[clang] [flang] [llvm] [flang][AArch64] Always link compiler-rt to flang after libgcc (PR #144710)

[Kiran Chandramohan via llvm-commits]

https://github.com/kiranchandramohan updated https://github.com/llvm/llvm-project/pull/144710

>From 2c278271277823b3544d991365e58f97dd4b7031 Mon Sep 17 00:00:00 2001
From: David Truby <david.truby at arm.com>
Date: Wed, 18 Jun 2025 10:17:05 +0100
Subject: [PATCH] [flang][AArch64] Always compiler-rt to flang linking after
 libgcc

This patch fixes an issue where the __trampoline_setup symbol is missing
with some programs compiled with flang. This symbol is present only in
compiler-rt and not in libgcc. This patch adds compiler-rt to the link
line after libgcc if libgcc is being used, so that only this symbol will
be picked from compiler-rt.
---
 clang/lib/Driver/ToolChains/CommonArgs.cpp | 7 +++++++
 flang/test/Driver/flang-ld-aarch64.f90     | 9 +++++++++
 llvm/CMakeLists.txt                        | 7 +++++++
 3 files changed, 23 insertions(+)
 create mode 100644 flang/test/Driver/flang-ld-aarch64.f90

diff --git a/clang/lib/Driver/ToolChains/CommonArgs.cpp b/clang/lib/Driver/ToolChains/CommonArgs.cpp
index d5b2c5c1e199e..672b73432847d 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ b/clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -2252,6 +2252,13 @@ static void AddLibgcc(const ToolChain &TC, const Driver &D,
   if (LGT == LibGccType::SharedLibGcc ||
       (LGT == LibGccType::UnspecifiedLibGcc && D.CCCIsCXX()))
     CmdArgs.push_back("-lgcc");
+  // compiler-rt is needed after libgcc for flang on AArch64 for the
+  // __trampoline_setup symbol
+  if (D.IsFlangMode() && TC.getArch() == llvm::Triple::aarch64) {
+    CmdArgs.push_back("--as-needed");
+    CmdArgs.push_back(TC.getCompilerRTArgString(Args, "builtins"));
+    CmdArgs.push_back("--no-as-needed");
+  }
 }
 
 void tools::AddRunTimeLibs(const ToolChain &TC, const Driver &D,
diff --git a/flang/test/Driver/flang-ld-aarch64.f90 b/flang/test/Driver/flang-ld-aarch64.f90
new file mode 100644
index 0000000000000..61cd46cea5cd1
--- /dev/null
+++ b/flang/test/Driver/flang-ld-aarch64.f90
@@ -0,0 +1,9 @@
+! Check linker flags for AArch64 linux, since it needs both libgcc and 
+! compiler-rt, with compiler-rt second when -rtlib=libgcc.
+
+! RUN: %flang -### -rtlib=libgcc --target=aarch64-linux-gnu %S/Inputs/hello.f90 2>&1 | FileCheck %s
+
+! CHECK-LABEL:  "{{.*}}ld{{(\.exe)?}}"
+! CHECK-SAME: "-lflang_rt.runtime" "-lm"
+! CHECK-SAME: "-lgcc" "--as-needed" "-lgcc_s" "--no-as-needed"
+! CHECK-SAME: "--as-needed" "{{.*}}{{\\|/}}libclang_rt.builtins.a" "--no-as-needed"
diff --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt
index 0849bec26d56a..1b91e45c202e3 100644
--- a/llvm/CMakeLists.txt
+++ b/llvm/CMakeLists.txt
@@ -653,6 +653,13 @@ if(LLVM_EXPERIMENTAL_TARGETS_TO_BUILD STREQUAL "all")
   set(LLVM_EXPERIMENTAL_TARGETS_TO_BUILD ${LLVM_ALL_EXPERIMENTAL_TARGETS})
 endif()
 
+if("flang" IN_LIST LLVM_ENABLE_PROJECTS AND 
+   "AArch64" IN_LIST LLVM_TARGETS_TO_BUILD AND
+   NOT "compiler-rt" IN_LIST LLVM_ENABLE_RUNTIMES)
+  message(STATUS "Enabling Flang-RT as a dependency of Flang")
+  list(APPEND LLVM_ENABLE_RUNTIMES "compiler-rt")
+endif()
+
 set(LLVM_TARGETS_TO_BUILD
    ${LLVM_TARGETS_TO_BUILD}
    ${LLVM_EXPERIMENTAL_TARGETS_TO_BUILD})