From a7e4c407add2f5763a86680685541888a828cd37 Mon Sep 17 00:00:00 2001
From: Rafael Espindola <rafael.espindola@gmail.com>
Date: Mon, 19 Jan 2015 17:30:24 +0000
Subject: [PATCH] Produce errors when an assignment expression would use a
 common symbol.

An assignment will produce a symbol with a given section and offset. There is
no way to represent something like "1 byte after a common symbol".

This matches the behavior of GNU as.

Part of PR22217.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226470 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/MC/MCAssembler.cpp      | 12 +++++++++++-
 test/MC/ELF/common-error1.s |  6 ++++++
 test/MC/ELF/common-error2.s |  6 ++++++
 3 files changed, 23 insertions(+), 1 deletion(-)
 create mode 100644 test/MC/ELF/common-error1.s
 create mode 100644 test/MC/ELF/common-error2.s

diff --git a/lib/MC/MCAssembler.cpp b/lib/MC/MCAssembler.cpp
index e3c2443f4a2..b5b72827299 100644
--- a/lib/MC/MCAssembler.cpp
+++ b/lib/MC/MCAssembler.cpp
@@ -201,7 +201,17 @@ const MCSymbol *MCAsmLayout::getBaseSymbol(const MCSymbol &Symbol) const {
   if (!A)
     return nullptr;
 
-  return &A->getSymbol();
+  const MCSymbol &ASym = A->getSymbol();
+  const MCAssembler &Asm = getAssembler();
+  const MCSymbolData &ASD = Asm.getSymbolData(ASym);
+  if (ASD.isCommon()) {
+    // FIXME: we should probably add a SMLoc to MCExpr.
+    Asm.getContext().FatalError(SMLoc(),
+                                "Common symbol " + ASym.getName() +
+                                    " cannot be used in assignment expr");
+  }
+
+  return &ASym;
 }
 
 uint64_t MCAsmLayout::getSectionAddressSize(const MCSectionData *SD) const {
diff --git a/test/MC/ELF/common-error1.s b/test/MC/ELF/common-error1.s
new file mode 100644
index 00000000000..a413885b016
--- /dev/null
+++ b/test/MC/ELF/common-error1.s
@@ -0,0 +1,6 @@
+// RUN: not llvm-mc -filetype=obj -triple x86_64-pc-linux < %s 2>&1 | FileCheck %s
+
+        .comm   C,4,4
+        .set    A,C
+
+// CHECK: Common symbol C cannot be used in assignment expr
diff --git a/test/MC/ELF/common-error2.s b/test/MC/ELF/common-error2.s
new file mode 100644
index 00000000000..d666feedee6
--- /dev/null
+++ b/test/MC/ELF/common-error2.s
@@ -0,0 +1,6 @@
+// RUN: not llvm-mc -filetype=obj -triple x86_64-pc-linux < %s 2>&1 | FileCheck %s
+
+        .set    A,C
+        .comm   C,4,4
+
+// CHECK: Common symbol C cannot be used in assignment expr
-- 
2.34.1