[clang] [Clang] Link libgcc_s.1.dylib when building for macOS 10.5 and older (PR #124651)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-driver

Author: None (Un1q32)

<details>
<summary>Changes</summary>

There are a lot of symbols that the compiler expects to be in libSystem that were only in libgcc_s before 10.6, like libunwind things and some builtins on i386.  We already do this for iOS versions < 5.0 for the same reason.

---
Full diff: https://github.com/llvm/llvm-project/pull/124651.diff


2 Files Affected:

- (modified) clang/lib/Driver/ToolChains/Darwin.cpp (+5-4) 
- (modified) clang/test/Driver/darwin-ld.c (+6-1) 


``````````diff
diff --git a/clang/lib/Driver/ToolChains/Darwin.cpp b/clang/lib/Driver/ToolChains/Darwin.cpp
index 55c55bad739347..67f27a599b4c38 100644
--- a/clang/lib/Driver/ToolChains/Darwin.cpp
+++ b/clang/lib/Driver/ToolChains/Darwin.cpp
@@ -1645,12 +1645,13 @@ void DarwinClang::AddLinkRuntimeLibArgs(const ArgList &Args,
     CmdArgs.push_back("-lSystem");
 
   // Select the dynamic runtime library and the target specific static library.
-  if (isTargetIOSBased()) {
+  if (isTargetIOSBased() || isTargetMacOSBased()) {
     // If we are compiling as iOS / simulator, don't attempt to link libgcc_s.1,
     // it never went into the SDK.
-    // Linking against libgcc_s.1 isn't needed for iOS 5.0+
-    if (isIPhoneOSVersionLT(5, 0) && !isTargetIOSSimulator() &&
-        getTriple().getArch() != llvm::Triple::aarch64)
+    // Linking against libgcc_s.1 isn't needed for iOS 5.0+ or macOS 10.6+
+    if ((isIPhoneOSVersionLT(5, 0) && !isTargetIOSSimulator() &&
+         getTriple().getArch() != llvm::Triple::aarch64) ||
+        isMacosxVersionLT(10, 6))
       CmdArgs.push_back("-lgcc_s.1");
   }
   AddLinkRuntimeLib(Args, CmdArgs, "builtins");
diff --git a/clang/test/Driver/darwin-ld.c b/clang/test/Driver/darwin-ld.c
index f0ca411430cc78..5b10daaf007a2f 100644
--- a/clang/test/Driver/darwin-ld.c
+++ b/clang/test/Driver/darwin-ld.c
@@ -240,6 +240,11 @@
 // RUN: FileCheck -check-prefix=LINK_NO_IOS_ARM64_LIBGCC_S %s < %t.log
 // LINK_NO_IOS_ARM64_LIBGCC_S-NOT: lgcc_s.1
 
+// Check that clang links with libgcc_s.1 for macOS 10.5 and earlier
+// RUN: %clang -target x86_64-apple-macos10.5 -mmacosx-version-min=10.5 -### %t.o 2> %t.log
+// RUN: FileCheck -check-prefix=LINK_OSX_LIBGCC_S %s < %t.log
+// LINK_OSX_LIBGCC_S: lgcc_s.1
+
 // RUN: %clang -target x86_64-apple-darwin12 -rdynamic -### %t.o \
 // RUN:   -fuse-ld= -mlinker-version=100 2> %t.log
 // RUN: FileCheck -check-prefix=LINK_NO_EXPORT_DYNAMIC %s < %t.log
@@ -385,4 +390,4 @@
 // RUN:   %clang -target armv7em-apple-darwin -mno-outline -### %t.o 2> %t.log
 // RUN: FileCheck -check-prefix=ARMV7EM-MNO_OUTLINE %s < %t.log
 // ARMV7EM-MNO_OUTLINE: {{ld(.exe)?"}}
-// ARMV7EM-MNO_OUTLINE-SAME: "-mllvm" "-enable-machine-outliner=never" "-mllvm" "-enable-linkonceodr-outlining"
\ No newline at end of file
+// ARMV7EM-MNO_OUTLINE-SAME: "-mllvm" "-enable-machine-outliner=never" "-mllvm" "-enable-linkonceodr-outlining"

``````````

</details>


https://github.com/llvm/llvm-project/pull/124651