Index: llvm/include/llvm/BinaryFormat/XCOFF.h
===================================================================
--- llvm/include/llvm/BinaryFormat/XCOFF.h
+++ llvm/include/llvm/BinaryFormat/XCOFF.h
@@ -27,6 +27,7 @@
 constexpr size_t NameSize = 8;
 constexpr size_t SymbolTableEntrySize = 18;
 constexpr size_t RelocationSerializationSize32 = 10;
+constexpr uint16_t RelocOverflow = 65535;
 
 enum ReservedSectionNum : int16_t { N_DEBUG = -2, N_ABS = -1, N_UNDEF = 0 };
 
Index: llvm/lib/MC/XCOFFObjectWriter.cpp
===================================================================
--- llvm/lib/MC/XCOFFObjectWriter.cpp
+++ llvm/lib/MC/XCOFFObjectWriter.cpp
@@ -740,8 +740,16 @@
       if (Group->empty())
         continue;
 
-      for (auto &Csect : *Group)
+      for (auto &Csect : *Group) {
+        if (Csect.Relocations.size() >= XCOFF::RelocOverflow ||
+            Section->RelocationCount >=
+                XCOFF::RelocOverflow - Csect.Relocations.size())
+          report_fatal_error(
+              "relocation entries overflowed; overflow section is "
+              "not implemented yet");
+
         Section->RelocationCount += Csect.Relocations.size();
+      }
     }
   }
 
Index: llvm/lib/Object/XCOFFObjectFile.cpp
===================================================================
--- llvm/lib/Object/XCOFFObjectFile.cpp
+++ llvm/lib/Object/XCOFFObjectFile.cpp
@@ -20,7 +20,6 @@
 
 static const uint8_t FunctionSym = 0x20;
 static const uint8_t SymTypeMask = 0x07;
-static const uint16_t RelocOverflow = 65535;
 static const uint16_t NoRelMask = 0x0001;
 
 // Checks that [Ptr, Ptr + Size) bytes fall inside the memory buffer
@@ -632,7 +631,7 @@
 
   uint16_t SectionIndex = &Sec - sectionHeaderTable32() + 1;
 
-  if (Sec.NumberOfRelocations < RelocOverflow)
+  if (Sec.NumberOfRelocations < XCOFF::RelocOverflow)
     return Sec.NumberOfRelocations;
   for (const auto &Sec : sections32()) {
     if (Sec.Flags == XCOFF::STYP_OVRFLO &&
Index: llvm/test/CodeGen/PowerPC/aix-xcoff-huge-relocs.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/PowerPC/aix-xcoff-huge-relocs.ll
@@ -0,0 +1,44 @@
+;; This test generates 65535 relocation entries in a single section,
+;; which would trigger an overflow section to be generated in 32-bit mode.
+;; Since overflow section is not supported yet, we will emit an error instead of
+;; generating an invalid binary for now.
+; RUN: grep -v RUN: %s | \
+; RUN:   sed >%t.overflow.ll 's/SIZE/65535/;s/MACRO/#/;s/#/################/g;s/#/################/g;s/#/################/g;s/#/################/g;s/#/#_/g;s/_#_\([^#]\)/\1/;s/_/, /g;s/#/i8* @c/g;'
+; RUN: not --crash llc -verify-machineinstrs -mtriple powerpc-ibm-aix-xcoff \
+; RUN:     -mcpu=pwr4 -mattr=-altivec -filetype=obj -o %t.o %t.overflow.ll 2>&1 | \
+; RUN:   FileCheck --check-prefix=OVERFLOW %s
+; OVERFLOW: LLVM ERROR: relocation entries overflowed; overflow section is not implemented yet
+
+;; This test generates 65534 relocation entries, an overflow section should 
+;; not be generated.
+; RUN: grep -v RUN: %s | \
+; RUN:   sed >%t.ll 's/SIZE/65534/;s/MACRO/#/;s/#/################/g;s/#/################/g;s/#/################/g;s/#/################/g;s/#/#_/g;s/_#_#_\([^#]\)/\1/;s/_/, /g;s/#/i8* @c/g;'
+; RUN: llc -verify-machineinstrs -mtriple powerpc-ibm-aix-xcoff \
+; RUN:     -mcpu=pwr4 -mattr=-altivec -filetype=obj -o %t.o %t.ll
+; RUN: llvm-readobj --section-headers %t.o | FileCheck --check-prefix=XCOFF32 %s
+
+; RUN: not --crash llc -verify-machineinstrs -mtriple powerpc64-ibm-aix-xcoff \
+; RUN:     -mcpu=pwr4 -mattr=-altivec -filetype=obj -o %t.o %t.overflow.ll 2>&1 | \
+; RUN:   FileCheck --check-prefix=XCOFF64 %s
+; RUN: not --crash llc -verify-machineinstrs -mtriple powerpc64-ibm-aix-xcoff \
+; RUN:     -mcpu=pwr4 -mattr=-altivec -filetype=obj -o %t.o %t.ll 2>&1 | \
+; RUN:   FileCheck --check-prefix=XCOFF64 %s
+; XCOFF64: LLVM ERROR: 64-bit XCOFF object files are not supported yet.
+
+@c = external global i8, align 1
+@arr = global [SIZE x i8*] [MACRO], align 8
+
+; XCOFF32-NOT:     Name: .ovrflo
+; XCOFF32-NOT:     Type: STYP_OVRFLO
+; XCOFF32:       Section {
+; XCOFF32:         Name: .data
+; XCOFF32-NEXT:    PhysicalAddress: 0x0
+; XCOFF32-NEXT:    VirtualAddress: 0x0
+; XCOFF32-NEXT:    Size: 0x3FFF8
+; XCOFF32-NEXT:    RawDataOffset: 0x64
+; XCOFF32-NEXT:    RelocationPointer: 0x4005C
+; XCOFF32-NEXT:    LineNumberPointer: 0x0
+; XCOFF32-NEXT:    NumberOfRelocations: 65534
+; XCOFF32-NEXT:    NumberOfLineNumbers: 0
+; XCOFF32-NEXT:    Type: STYP_DATA (0x40)
+; XCOFF32-NEXT:  }