diff --git a/llvm/lib/MC/ELFObjectWriter.cpp b/llvm/lib/MC/ELFObjectWriter.cpp
--- a/llvm/lib/MC/ELFObjectWriter.cpp
+++ b/llvm/lib/MC/ELFObjectWriter.cpp
@@ -47,6 +47,7 @@
 #include "llvm/Support/LEB128.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/SMLoc.h"
+#include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/StringSaver.h"
 #include "llvm/Support/SwapByteOrder.h"
 #include "llvm/Support/raw_ostream.h"
@@ -169,8 +170,13 @@
 
   void writeHeader(const MCAssembler &Asm);
 
-  void writeSymbol(SymbolTableWriter &Writer, uint32_t StringIndex,
-                   ELFSymbolData &MSD, const MCAsmLayout &Layout);
+
+  void writeSymbol(MCAssembler &Asm, SymbolTableWriter &Writer,
+                   uint32_t StringIndex, ELFSymbolData &MSD,
+                   const MCAsmLayout &Layout);
+
+  void reportInvalidSize(MCAssembler &Asm, const MCAsmLayout &Layout,
+                         const MCExpr *SizeExpr);
 
   // Start and end offset of each section
   using SectionOffsetsTy =
@@ -519,8 +525,9 @@
   return true;
 }
 
-void ELFWriter::writeSymbol(SymbolTableWriter &Writer, uint32_t StringIndex,
-                            ELFSymbolData &MSD, const MCAsmLayout &Layout) {
+void ELFWriter::writeSymbol(MCAssembler &Asm, SymbolTableWriter &Writer,
+                            uint32_t StringIndex, ELFSymbolData &MSD,
+                            const MCAsmLayout &Layout) {
   const auto &Symbol = cast<MCSymbolELF>(*MSD.Symbol);
   const MCSymbolELF *Base =
       cast_or_null<MCSymbolELF>(Layout.getBaseSymbol(Symbol));
@@ -553,8 +560,10 @@
 
   if (ESize) {
     int64_t Res;
-    if (!ESize->evaluateKnownAbsolute(Res, Layout))
-      report_fatal_error("Size expression must be absolute.");
+    if (!ESize->evaluateKnownAbsolute(Res, Layout)) {
+      reportInvalidSize(Asm, Layout, ESize);
+      return;
+    }
     Size = Res;
   }
 
@@ -563,6 +572,55 @@
                      IsReserved);
 }
 
+void ELFWriter::reportInvalidSize(MCAssembler &Asm, const MCAsmLayout &Layout,
+                                  const MCExpr *SizeExpr) {
+  MCContext &Ctx = Asm.getContext();
+  SMLoc SizeLoc = SizeExpr->getLoc();
+  Ctx.reportError(SizeLoc, "size expression is not absolute");
+  const SourceMgr *SM = Ctx.getSourceManager();
+
+  if (!SM)
+    return;
+
+  auto NoteNotInSect = [&SM, &SizeLoc](MCSymbol const &SymRef) {
+    SM->PrintMessage(SizeLoc, SourceMgr::DK_Note,
+                     Twine("symbol '") + SymRef.getName() +
+                         "' is not defined in this section");
+  };
+  auto NoteUndef = [&SM, &Asm](MCSymbol const &SymRef, SMLoc Loc) {
+    SM->PrintMessage(Loc, SourceMgr::DK_Note, "symbol not defined");
+
+    const unsigned MaxEditDist = 2;
+    for (const MCSymbol &Sym : Asm.symbols()) {
+      StringRef Name = Sym.getName();
+      if (Name.edit_distance(SymRef.getName()) < MaxEditDist)
+        SM->PrintMessage(Loc, SourceMgr::DK_Note,
+                         Twine("did you mean to refer to '") + Name +
+                             Twine("'?"));
+    }
+  };
+  auto NoteSym = [=](MCSymbol const &Sym, SMLoc Loc) {
+    if (Sym.isUndefined())
+      NoteUndef(Sym, Loc);
+    else if (Sym.isInSection() && !Sym.getName().empty())
+      NoteNotInSect(Sym);
+  };
+
+  if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(SizeExpr)) {
+    NoteSym(Ref->getSymbol(), Ref->getLoc());
+  } else if (SizeExpr->getKind() == MCExpr::Binary) {
+    const MCBinaryExpr *BE = static_cast<const MCBinaryExpr *>(SizeExpr);
+    MCValue V;
+
+    if (BE->evaluateAsRelocatable(V, &Layout, nullptr)) {
+      if (V.getSymA())
+        NoteSym(V.getSymA()->getSymbol(), V.getSymA()->getLoc());
+      if (V.getSymB())
+        NoteSym(V.getSymB()->getSymbol(), V.getSymB()->getLoc());
+    }
+  }
+}
+
 bool ELFWriter::isInSymtab(const MCAsmLayout &Layout, const MCSymbolELF &Symbol,
                            bool Used, bool Renamed) {
   if (Symbol.isVariable()) {
@@ -736,7 +794,7 @@
                                ? 0
                                : StrTabBuilder.getOffset(MSD.Name);
     MSD.Symbol->setIndex(Index++);
-    writeSymbol(Writer, StringIndex, MSD, Layout);
+    writeSymbol(Asm, Writer, StringIndex, MSD, Layout);
   }
   for (; FileNameIt != FileNames.end(); ++FileNameIt) {
     Writer.writeSymbol(StrTabBuilder.getOffset(FileNameIt->first),
@@ -751,7 +809,7 @@
   for (ELFSymbolData &MSD : ExternalSymbolData) {
     unsigned StringIndex = StrTabBuilder.getOffset(MSD.Name);
     MSD.Symbol->setIndex(Index++);
-    writeSymbol(Writer, StringIndex, MSD, Layout);
+    writeSymbol(Asm, Writer, StringIndex, MSD, Layout);
     assert(MSD.Symbol->getBinding() != ELF::STB_LOCAL);
   }
 
diff --git a/llvm/test/MC/ELF/size-error.s b/llvm/test/MC/ELF/size-error.s
new file mode 100644
--- /dev/null
+++ b/llvm/test/MC/ELF/size-error.s
@@ -0,0 +1,35 @@
+// RUN: not llvm-mc -filetype=obj -triple x86_64-pc-linux < %s 2>&1 \
+// RUN: | FileCheck --implicit-check-not=error %s
+
+.section some
+
+Bar:
+nop
+
+.section other
+
+foo:
+	.size	foo, fo
+// CHECK: error: size expression is not absolute
+// CHECK: note: symbol not defined
+// CHECK: note: did you mean to refer to 'foo'?
+
+ethers:
+    nop
+	.size	ethers, Bar + 42
+// CHECK: error: size expression is not absolute
+// CHECK: note: symbol 'Bar' is not defined in this section
+
+a:
+	.size	a, . - others
+// CHECK: error: size expression is not absolute
+// CHECK: note: symbol not defined
+// CHECK: note: did you mean to refer to 'other'?
+// CHECK: note: did you mean to refer to 'ethers'?
+
+bar:
+	.size	bar, 31 - baz
+
+// CHECK: error: size expression is not absolute
+// CHECK: note: symbol not defined
+// CHECK: note: did you mean to refer to 'bar'?