Index: ELF/LinkerScript.h
===================================================================
--- ELF/LinkerScript.h
+++ ELF/LinkerScript.h
@@ -131,6 +131,7 @@
   int compareSections(StringRef A, StringRef B);
   void addScriptedSymbols();
   bool hasPhdrsCommands();
+  uintX_t getOutputSectionSize(StringRef Name);
 
 private:
   std::vector<std::pair<StringRef, const InputSectionDescription *>>
@@ -150,6 +151,7 @@
   size_t getPhdrIndex(StringRef PhdrName);
   void dispatchAssignment(SymbolAssignment *Cmd);
 
+  OutputSectionFactory<ELFT> *Factory = nullptr;
   uintX_t Dot;
 };
 
Index: ELF/LinkerScript.cpp
===================================================================
--- ELF/LinkerScript.cpp
+++ ELF/LinkerScript.cpp
@@ -112,6 +112,7 @@
 template <class ELFT>
 std::vector<OutputSectionBase<ELFT> *>
 LinkerScript<ELFT>::createSections(OutputSectionFactory<ELFT> &Factory) {
+  this->Factory = &Factory;
   std::vector<OutputSectionBase<ELFT> *> Ret;
 
   // Add input section to output section. If there is no output section yet,
@@ -380,6 +381,15 @@
   return !Opt.PhdrsCommands.empty();
 }
 
+template <class ELFT>
+typename ELFT::uint LinkerScript<ELFT>::getOutputSectionSize(StringRef Name) {
+  for (const std::unique_ptr<OutputSectionBase<ELFT>>& OutSec : Factory->getOwningSections())
+    if (OutSec->getName() == Name)
+      return OutSec->getSize();
+  error("undefined section " + Name);
+  return 0;
+}
+
 // Returns indices of ELF headers containing specific section, identified
 // by Name. Each index is a zero based number of ELF header listed within
 // PHDRS {} script block.
@@ -810,6 +820,22 @@
   return 0;
 }
 
+static uint64_t getSectionSize(StringRef Name) {
+  switch (Config->EKind) {
+  case ELF32LEKind:
+    return Script<ELF32LE>::X->getOutputSectionSize(Name);
+  case ELF32BEKind:
+    return Script<ELF32BE>::X->getOutputSectionSize(Name);
+  case ELF64LEKind:
+    return Script<ELF64LE>::X->getOutputSectionSize(Name);
+  case ELF64BEKind:
+    return Script<ELF64BE>::X->getOutputSectionSize(Name);
+  default:
+    llvm_unreachable("unsupported target");
+  }
+  return 0;
+}
+
 // This is a part of the operator-precedence parser. This function
 // assumes that the remaining token stream starts with an operator.
 Expr ScriptParser::readExpr1(Expr Lhs, int MinPrec) {
@@ -897,6 +923,12 @@
     expect(")");
     return [](uint64_t Dot) { return alignTo(Dot, Target->PageSize); };
   }
+  if (Tok == "SIZEOF") {
+    expect("(");
+    StringRef Name = next();
+    expect(")");
+    return [=](uint64_t Dot) { return getSectionSize(Name); };
+  }
 
   // Parse a symbol name or a number literal.
   uint64_t V = 0;
Index: ELF/OutputSections.h
===================================================================
--- ELF/OutputSections.h
+++ ELF/OutputSections.h
@@ -681,6 +681,9 @@
                                                     StringRef OutsecName);
 
   OutputSectionBase<ELFT> *lookup(StringRef Name, uint32_t Type, uintX_t Flags);
+  llvm::ArrayRef<std::unique_ptr<OutputSectionBase<ELFT>>> getOwningSections() {
+    return OwningSections;
+  }
 
 private:
   Key createKey(InputSectionBase<ELFT> *C, StringRef OutsecName);
Index: test/ELF/linkerscript/linkerscript-sizeof.s
===================================================================
--- test/ELF/linkerscript/linkerscript-sizeof.s
+++ test/ELF/linkerscript/linkerscript-sizeof.s
@@ -0,0 +1,53 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+
+# RUN: echo "SECTIONS { \
+# RUN:   .aaa         : { *(.aaa) } \
+# RUN:   .bbb         : { *(.bbb) } \
+# RUN:   .ccc         : { *(.ccc) } \
+# RUN:   _aaa = SIZEOF(.aaa); \
+# RUN:   _bbb = SIZEOF(.bbb); \
+# RUN:   _ccc = SIZEOF(.ccc); \
+# RUN: }" > %t.script
+# RUN: ld.lld -o %t1 --script %t.script %t
+# RUN: llvm-objdump -t -section-headers %t1 | FileCheck %s
+# CHECK:      Sections:
+# CHECK-NEXT:  Idx Name          Size      Address          Type
+# CHECK-NEXT:    0               00000000 0000000000000000
+# CHECK-NEXT:    1 .aaa          00000008 0000000000000120 DATA
+# CHECK-NEXT:    2 .bbb          00000010 0000000000000128 DATA
+# CHECK-NEXT:    3 .ccc          00000018 0000000000000138 DATA
+# CHECK:      SYMBOL TABLE:
+# CHECK-NEXT:  0000000000000000 *UND* 00000000
+# CHECK-NEXT:  0000000000000150 .text 00000000 _start
+# CHECK-NEXT:  0000000000000008 *ABS* 00000000 _aaa
+# CHECK-NEXT:  0000000000000010 *ABS* 00000000 _bbb
+# CHECK-NEXT:  0000000000000018 *ABS* 00000000 _ccc
+
+## Check that we error out if trying to get size of
+## section that does not exist.
+# RUN: echo "SECTIONS { \
+# RUN:   .aaa         : { *(.aaa) } \
+# RUN:   .bbb         : { *(.bbb) } \
+# RUN:   .ccc         : { *(.ccc) } \
+# RUN:   _aaa = SIZEOF(.foo); \
+# RUN: }" > %t.script
+# RUN: not ld.lld -o %t1 --script %t.script %t 2>&1 \
+# RUN:  | FileCheck -check-prefix=ERR %s
+# ERR: undefined section .foo
+
+.global _start
+_start:
+ nop
+
+.section .aaa,"a"
+ .quad 0
+
+.section .bbb,"a"
+ .quad 0
+ .quad 0
+
+.section .ccc,"a"
+ .quad 0
+ .quad 0
+ .quad 0