[clang] [Clang][Driver] Override Generic_ELF::buildLinker() to avoid calling gcc to link (PR #149681)

[via cfe-commits]

https://github.com/mintsuki updated https://github.com/llvm/llvm-project/pull/149681

>From 468635d12a26a7e1d38fe9d1321a5f76167ddead Mon Sep 17 00:00:00 2001
From: Mintsuki <mintsuki at protonmail.com>
Date: Sun, 20 Jul 2025 00:21:08 +0200
Subject: [PATCH] [Clang][Driver] Override Generic_ELF::buildLinker() to avoid
 calling gcc to link

This change primarily makes it so that when targeting freestanding/unknown
OSes, the driver will not use `gcc` to link, but rather will link using
the chosen linker (`-fuse-ld=...`) directly.

If Clang is to be a cross compiler, there is no reason to assume that the
host's gcc is in any way capable of handling the linkage of programs for
targets that do not match the host's triple, especially for freestanding
targets.
---
 clang/lib/Driver/ToolChains/Gnu.cpp |  2 ++
 clang/lib/Driver/ToolChains/Gnu.h   |  3 +++
 clang/test/Driver/baremetal-ld.c    | 11 +++++++++++
 3 files changed, 16 insertions(+)

diff --git a/clang/lib/Driver/ToolChains/Gnu.cpp b/clang/lib/Driver/ToolChains/Gnu.cpp
index f5e2655857432..4beb67f888a7c 100644
--- a/clang/lib/Driver/ToolChains/Gnu.cpp
+++ b/clang/lib/Driver/ToolChains/Gnu.cpp
@@ -3375,3 +3375,5 @@ void Generic_ELF::addClangTargetOptions(const ArgList &DriverArgs,
                           options::OPT_fno_use_init_array, true))
     CC1Args.push_back("-fno-use-init-array");
 }
+
+Tool *Generic_ELF::buildLinker() const { return new tools::gnutools::Linker(*this); }
diff --git a/clang/lib/Driver/ToolChains/Gnu.h b/clang/lib/Driver/ToolChains/Gnu.h
index 3b8df71bbf9d3..152a7ab8d5289 100644
--- a/clang/lib/Driver/ToolChains/Gnu.h
+++ b/clang/lib/Driver/ToolChains/Gnu.h
@@ -382,6 +382,9 @@ class LLVM_LIBRARY_VISIBILITY Generic_ELF : public Generic_GCC {
   }
 
   virtual void addExtraOpts(llvm::opt::ArgStringList &CmdArgs) const {}
+
+protected:
+  Tool *buildLinker() const override;
 };
 
 } // end namespace toolchains
diff --git a/clang/test/Driver/baremetal-ld.c b/clang/test/Driver/baremetal-ld.c
index ec61b42b6f487..be2d942acb392 100644
--- a/clang/test/Driver/baremetal-ld.c
+++ b/clang/test/Driver/baremetal-ld.c
@@ -4,3 +4,14 @@
 
 // RUN: %clang -### --target=armv7-unknown-none-eabi -mcpu=cortex-m4 --sysroot= -fuse-ld=ld -flto -O3 %s 2>&1 | FileCheck --check-prefix=LTO %s
 // LTO: {{".*ld.*"}} {{.*}} "-plugin-opt=mcpu=cortex-m4" "-plugin-opt=O3"
+
+// Ensure that, for freestanding -none targets, the linker does not call into gcc.
+// We do this by checking if clang is trying to pass "-fuse-ld=bfd" to the linker command.
+// RUN: %clang -### --target=aarch64-unknown-none-elf -fuse-ld=bfd %s 2>&1 | FileCheck --check-prefix=FUSELDAARCH64 %s
+// FUSELDAARCH64-NOT: "-fuse-ld=bfd"
+// RUN: %clang -### --target=loongarch64-unknown-none-elf -fuse-ld=bfd %s 2>&1 | FileCheck --check-prefix=FUSELDLOONGARCH64 %s
+// FUSELDLOONGARCH64-NOT: "-fuse-ld=bfd"
+// RUN: %clang -### --target=riscv64-unknown-none-elf -fuse-ld=bfd %s 2>&1 | FileCheck --check-prefix=FUSELDRISCV64 %s
+// FUSELDRISCV64-NOT: "-fuse-ld=bfd"
+// RUN: %clang -### --target=x86_64-unknown-none-elf -fuse-ld=bfd %s 2>&1 | FileCheck --check-prefix=FUSELDX8664 %s
+// FUSELDX8664-NOT: "-fuse-ld=bfd"