Index: llvm/docs/LangRef.rst
===================================================================
--- llvm/docs/LangRef.rst
+++ llvm/docs/LangRef.rst
@@ -7092,6 +7092,15 @@
     %a.addr = alloca float*, align 8, !annotation !0
     !0 = !{!"auto-init"}
 
+'``explicit_size``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The ``explicit_size`` metadata is used to emit a size directive with a different
+size than the objects total size. This can be useful when an object contains
+more bytes than are actually accessible or meaninfully part of the object. It
+will emit any size given without any error checking, even if that size isn't
+meaningful.
+
 Module Flags Metadata
 =====================
 
Index: llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
===================================================================
--- llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -690,10 +690,21 @@
 
   emitGlobalConstant(GV->getParent()->getDataLayout(), GV->getInitializer());
 
-  if (MAI->hasDotTypeDotSizeDirective())
+  if (MAI->hasDotTypeDotSizeDirective()) {
+    [&Size, GV] {
+      const MDNode *ExplicitValue = GV->getMetadata("explicit_size");
+      if (!ExplicitValue || !ExplicitValue->getNumOperands())
+        return;
+      const auto *MetadataValue = dyn_cast<ValueAsMetadata>(ExplicitValue->getOperand(0));
+      if (!MetadataValue)
+        return;
+      if (const auto *CI = dyn_cast<ConstantInt>(MetadataValue->getValue()))
+        Size = CI->getZExtValue();
+    }();
     // .size foo, 42
     OutStreamer->emitELFSize(EmittedInitSym,
                              MCConstantExpr::create(Size, OutContext));
+  }
 
   OutStreamer->AddBlankLine();
 }
Index: llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
===================================================================
--- llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
+++ llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
@@ -2510,6 +2510,11 @@
     // zero so we can copy the metadata over as is.
     NewGlobal->copyMetadata(G, 0);
 
+    LLVMContext &C = NewGlobal->getContext();
+    ConstantInt *Int = ConstantInt::get(C, APInt{64, SizeInBytes});
+    MDNode *N = MDNode::get(C, ConstantAsMetadata::get(Int));
+    NewGlobal->setMetadata("explicit_size", N);
+
     Value *Indices2[2];
     Indices2[0] = IRB.getInt32(0);
     Indices2[1] = IRB.getInt32(0);
Index: llvm/test/CodeGen/X86/explicit-size-metadata.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/X86/explicit-size-metadata.ll
@@ -0,0 +1,12 @@
+; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu | FileCheck %s
+
+@a = dso_local global i64 0, align 8, !explicit_size !0
+; CHECK: .size a, 4
+
+@b = dso_local global i64 0, align 8
+; CHECK: .size b, 8
+
+@larger = dso_local global i16 0, align 4, !explicit_size !0
+; CHECK: .size larger, 4
+
+!0 = !{i64 4}
Index: llvm/test/Instrumentation/AddressSanitizer/adaptive_global_redzones.ll
===================================================================
--- llvm/test/Instrumentation/AddressSanitizer/adaptive_global_redzones.ll
+++ llvm/test/Instrumentation/AddressSanitizer/adaptive_global_redzones.ll
@@ -6,14 +6,14 @@
 ; Here we check that the global redzone sizes grow with the object size.
 
 @G10 = global [10 x i8] zeroinitializer, align 1
-; CHECK: @G10 = global { [10 x i8], [22 x i8] }
+; CHECK: @G10 = global { [10 x i8], [22 x i8] } zeroinitializer, align 32, !explicit_size ![[TAG10:.*]]
 
 @G31 = global [31 x i8] zeroinitializer, align 1
 @G32 = global [32 x i8] zeroinitializer, align 1
 @G33 = global [33 x i8] zeroinitializer, align 1
-; CHECK: @G31 = global { [31 x i8], [33 x i8] }
-; CHECK: @G32 = global { [32 x i8], [32 x i8] }
-; CHECK: @G33 = global { [33 x i8], [63 x i8] }
+; CHECK: @G31 = global { [31 x i8], [33 x i8] } zeroinitializer, align 32, !explicit_size ![[TAG31:.*]]
+; CHECK: @G32 = global { [32 x i8], [32 x i8] } zeroinitializer, align 32, !explicit_size ![[TAG32:.*]]
+; CHECK: @G33 = global { [33 x i8], [63 x i8] } zeroinitializer, align 32, !explicit_size ![[TAG33:.*]]
 
 @G63 = global [63 x i8] zeroinitializer, align 1
 @G64 = global [64 x i8] zeroinitializer, align 1
@@ -55,4 +55,10 @@
 @G100000000 = global [100000000 x i8] zeroinitializer, align 1
 ; CHECK: @G1000000 = global { [1000000 x i8], [249984 x i8] }
 ; CHECK: @G10000000 = global { [10000000 x i8], [262144 x i8] }
-; CHECK: @G100000000 = global { [100000000 x i8], [262144 x i8] }
+; CHECK: @G100000000 = global { [100000000 x i8], [262144 x i8] } zeroinitializer, align 32, !explicit_size ![[TAGBIG:.*]]
+
+; CHECK: ![[TAG10]] = !{i64 10}
+; CHECK: ![[TAG31]] = !{i64 31}
+; CHECK: ![[TAG32]] = !{i64 32}
+; CHECK: ![[TAG33]] = !{i64 33}
+; CHECK: ![[TAGBIG]] = !{i64 100000000}
Index: llvm/test/Instrumentation/AddressSanitizer/debug-info-global-var.ll
===================================================================
--- llvm/test/Instrumentation/AddressSanitizer/debug-info-global-var.ll
+++ llvm/test/Instrumentation/AddressSanitizer/debug-info-global-var.ll
@@ -2,7 +2,7 @@
 source_filename = "version.c"
 target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-apple-macosx10.12.0"
-; CHECK: @version = constant { [5 x i8], [27 x i8] } {{.*}}, !dbg ![[GV:.*]]
+; CHECK: @version = constant { [5 x i8], [27 x i8] } {{.*}}, !dbg ![[GV:.*]],
 
 @version = constant [5 x i8] c"4.00\00", align 1, !dbg !0