[ELF] - Allow section to have multiple dependent sections.

That fixes a case when section has more than one metadata 
section. Previously GC would collect one of such sections 
because we had implementation that stored only last one as
dependent.

Differential revision: https://reviews.llvm.org/D29981

llvm-svn: 295298

lld/ELF/InputFiles.cpp

@@ -323,7 +323,7 @@ void elf::ObjectFile<ELFT>::initializeSections(
         fatal(toString(this) + ": invalid sh_link index: " +
               Twine(Sec.sh_link));
       auto *IS = cast<InputSection<ELFT>>(Sections[Sec.sh_link]);
-      IS->DependentSection = Sections[I];
+      IS->DependentSections.push_back(Sections[I]);
     }
   }
 }

lld/ELF/InputSection.h

@@ -281,8 +281,8 @@ public:
   // to. The writer sets a value.
   uint64_t OutSecOff = 0;
 
-  // InputSection that is dependent on us (reverse dependency for GC)
-  InputSectionBase<ELFT> *DependentSection = nullptr;
+  // InputSections that are dependent on us (reverse dependency for GC)
+  llvm::TinyPtrVector<InputSectionBase<ELFT> *> DependentSections;
 
   static bool classof(const InputSectionData *S);
 

lld/ELF/MarkLive.cpp

@@ -87,8 +87,8 @@ static void forEachSuccessor(InputSection<ELFT> &Sec,
     for (const typename ELFT::Rel &Rel : Sec.rels())
       Fn(resolveReloc(Sec, Rel));
   }
-  if (Sec.DependentSection)
-    Fn({Sec.DependentSection, 0});
+  for (InputSectionBase<ELFT> *IS : Sec.DependentSections)
+    Fn({IS, 0});
 }
 
 // The .eh_frame section is an unfortunate special case.

lld/test/ELF/gc-sections-metadata2.s

@@ -0,0 +1,19 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
+# RUN: ld.lld --gc-sections %t.o -o %t
+# RUN: llvm-objdump -section-headers %t | FileCheck %s
+
+# CHECK: .foo
+# CHECK: .bar
+# CHECK: .zed
+
+.globl _start
+_start:
+.quad .foo
+
+.section .foo,"a"
+.quad 0
+.section .bar,"am",@progbits,.foo
+.quad 0
+.section .zed,"am",@progbits,.foo
+.quad 0