[ELF] implement --warn-common/--no-warn-common

-warn-common
Warn when a common symbol is combined with another common symbol
or with a symbol definition.  Unix linkers allow  this  somewhat
sloppy  practice, but linkers on some other operating systems do
not.  This option allows you to  find  potential  problems  from
combining global symbols.

Differential revision: http://reviews.llvm.org/D17998

llvm-svn: 263413

lld/ELF/Config.h

@@ -78,6 +78,7 @@ struct Configuration {
   bool SysvHash = true;
   bool Threads;
   bool Verbose;
+  bool WarnCommon;
   bool ZExecStack;
   bool ZNodelete;
   bool ZNow;

lld/ELF/Driver.cpp

@@ -244,6 +244,7 @@ void LinkerDriver::readConfigs(opt::InputArgList &Args) {
   Config->StripAll = Args.hasArg(OPT_strip_all);
   Config->Threads = Args.hasArg(OPT_threads);
   Config->Verbose = Args.hasArg(OPT_verbose);
+  Config->WarnCommon = Args.hasArg(OPT_warn_common);
 
   Config->DynamicLinker = getString(Args, OPT_dynamic_linker);
   Config->Entry = getString(Args, OPT_entry);

lld/ELF/Options.td

@@ -131,6 +131,9 @@ def verbose : Flag<["--"], "verbose">;
 def version : Flag<["--", "-"], "version">,
   HelpText<"Display the version number">;
 
+def warn_common : Flag<["--", "-"], "warn-common">,
+  HelpText<"Warn about duplicate common symbols">;
+
 def whole_archive : Flag<["--", "-"], "whole-archive">,
   HelpText<"Force load of all members in a static library">;
 
@@ -178,9 +181,9 @@ def start_group_paren: Flag<["-"], "(">;
 def fatal_warnings : Flag<["--"], "fatal-warnings">;
 def no_add_needed : Flag<["--"], "no-add-needed">;
 def no_fatal_warnings : Flag<["--"], "no-fatal-warnings">;
+def no_warn_common : Flag<["--", "-"], "no-warn-common">;
 def no_warn_mismatch : Flag<["--"], "no-warn-mismatch">;
 def version_script : Separate<["--"], "version-script">;
-def warn_common : Flag<["--"], "warn-common">;
 def warn_shared_textrel : Flag<["--"], "warn-shared-textrel">;
 def G : Separate<["-"], "G">;
 

lld/ELF/Symbols.cpp

@@ -159,6 +159,8 @@ static uint8_t getMinVisibility(uint8_t VA, uint8_t VB) {
 }
 
 static int compareCommons(DefinedCommon *A, DefinedCommon *B) {
+  if (Config->WarnCommon)
+    warning("multiple common of " + A->getName());
   A->Alignment = B->Alignment = std::max(A->Alignment, B->Alignment);
   if (A->Size < B->Size)
     return -1;
@@ -199,6 +201,8 @@ template <class ELFT> int SymbolBody::compare(SymbolBody *Other) {
   if (isCommon() && Other->isCommon())
     return compareCommons(cast<DefinedCommon>(this),
                           cast<DefinedCommon>(Other));
+  if (Config->WarnCommon)
+    warning("common " + this->getName() + " is overridden");
   return isCommon() ? -1 : 1;
 }
 

lld/test/ELF/Inputs/warn-common.s

@@ -0,0 +1,2 @@
+.type arr,@object
+.comm arr,8,4

lld/test/ELF/Inputs/warn-common2.s

@@ -0,0 +1,8 @@
+.type arr,@object
+.data
+.globl arr
+.p2align 2
+arr:
+ .long 1
+ .long 0
+ .size arr, 8

lld/test/ELF/warn-common.s

@@ -0,0 +1,25 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t1.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %p/Inputs/warn-common.s -o %t2.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %p/Inputs/warn-common2.s -o %t3.o
+
+## Report multiple commons if warn-common is specified
+# RUN: ld.lld --warn-common %t1.o %t2.o -o %t.out 2>&1 | FileCheck %s --check-prefix=WARN
+# WARN: multiple common of arr
+
+## no-warn-common is ignored
+# RUN: ld.lld --no-warn-common %t1.o %t2.o -o %t.out
+# RUN: llvm-readobj %t.out > /dev/null
+
+## Report if common is overridden
+# RUN: ld.lld --warn-common %t1.o %t3.o -o %t.out 2>&1 | FileCheck %s --check-prefix=OVER
+# OVER: common arr is overridden
+
+## Report if common is overridden, but in different order
+# RUN: ld.lld --warn-common %t3.o %t1.o -o %t.out 2>&1 | FileCheck %s --check-prefix=OVER
+
+.globl _start
+_start:
+
+.type arr,@object
+.comm arr,4,4