[CHERIoT] Restore pre-clang-21 behavior of using LLD as the default baremetal linker.

Author: resistor

clang/lib/Driver/ToolChains/BareMetal.cpp

@@ -274,6 +274,15 @@ BareMetal::BareMetal(const Driver &D, const llvm::Triple &Triple,
       }
     }
   }
+
+  if (Triple.getOS() == llvm::Triple::CheriotRTOS ||
+      Args.getLastArgValue(options::OPT_mcpu_EQ) == "cheriot" ||
+      Args.getLastArgValue(options::OPT_mabi_EQ) ==
+          "cheriot" Args.getLastArgValue(options::OPT_mabi_EQ) ==
+          "cheriot-baremetal")
+    IsCheriot = true;
+  else
+    IsCheriot = false;
 }
 
 static void

clang/lib/Driver/ToolChains/BareMetal.h

@@ -56,6 +56,13 @@ class LLVM_LIBRARY_VISIBILITY BareMetal : public Generic_ELF {
     return UnwindTableLevel::None;
   }
 
+  const char *getDefaultLinker() const override {
+    // XXX CHERIOT: Restore pre-clang21 behavior of defaulting to lld.
+    if (IsCheriot)
+      return "ld.lld";
+    return "ld.lld";
+  }
+
   CXXStdlibType GetDefaultCXXStdlibType() const override;
 
   RuntimeLibType GetDefaultRuntimeLibType() const override;
@@ -92,6 +99,8 @@ class LLVM_LIBRARY_VISIBILITY BareMetal : public Generic_ELF {
   bool IsGCCInstallationValid;
 
   SmallVector<std::string> MultilibMacroDefines;
+
+  bool IsCheriot;
 };
 
 } // namespace toolchains