[Driver] Search for compiler-rt libraries in sysroot/lib if not found in the resource directory

[Sunday111]

This patch improves support for embedded Linux toolchains with multiple sysroots, each containing different built-in libraries. If compiler-rt libraries are not found in the resource directory, the Clang driver will fallback to searching in the sysroot/lib directory.

This change preserves the standard behavior for regular Linux toolchains while allowing greater flexibility in toolchains with multiple sysroots.

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[llvmbot]

@llvm/pr-subscribers-clang

@llvm/pr-subscribers-clang-driver

Author: Kostiantyn Lazukin (Sunday111)

Changes

This patch improves support for embedded Linux toolchains with multiple sysroots, each containing different built-in libraries. If compiler-rt libraries are not found in the resource directory, the Clang driver will fallback to searching in the sysroot/lib directory.

This change preserves the standard behavior for regular Linux toolchains while allowing greater flexibility in toolchains with multiple sysroots.

---

Full diff: https://github.com/llvm/llvm-project/pull/132443.diff

9 Files Affected:

• (modified) clang/lib/Driver/ToolChains/Linux.cpp (+2)
• (added) clang/test/Driver/Inputs/musl_sysroot_with_builtins/lib/Scrt1.o ()
• (added) clang/test/Driver/Inputs/musl_sysroot_with_builtins/lib/clang_rt.crtbegin.o ()
• (added) clang/test/Driver/Inputs/musl_sysroot_with_builtins/lib/clang_rt.crtend.o ()
• (added) clang/test/Driver/Inputs/musl_sysroot_with_builtins/lib/crti.o ()
• (added) clang/test/Driver/Inputs/musl_sysroot_with_builtins/lib/crtn.o ()
• (added) clang/test/Driver/Inputs/musl_sysroot_with_builtins/lib/libclang_rt.builtins.a ()
• (added) clang/test/Driver/Inputs/resource_dir_empty/keep ()
• (added) clang/test/Driver/linux-musl-library-search.cpp (+14)

diff --git a/clang/lib/Driver/ToolChains/Linux.cpp b/clang/lib/Driver/ToolChains/Linux.cpp
index 1e9bd3de75f04..1bd8daafa8091 100644
--- a/clang/lib/Driver/ToolChains/Linux.cpp
+++ b/clang/lib/Driver/ToolChains/Linux.cpp
@@ -354,6 +354,8 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
 
   addPathIfExists(D, concat(SysRoot, "/lib"), Paths);
   addPathIfExists(D, concat(SysRoot, "/usr/lib"), Paths);
+
+  addPathIfExists(D, concat(SysRoot, "/lib"), getLibraryPaths());
 }
 
 ToolChain::RuntimeLibType Linux::GetDefaultRuntimeLibType() const {
diff --git a/clang/test/Driver/Inputs/musl_sysroot_with_builtins/lib/Scrt1.o b/clang/test/Driver/Inputs/musl_sysroot_with_builtins/lib/Scrt1.o
new file mode 100644
index 0000000000000..e69de29bb2d1d
diff --git a/clang/test/Driver/Inputs/musl_sysroot_with_builtins/lib/clang_rt.crtbegin.o b/clang/test/Driver/Inputs/musl_sysroot_with_builtins/lib/clang_rt.crtbegin.o
new file mode 100644
index 0000000000000..e69de29bb2d1d
diff --git a/clang/test/Driver/Inputs/musl_sysroot_with_builtins/lib/clang_rt.crtend.o b/clang/test/Driver/Inputs/musl_sysroot_with_builtins/lib/clang_rt.crtend.o
new file mode 100644
index 0000000000000..e69de29bb2d1d
diff --git a/clang/test/Driver/Inputs/musl_sysroot_with_builtins/lib/crti.o b/clang/test/Driver/Inputs/musl_sysroot_with_builtins/lib/crti.o
new file mode 100644
index 0000000000000..e69de29bb2d1d
diff --git a/clang/test/Driver/Inputs/musl_sysroot_with_builtins/lib/crtn.o b/clang/test/Driver/Inputs/musl_sysroot_with_builtins/lib/crtn.o
new file mode 100644
index 0000000000000..e69de29bb2d1d
diff --git a/clang/test/Driver/Inputs/musl_sysroot_with_builtins/lib/libclang_rt.builtins.a b/clang/test/Driver/Inputs/musl_sysroot_with_builtins/lib/libclang_rt.builtins.a
new file mode 100644
index 0000000000000..e69de29bb2d1d
diff --git a/clang/test/Driver/Inputs/resource_dir_empty/keep b/clang/test/Driver/Inputs/resource_dir_empty/keep
new file mode 100644
index 0000000000000..e69de29bb2d1d
diff --git a/clang/test/Driver/linux-musl-library-search.cpp b/clang/test/Driver/linux-musl-library-search.cpp
new file mode 100644
index 0000000000000..a8125aef73ab1
--- /dev/null
+++ b/clang/test/Driver/linux-musl-library-search.cpp
@@ -0,0 +1,14 @@
+// RUN: %clang -### %s 2>&1 \
+// RUN:     --target=aarch64-unknown-linux-musl \
+// RUN:     -ccc-install-dir %S/Inputs/basic_linux_tree/usr/bin \
+// RUN:     -resource-dir=%S/Inputs/resource_dir_empty \
+// RUN:     --sysroot=%S/Inputs/musl_sysroot_with_builtins \
+// RUN:   | FileCheck %s
+
+// CHECK-DAG: "--sysroot={{[^"]+}}/Inputs/musl_sysroot_with_builtins"
+// CHECK-DAG: "{{[^"]+}}/Inputs/musl_sysroot_with_builtins/lib/Scrt1.o"
+// CHECK-DAG: "{{[^"]+}}/Inputs/musl_sysroot_with_builtins/lib/crti.o"
+// CHECK-DAG: "{{[^"]+}}/Inputs/musl_sysroot_with_builtins/lib/clang_rt.crtbegin.o"
+// CHECK-DAG: "{{[^"]+}}/Inputs/musl_sysroot_with_builtins/lib/libclang_rt.builtins.a"
+// CHECK-DAG: "{{[^"]+}}/Inputs/musl_sysroot_with_builtins/lib/clang_rt.crtend.o"
+// CHECK-DAG: "{{[^"]+}}/Inputs/musl_sysroot_with_builtins/lib/crtn.o"

[MaskRay]

NAK.

(LibraryPaths is primarily intended for compiler-rt libraries.)

Maintaining compatibility by itself isn’t sufficient, as each entry could subtly shift library selection precedence, and the code here reflects a certain level of upstream (llvm-project) preference. We should ensure that the items listed align with typical Linux installations.

I don’t think that finding compiler-rt libraries in $sysroot/lib warrants changes to the Linux toolchain code. Moreover, we discourage such file hierarchies. This change could be problematic for cross compilation.

If your downstream setup demands this, consider installing symlinks.