[lld][linkerscript] Fix handling of DEFINED.

[abidh]

Summary

Current implementation did not check that symbols is actually defined. Only checked for presence. GNU ld documentation says,

"Return 1 if symbol is in the linker global symbol table and is defined before the statement using DEFINED in the script, otherwise return 0."

https://sourceware.org/binutils/docs/ld/Builtin-Functions.html#Builtin-Functions

[MaskRay]

This is correct, however, can you just add a test to linkerscript/defined.test?

[abidh]

Moved test to linkerscript/define.test as advised.

[MaskRay]

Looks great!

lld/ELF/ScriptParser.cpp

if (tok == "DATA_SEGMENT_RELRO_END") {
     expect(",");
     readExpr();
     expect(")");
     Expr e = getPageSize();
     return [=] { return alignTo(script->getDot(), e().getValue()); };
   }
   if (tok == "DEFINED") {
     StringRef name = readParenLiteral();
-    return [=] { return symtab->find(name) ? 1 : 0; };
+    return [=] {
+      Symbol *b = symtab->find(name);
+      return (b && b->isDefined()) ? 1 : 0;
+    };
   }
   if (tok == "LENGTH") {
     StringRef name = readParenLiteral();
     if (script->memoryRegions.count(name) == 0) {
       setError("memory region not defined: " + name);
       return [] { return 0; };
     }
     return script->memoryRegions[name]->length;

lld/test/ELF/linkerscript/Inputs/define.s

 .global defined
 defined = 0
 
 .section .foo,"a"
 .quad 1
 
 .section .bar,"a"
 .quad 1
+
+.section .test,"a"
+.quad 1

lld/test/ELF/linkerscript/define.test

 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %p/Inputs/define.s -o %t.o
 # RUN: ld.lld -o %t --script %s %t.o
 # RUN: llvm-objdump --section-headers %t | FileCheck %s
 
+EXTERN(extern_defined)
 SECTIONS {
   . = DEFINED(defined) ? 0x11000 : .;
   .foo : { *(.foo*) }
   . = DEFINED(notdefined) ? 0x12000 : 0x13000;
   .bar : { *(.bar*) }
+  . = DEFINED(extern_defined) ? 0x14000 : 0x15000;
+  .test : { *(.test*) }
 }
 
 # CHECK: 1 .foo  00000008 0000000000011000 DATA
 # CHECK: 2 .bar  00000008 0000000000013000 DATA
-# CHECK: 3 .text 00000000 0000000000013008 TEXT
+# CHECK: 3 .test  00000008 0000000000015000 DATA
+# CHECK: 4 .text 00000000 0000000000015008 TEXT