern: differs from LLVM target's
+// normalize-stderr-test: "`, `[A-Za-z0-9-:]*`" -> "`, `normalized data layout`"
+// normalize-stderr-test: "layout, `[A-Za-z0-9-:]*`" -> "layout, `normalized data layout`"
+
+#![feature(lang_items, no_core, auto_traits)]
+#![no_core]
+
+#[lang = "sized"]
+trait Sized {}

tests/ui/codegen/mismatched-data-layouts.stderr

@@ -0,0 +1,4 @@
+error: data-layout for target `mismatched-data-layout-7814813422914914169`, `normalized data layout`, differs from LLVM target's `x86_64-unknown-none-gnu` default layout, `normalized data layout`
+
+error: aborting due to 1 previous error
+