diff --git a/llvm/lib/MC/MCMachOStreamer.cpp b/llvm/lib/MC/MCMachOStreamer.cpp
--- a/llvm/lib/MC/MCMachOStreamer.cpp
+++ b/llvm/lib/MC/MCMachOStreamer.cpp
@@ -31,6 +31,7 @@
 #include "llvm/MC/TargetRegistry.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/LEB128.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cassert>
 #include <vector>
@@ -593,5 +594,9 @@
   MCSection *AddrSigSection =
       Asm.getContext().getObjectFileInfo()->getAddrSigSection();
   Asm.registerSection(*AddrSigSection);
-  new MCDataFragment(AddrSigSection);
+  auto *Frag = new MCDataFragment(AddrSigSection);
+  size_t SectionBytes = 0;
+  for (const MCSymbol *sym : writer.getAddrsigSyms())
+    SectionBytes += getULEB128Size(sym->getIndex());
+  Frag->getContents().resize(SectionBytes);
 }
diff --git a/llvm/lib/MC/MachObjectWriter.cpp b/llvm/lib/MC/MachObjectWriter.cpp
--- a/llvm/lib/MC/MachObjectWriter.cpp
+++ b/llvm/lib/MC/MachObjectWriter.cpp
@@ -766,6 +766,7 @@
   MCDataFragment *pDataFragment = dyn_cast_or_null<MCDataFragment>(pFragment);
   assert(pDataFragment);
 
+  pDataFragment->getContents().clear();
   raw_svector_ostream OS(pDataFragment->getContents());
   for (const MCSymbol *sym : this->getAddrsigSyms())
     encodeULEB128(sym->getIndex(), OS);
diff --git a/llvm/test/CodeGen/AArch64/addrsig-macho.ll b/llvm/test/CodeGen/AArch64/addrsig-macho.ll
--- a/llvm/test/CodeGen/AArch64/addrsig-macho.ll
+++ b/llvm/test/CodeGen/AArch64/addrsig-macho.ll
@@ -1,7 +1,16 @@
 ; RUN: llc -filetype=asm %s -o - -mtriple arm64-apple-ios -addrsig | FileCheck %s
 ; RUN: llc -filetype=obj %s -o %t -mtriple arm64-apple-ios -addrsig
+; RUN: llvm-objdump --macho --section-headers %t | FileCheck %s --check-prefix=SECTIONS
 ; RUN: llvm-readobj --hex-dump='__llvm_addrsig' %t | FileCheck %s --check-prefix=OBJ
 
+; The __debug_line section (which should be generated for the given input file)
+; should appear immediately after the addrsig section.  Use it to make sure
+; addrsig's section size has been properly set during section layout. This
+; catches a regression where the next section would overlap addrsig's
+; contents.
+; SECTIONS:      __llvm_addrsig [[#%.8x,SIZE:]] [[#%.16x,ADDR:]]
+; SECTIONS-NEXT: __debug_line   {{[[:xdigit:]]+}} [[#%.16x, SIZE+ADDR]]
+
 ; CHECK:			.addrsig{{$}}
 ; CHECK-NEXT:	.addrsig_sym _func03_takeaddr
 ; CHECK-NEXT:	.addrsig_sym _f1
@@ -38,7 +47,7 @@
 }
 
 ; Function Attrs: minsize nofree noinline norecurse nounwind optsize ssp uwtable
-define void @func03_takeaddr() #0 {
+define void @func03_takeaddr() #0 !dbg !9 {
 entry:
   %0 = load volatile i32, ptr @result, align 4
   %add = add nsw i32 %0, 1
@@ -72,8 +81,8 @@
   %a2 = bitcast i32* @a2 to i8*
   %i1 = bitcast void()* @i1 to i8*
   %i2 = bitcast void()* @i2 to i8*
-  call void @llvm.dbg.value(metadata i8* bitcast (void()* @metadata_f1 to i8*), metadata !5, metadata !DIExpression()), !dbg !7
-  call void @llvm.dbg.value(metadata i8* bitcast (void()* @metadata_f2 to i8*), metadata !5, metadata !DIExpression()), !dbg !7
+  call void @llvm.dbg.value(metadata i8* bitcast (void()* @metadata_f1 to i8*), metadata !6, metadata !DIExpression()), !dbg !8
+  call void @llvm.dbg.value(metadata i8* bitcast (void()* @metadata_f2 to i8*), metadata !6, metadata !DIExpression()), !dbg !8
   call void @f4(i8* bitcast (void()* @metadata_f2 to i8*))
   unreachable
 }
@@ -108,9 +117,18 @@
 declare void @llvm.dbg.value(metadata, metadata, metadata)
 
 attributes #0 = { noinline }
-
-!3 = distinct !DISubprogram(scope: null, isLocal: false, isDefinition: true, isOptimized: false)
-!4 = !DILocation(line: 0, scope: !3)
-!5 = !DILocalVariable(scope: !6)
-!6 = distinct !DISubprogram(scope: null, isLocal: false, isDefinition: true, isOptimized: false)
-!7 = !DILocation(line: 0, scope: !6, inlinedAt: !4)
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, emissionKind: FullDebug)
+!1 = !DIFile(filename: "test.c", directory: "/tmp")
+!2 = !{i32 7, !"Dwarf Version", i32 4}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+
+!4 = distinct !DISubprogram(scope: null, isLocal: false, isDefinition: true, isOptimized: false, unit: !0)
+!5 = !DILocation(line: 0, scope: !4)
+!6 = !DILocalVariable(scope: !7)
+!7 = distinct !DISubprogram(scope: null, isLocal: false, isDefinition: true, isOptimized: false, unit: !0)
+!8 = !DILocation(line: 0, scope: !7, inlinedAt: !5)
+!9 = distinct !DISubprogram(scope: null, file: !1, line: 1, type: !10, unit: !0)
+!10 = !DISubroutineType(types: !{})