From 642f34880532ff758be2fab9cae7dd6d0681ef2a Mon Sep 17 00:00:00 2001
From: bjorn3 <17426603+bjorn3@users.noreply.github.com>
Date: Sun, 5 Apr 2026 20:07:50 +0200
Subject: [PATCH] Fix linking two dylibs together when both depend on
 profiler_builtins

See the comment inside this commit for why.
---
 compiler/rustc_codegen_ssa/src/back/link.rs   |  4 ++-
 compiler/rustc_metadata/src/creader.rs        |  9 +++++-
 .../duplicate-profiler-builtins/dylib_a.rs    |  1 +
 .../duplicate-profiler-builtins/dylib_b.rs    |  1 +
 .../duplicate-profiler-builtins/main.rs       |  4 +++
 .../duplicate-profiler-builtins/rmake.rs      | 29 +++++++++++++++++++
 6 files changed, 46 insertions(+), 2 deletions(-)
 create mode 100644 tests/run-make/duplicate-profiler-builtins/dylib_a.rs
 create mode 100644 tests/run-make/duplicate-profiler-builtins/dylib_b.rs
 create mode 100644 tests/run-make/duplicate-profiler-builtins/main.rs
 create mode 100644 tests/run-make/duplicate-profiler-builtins/rmake.rs

diff --git a/compiler/rustc_codegen_ssa/src/back/link.rs b/compiler/rustc_codegen_ssa/src/back/link.rs
index 20e75f0fdfd2..cb22aac4e952 100644
--- a/compiler/rustc_codegen_ssa/src/back/link.rs
+++ b/compiler/rustc_codegen_ssa/src/back/link.rs
@@ -2972,9 +2972,11 @@ fn add_upstream_rust_crates(
         // We must always link crates `compiler_builtins` and `profiler_builtins` statically.
         // Even if they were already included into a dylib
         // (e.g. `libstd` when `-C prefer-dynamic` is used).
+        // HACK: `dependency_formats` can report `profiler_builtins` as `NotLinked`.
+        // See the comment in inject_profiler_runtime for why this is the case.
         let linkage = data[cnum];
         let link_static_crate = linkage == Linkage::Static
-            || linkage == Linkage::IncludedFromDylib
+            || (linkage == Linkage::IncludedFromDylib || linkage == Linkage::NotLinked)
                 && (crate_info.compiler_builtins == Some(cnum)
                     || crate_info.profiler_runtime == Some(cnum));
 
diff --git a/compiler/rustc_metadata/src/creader.rs b/compiler/rustc_metadata/src/creader.rs
index 3c8ea1a9f43d..f36485cf0338 100644
--- a/compiler/rustc_metadata/src/creader.rs
+++ b/compiler/rustc_metadata/src/creader.rs
@@ -1024,12 +1024,19 @@ fn inject_profiler_runtime(&mut self, tcx: TyCtxt<'_>) {
 
         info!("loading profiler");
 
+        // HACK: This uses conditional despite actually being unconditional to ensure that
+        // there is no error emitted when two dylibs independently depend on profiler_builtins.
+        // This is fine as profiler_builtins is always statically linked into the dylib just
+        // like compiler_builtins. Unlike compiler_builtins however there is no guaranteed
+        // common dylib that the duplicate crate check believes the crate to be included in.
+        // add_upstream_rust_crates has a corresponding check that forces profiler_builtins
+        // to be statically linked in even when marked as NotLinked.
         let name = Symbol::intern(&tcx.sess.opts.unstable_opts.profiler_runtime);
         let Some(cnum) = self.resolve_crate(
             tcx,
             name,
             DUMMY_SP,
-            CrateDepKind::Unconditional,
+            CrateDepKind::Conditional,
             CrateOrigin::Injected,
         ) else {
             return;
diff --git a/tests/run-make/duplicate-profiler-builtins/dylib_a.rs b/tests/run-make/duplicate-profiler-builtins/dylib_a.rs
new file mode 100644
index 000000000000..6833f3919994
--- /dev/null
+++ b/tests/run-make/duplicate-profiler-builtins/dylib_a.rs
@@ -0,0 +1 @@
+pub fn something() {}
diff --git a/tests/run-make/duplicate-profiler-builtins/dylib_b.rs b/tests/run-make/duplicate-profiler-builtins/dylib_b.rs
new file mode 100644
index 000000000000..b56f00f19d58
--- /dev/null
+++ b/tests/run-make/duplicate-profiler-builtins/dylib_b.rs
@@ -0,0 +1 @@
+pub fn something_else() {}
diff --git a/tests/run-make/duplicate-profiler-builtins/main.rs b/tests/run-make/duplicate-profiler-builtins/main.rs
new file mode 100644
index 000000000000..78677b37b5f7
--- /dev/null
+++ b/tests/run-make/duplicate-profiler-builtins/main.rs
@@ -0,0 +1,4 @@
+fn main() {
+    dylib_a::something();
+    dylib_b::something_else();
+}
diff --git a/tests/run-make/duplicate-profiler-builtins/rmake.rs b/tests/run-make/duplicate-profiler-builtins/rmake.rs
new file mode 100644
index 000000000000..2dc53d0ee59d
--- /dev/null
+++ b/tests/run-make/duplicate-profiler-builtins/rmake.rs
@@ -0,0 +1,29 @@
+// Checks that two dylibs compiled with code coverage enabled can be linked
+// together without getting an error about duplicate profiler_builtins.
+
+//@ needs-profiler-runtime
+
+use run_make_support::{dynamic_lib_name, rustc};
+
+fn main() {
+    rustc()
+        .crate_name("dylib_a")
+        .crate_type("dylib")
+        .arg("-Cinstrument-coverage")
+        .arg("-Cprefer-dynamic")
+        .input("dylib_a.rs")
+        .run();
+    rustc()
+        .crate_name("dylib_b")
+        .crate_type("dylib")
+        .arg("-Cinstrument-coverage")
+        .arg("-Cprefer-dynamic")
+        .input("dylib_b.rs")
+        .run();
+    rustc()
+        .crate_type("bin")
+        .extern_("dylib_a", dynamic_lib_name("dylib_a"))
+        .extern_("dylib_b", dynamic_lib_name("dylib_b"))
+        .input("main.rs")
+        .run();
+}