[ELF/Linkerscript] Define an absolute if we find an undefined.

Otherwhise undefined references to symbols defined in linker scripts
are never resolved.

Differential Revision:  https://reviews.llvm.org/D22664

llvm-svn: 276536

lld/ELF/LinkerScript.cpp

@@ -532,7 +532,8 @@ template <class ELFT> void LinkerScript<ELFT>::addScriptedSymbols() {
     if (!Cmd || Cmd->Name == ".")
       continue;
 
-    if (Symtab<ELFT>::X->find(Cmd->Name) == nullptr)
+    SymbolBody *B = Symtab<ELFT>::X->find(Cmd->Name);
+    if (!B || B->isUndefined())
       Symtab<ELFT>::X->addAbsolute(Cmd->Name,
                                    Cmd->Hidden ? STV_HIDDEN : STV_DEFAULT);
     else

lld/test/ELF/linkerscript-undef.s

@@ -0,0 +1,11 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+
+# RUN: echo "SECTIONS { patatino = 0x1234; }" > %t.script
+# RUN: ld.lld -o %t1 --script %t.script %t
+# RUN: llvm-objdump -t %t1 | FileCheck %s
+# CHECK: 0000000000001234         *ABS*    00000000 patatino
+
+.global _start
+_start:
+  call patatino