Index: lld/ELF/Arch/AVR.cpp
===================================================================
--- lld/ELF/Arch/AVR.cpp
+++ lld/ELF/Arch/AVR.cpp
@@ -43,6 +43,7 @@
 class AVR final : public TargetInfo {
 public:
   AVR();
+  uint32_t calcEFlags() const override;
   RelExpr getRelExpr(RelType type, const Symbol &s,
                      const uint8_t *loc) const override;
   void relocate(uint8_t *loc, const Relocation &rel,
@@ -196,3 +197,30 @@
   static AVR target;
   return ⌖
 }
+
+static uint32_t getEFlags(InputFile *file) {
+  return cast<ObjFile<ELF32LE>>(file)->getObj().getHeader().e_flags;
+}
+
+uint32_t AVR::calcEFlags() const {
+  assert(!objectFiles.empty());
+
+  uint32_t flags = getEFlags(objectFiles[0]);
+  bool hasLinkerRelaxFlag = flags & EF_AVR_LINKRELAX_PREPARED;
+
+  for (InputFile *f : makeArrayRef(objectFiles).slice(1)) {
+    uint32_t objFlags = getEFlags(f);
+
+    if ((objFlags & EF_AVR_ARCH_MASK) != (flags & EF_AVR_ARCH_MASK))
+      error(toString(f) +
+            ": cannot link object files with incompatible target ISA");
+
+    if (!(objFlags & EF_AVR_LINKRELAX_PREPARED))
+      hasLinkerRelaxFlag = false;
+  }
+
+  if (!hasLinkerRelaxFlag)
+    flags &= ~EF_AVR_LINKRELAX_PREPARED;
+
+  return flags;
+}
Index: llvm/include/llvm/BinaryFormat/ELF.h
===================================================================
--- llvm/include/llvm/BinaryFormat/ELF.h
+++ llvm/include/llvm/BinaryFormat/ELF.h
@@ -484,7 +484,12 @@
   EF_AVR_ARCH_XMEGA4 = 104,
   EF_AVR_ARCH_XMEGA5 = 105,
   EF_AVR_ARCH_XMEGA6 = 106,
-  EF_AVR_ARCH_XMEGA7 = 107
+  EF_AVR_ARCH_XMEGA7 = 107,
+
+  EF_AVR_ARCH_MASK = 0x7f, // EF_AVR_ARCH_xxx selection mask
+
+  EF_AVR_LINKRELAX_PREPARED = 0x80, // The file is prepared for linker
+                                    // relaxation to be applied
 };
 
 // ELF Relocation types for AVR