Handle copy relocations in symbol assignments.

When a linker script has "foo = bar" and bar is the result of a copy
relocation foo should point to the same location in .bss.

This is part of a growing evidence that copy relocations should be
implemented by using replaceSymbol to replace the SharedSymbol with a
Defined.

llvm-svn: 319449

lld/ELF/LinkerScript.cpp

@@ -976,8 +976,13 @@ ExprValue LinkerScript::getSymbolValue(StringRef Name, const Twine &Loc) {
     return 0;
   }
 
-  if (auto *Sym = dyn_cast_or_null<Defined>(Symtab->find(Name)))
+  if (Symbol *Sym = Symtab->find(Name)) {
-    return {Sym->Section, false, Sym->Value, Loc};
+    if (auto *DS = dyn_cast<Defined>(Sym))
+      return {DS->Section, false, DS->Value, Loc};
+    if (auto *SS = dyn_cast<SharedSymbol>(Sym))
+      if (!ErrorOnMissingSection || SS->CopyRelSec)
+        return {SS->CopyRelSec, false, 0, Loc};
+  }
 
   error(Loc + ": symbol not found: " + Name);
   return 0;

lld/test/ELF/linkerscript/Inputs/copy-rel-symbol-value.s

@@ -0,0 +1,5 @@
+        .global bar
+        .type bar, @object
+        .size bar, 8
+bar:
+        .quad 0

lld/test/ELF/linkerscript/copy-rel-symbol-value-err.s

@@ -0,0 +1,12 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %p/Inputs/copy-rel-symbol-value.s -o %t2.o
+# RUN: ld.lld %t2.o -o %t2.so -shared
+# RUN: echo "SECTIONS { . = . + SIZEOF_HEADERS; foo = bar; }" > %t.script
+# RUN: not ld.lld %t.o %t2.so --script %t.script -o %t 2>&1 | FileCheck %s
+
+# CHECK: symbol not found: bar
+
+.global _start
+_start:
+.quad bar@got

lld/test/ELF/linkerscript/copy-rel-symbol-value.s

@@ -0,0 +1,27 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %p/Inputs/copy-rel-symbol-value.s -o %t2.o
+# RUN: ld.lld %t2.o -o %t2.so -shared
+# RUN: echo "SECTIONS { . = . + SIZEOF_HEADERS; foo = bar; }" > %t.script
+# RUN: ld.lld %t.o %t2.so --script %t.script -o %t
+# RUN: llvm-readobj -t %t | FileCheck %s
+
+# CHECK:      Name: bar
+# CHECK-NEXT: Value: 0x[[VAL:.*]]
+# CHECK-NEXT: Size: 8
+# CHECK-NEXT: Binding: Global
+# CHECK-NEXT: Type: Object
+# CHECK-NEXT: Other: 0
+# CHECK-NEXT: Section: .bss.rel.ro
+
+# CHECK:      Name: foo
+# CHECK-NEXT: Value: 0x[[VAL]]
+# CHECK-NEXT: Size:
+# CHECK-NEXT: Binding: Global
+# CHECK-NEXT: Type:
+# CHECK-NEXT: Other: 0
+# CHECK-NEXT: Section: .bss.rel.ro
+
+.global _start
+_start:
+.quad bar