[lld] r370437 - [ELF] Set `referenced` bit of Undefined created by BitcodeFile

[Fangrui Song via llvm-commits]

Author: maskray
Date: Fri Aug 30 00:10:30 2019
New Revision: 370437

URL: http://llvm.org/viewvc/llvm-project?rev=370437&view=rev
Log:
[ELF] Set `referenced` bit of Undefined created by BitcodeFile

D64136 and D65584, while fixing STB_WEAK issues and improving our
compatibility with ld.bfd, can cause another STB_WEAK problem related to
LTO:

If %tundef.o has an undefined reference on f,
and %tweakundef.o has a weak undefined reference on f,
%tdef.o has a definition of f

```
ld.lld %tundef.o %tweakundef.o --start-lib %tdef.o --end-lib
```

1) `%tundef.o` doesn't set the `referenced` bit.
2) `%weakundef.o` changes the binding from STB_GLOBAL to STB_WEAK
3) `%tdef.o` is not fetched because the binding is weak.

Step (1) is incorrect. This patch sets the `referenced` bit of Undefined
created by bitcode files.

Reviewed By: ruiu

Differential Revision: https://reviews.llvm.org/D66992

Added:
    lld/trunk/test/ELF/lto/Inputs/undef.ll
    lld/trunk/test/ELF/lto/undef-weak-lazy.ll
Modified:
    lld/trunk/ELF/InputFiles.cpp

Modified: lld/trunk/ELF/InputFiles.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/InputFiles.cpp?rev=370437&r1=370436&r2=370437&view=diff
==============================================================================
--- lld/trunk/ELF/InputFiles.cpp (original)
+++ lld/trunk/ELF/InputFiles.cpp Fri Aug 30 00:10:30 2019
@@ -1478,7 +1478,9 @@ static Symbol *createBitcodeSymbol(const
     Undefined newSym(&f, name, binding, visibility, type);
     if (canOmitFromDynSym)
       newSym.exportDynamic = false;
-    return symtab->addSymbol(newSym);
+    Symbol *ret = symtab->addSymbol(newSym);
+    ret->referenced = true;
+    return ret;
   }
 
   if (objSym.isCommon())

Added: lld/trunk/test/ELF/lto/Inputs/undef.ll
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/lto/Inputs/undef.ll?rev=370437&view=auto
==============================================================================
--- lld/trunk/test/ELF/lto/Inputs/undef.ll (added)
+++ lld/trunk/test/ELF/lto/Inputs/undef.ll Fri Aug 30 00:10:30 2019
@@ -0,0 +1,4 @@
+target triple = "x86_64-unknown-linux-gnu"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+declare void @foo()

Added: lld/trunk/test/ELF/lto/undef-weak-lazy.ll
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/lto/undef-weak-lazy.ll?rev=370437&view=auto
==============================================================================
--- lld/trunk/test/ELF/lto/undef-weak-lazy.ll (added)
+++ lld/trunk/test/ELF/lto/undef-weak-lazy.ll Fri Aug 30 00:10:30 2019
@@ -0,0 +1,23 @@
+; REQUIRES: x86
+; RUN: llvm-as %S/Inputs/undef.ll -o %tundef.o
+; RUN: llvm-as %s -o %tweakundef.o
+; RUN: llvm-as %S/Inputs/archive-3.ll -o %tdef.o
+
+;; Test that the lazy bitcode %tdef.o is fetched.
+; RUN: ld.lld %tundef.o --start-lib %tdef.o --end-lib -shared -o %t.so
+; RUN: llvm-nm %t.so | FileCheck %s
+
+;; Test %tweakundef.o does not change STB_GLOBAL to STB_WEAK.
+; RUN: ld.lld %tundef.o %tweakundef.o --start-lib %tdef.o --end-lib -shared -o %t.so
+; RUN: llvm-nm %t.so | FileCheck %s
+
+;; %tweakundef.o does not fetch %tdef.o but %tundef.o does.
+; RUN: ld.lld --start-lib %tdef.o --end-lib %tweakundef.o %tundef.o -shared -o %t.so
+; RUN: llvm-nm %t.so | FileCheck %s
+
+; CHECK: T foo
+
+target triple = "x86_64-unknown-linux-gnu"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+declare extern_weak void @foo()