From da5cc8466186b15f31db3c7c98c4f0eee3ad7ced Mon Sep 17 00:00:00 2001
From: Rui Ueyama <ruiu@google.com>
Date: Thu, 16 Feb 2017 04:12:19 +0000
Subject: [PATCH] Add CopyRelSection instances to BSS in the regular way.

Previously, space in a BSS section for copy relocations are reserved
in a special way. We directly manipulated size of the BSS section.
r294577 changed the way of doing it. Now, we create an instance of
CopyRelSection (which is a synthetic input section) for each copy
relocation.

This patch removes the remains of the old way and add CopyRelSections
to BSS sections using `addSections` function, which is the usual
way to add an input section to an output section.

llvm-svn: 295278
---
 lld/ELF/Relocations.cpp     | 25 ++++++++-----------------
 lld/ELF/SyntheticSections.h |  3 ++-
 lld/ELF/Writer.cpp          | 14 +++++++++-----
 3 files changed, 19 insertions(+), 23 deletions(-)

diff --git a/lld/ELF/Relocations.cpp b/lld/ELF/Relocations.cpp
index 57ff259141c3..9e0f46291857 100644
--- a/lld/ELF/Relocations.cpp
+++ b/lld/ELF/Relocations.cpp
@@ -426,37 +426,28 @@ template <class ELFT> static void addCopyRelSymbol(SharedSymbol<ELFT> *SS) {
   // See if this symbol is in a read-only segment. If so, preserve the symbol's
   // memory protection by reserving space in the .bss.rel.ro section.
   bool IsReadOnly = isReadOnly(SS);
-  OutputSection<ELFT> *CopySec =
-      IsReadOnly ? Out<ELFT>::BssRelRo : Out<ELFT>::Bss;
+  OutputSection<ELFT> *OSec = IsReadOnly ? Out<ELFT>::BssRelRo : Out<ELFT>::Bss;
 
-  uintX_t Alignment = getAlignment(SS);
-  uintX_t Off = alignTo(CopySec->Size, Alignment);
-  CopySec->Size = Off + SymSize;
-  CopySec->updateAlignment(Alignment);
-  uintX_t Shndx = SS->Sym.st_shndx;
-  uintX_t Value = SS->Sym.st_value;
-
-  // Create a SyntheticSection in CopySec to hold the .bss and the Copy Reloc
-  auto *CopyISec = make<CopyRelSection<ELFT>>(IsReadOnly, Alignment, SymSize);
-  CopyISec->OutSecOff = Off;
-  CopyISec->OutSec = CopySec;
-  CopySec->Sections.push_back(CopyISec);
+  // Create a SyntheticSection in Out to hold the .bss and the Copy Reloc.
+  auto *ISec =
+      make<CopyRelSection<ELFT>>(IsReadOnly, getAlignment(SS), SymSize);
+  OSec->addSection(ISec);
 
   // Look through the DSO's dynamic symbol table for aliases and create a
   // dynamic symbol for each one. This causes the copy relocation to correctly
   // interpose any aliases.
   for (const Elf_Sym &S : SS->file()->getGlobalSymbols()) {
-    if (S.st_shndx != Shndx || S.st_value != Value)
+    if (S.st_shndx != SS->Sym.st_shndx || S.st_value != SS->Sym.st_value)
       continue;
     auto *Alias = dyn_cast_or_null<SharedSymbol<ELFT>>(
         Symtab<ELFT>::X->find(check(S.getName(SS->file()->getStringTable()))));
     if (!Alias)
       continue;
-    Alias->CopySection = CopyISec;
+    Alias->CopySection = ISec;
     Alias->NeedsCopyOrPltAddr = true;
     Alias->symbol()->IsUsedInRegularObj = true;
   }
-  In<ELFT>::RelaDyn->addReloc({Target->CopyRel, CopyISec, 0, false, SS, 0});
+  In<ELFT>::RelaDyn->addReloc({Target->CopyRel, ISec, 0, false, SS, 0});
 }
 
 template <class ELFT>
diff --git a/lld/ELF/SyntheticSections.h b/lld/ELF/SyntheticSections.h
index 3af25a57353e..a1190d2803f4 100644
--- a/lld/ELF/SyntheticSections.h
+++ b/lld/ELF/SyntheticSections.h
@@ -107,7 +107,8 @@ private:
   uint8_t *HashBuf;
 };
 
-// SHT_NOBITS section created for a copyReloc
+// For each copy relocation, we create an instance of this class to
+// reserve space in .bss or .bss.rel.ro.
 template <class ELFT>
 class CopyRelSection final : public SyntheticSection<ELFT> {
   typedef typename ELFT::uint uintX_t;
diff --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp
index 5ec87dc425cf..9a1741f3a043 100644
--- a/lld/ELF/Writer.cpp
+++ b/lld/ELF/Writer.cpp
@@ -1184,12 +1184,16 @@ template <class ELFT> void Writer<ELFT>::finalizeSections() {
 }
 
 template <class ELFT> void Writer<ELFT>::addPredefinedSections() {
-  if (Out<ELFT>::Bss->Size > 0)
-    OutputSections.push_back(Out<ELFT>::Bss);
-  if (Out<ELFT>::BssRelRo->Size > 0)
-    OutputSections.push_back(Out<ELFT>::BssRelRo);
+  auto Add = [=](OutputSection<ELFT> *Sec) {
+    if (!Sec->Sections.empty()) {
+      Sec->assignOffsets();
+      OutputSections.push_back(Sec);
+    }
+  };
+  Add(Out<ELFT>::Bss);
+  Add(Out<ELFT>::BssRelRo);
 
-  auto OS = dyn_cast_or_null<OutputSection<ELFT>>(findSection(".ARM.exidx"));
+  auto *OS = dyn_cast_or_null<OutputSection<ELFT>>(findSection(".ARM.exidx"));
   if (OS && !OS->Sections.empty() && !Config->Relocatable)
     OS->addSection(make<ARMExidxSentinelSection<ELFT>>());
 }