[ELF] Ensure output section is not discarded in addStartEndSymbols()

Fixes https://bugs.llvm.org/show_bug.cgi?id=52534.

Differential Revision: https://reviews.llvm.org/D114179

Author: nga888

lld/ELF/LinkerScript.cpp

@@ -1034,7 +1034,7 @@ void LinkerScript::assignOffsets(OutputSection *sec) {
   }
 }
 
-static bool isDiscardable(OutputSection &sec) {
+static bool isDiscardable(const OutputSection &sec) {
   if (sec.name == "/DISCARD/")
     return true;
 
@@ -1063,6 +1063,11 @@ static bool isDiscardable(OutputSection &sec) {
   return true;
 }
 
+bool LinkerScript::isDiscarded(const OutputSection *sec) const {
+  return hasSectionsCommand && (getFirstInputSection(sec) == nullptr) &&
+         isDiscardable(*sec);
+}
+
 static void maybePropagatePhdrs(OutputSection &sec,
                                 std::vector<StringRef> &phdrs) {
   if (sec.phdrs.empty()) {

lld/ELF/LinkerScript.h

@@ -318,6 +318,8 @@ class LinkerScript final {
   void processSymbolAssignments();
   void declareSymbols();
 
+  bool isDiscarded(const OutputSection *sec) const;
+
   // Used to handle INSERT AFTER statements.
   void processInsertCommands();
 

lld/ELF/Writer.cpp

@@ -2276,7 +2276,7 @@ template <class ELFT> void Writer<ELFT>::addStartEndSymbols() {
     Default = Out::elfHeader;
 
   auto define = [=](StringRef start, StringRef end, OutputSection *os) {
-    if (os) {
+    if (os && !script->isDiscarded(os)) {
       addOptionalRegular(start, os, 0);
       addOptionalRegular(end, os, -1);
     } else {

lld/test/ELF/linkerscript/preinit-array-empty.test

@@ -0,0 +1,39 @@
+# REQUIRES: x86
+# RUN: split-file %s %t
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/t.s -o %t.o
+
+## PR52534: https://bugs.llvm.org/show_bug.cgi?id=52534
+## Check case where .preinit_array is discarded.
+## Link should succeed without causing an out of range relocation error.
+# RUN: ld.lld -T %t/discarded.script %t.o -o %t1 --image-base=0x80000000
+# RUN: llvm-readelf -s %t1 | FileCheck --check-prefixes=CHECK,DISCARDED %s
+
+## Check case where .preinit_array is emitted but empty.
+# RUN: ld.lld -T %t/empty.script %t.o -o %t2
+# RUN: llvm-readelf -s %t2 | FileCheck --check-prefixes=CHECK,EMPTY %s
+
+# CHECK:          [[#%x,ADDR:]] 0 NOTYPE  LOCAL  HIDDEN      [[#]] __preinit_array_start
+# CHECK-NEXT:     [[#ADDR]]     0 NOTYPE  LOCAL  HIDDEN      [[#]] __preinit_array_end
+
+# DISCARDED-NEXT: [[#ADDR]]     0 NOTYPE  GLOBAL DEFAULT     [[#]] _start
+
+# EMPTY-NOT:      [[#ADDR]]     0 NOTYPE  GLOBAL DEFAULT     [[#]] _start
+# EMPTY:          [[#ADDR]]     0 NOTYPE  GLOBAL DEFAULT     [[#]] ADDR
+
+#--- t.s
+.global _start
+_start:
+ movq __preinit_array_start@GOTPCREL(%rip),%rax
+ movq __preinit_array_end@GOTPCREL(%rip),%rax
+
+#--- discarded.script
+SECTIONS {
+  .text : { *(.text); }
+  .preinit_array : { *(.preinit_array); }
+}
+
+#--- empty.script
+SECTIONS {
+  .text : { *(.text); }
+  .preinit_array : { ADDR = .; *(.preinit_array); }
+}