Clear output section from linker script command when it's removed.

[dmikulin]

Summary

This is an attempt to fix https://bugs.llvm.org/show_bug.cgi?id=33029.
When output sections are removed, the need to be purged from linker script commands that define them.

[dmikulin]

Updated diff to address comments from the review and the online discussion.

[ruiu]

ELF/LinkerScript.cpp

703

What is the meaning of this change?

[dmikulin]

ELF/LinkerScript.cpp

703

Rafael suggested that we should not be tracking section types of previous sections and always use PROGBITS for dummy sections.

[dmikulin]

Removed Writer.cpp changes.

ELF/LinkerScript.h

struct ScriptConfiguration {
   llvm::DenseMap<llvm::StringRef, MemoryRegion> MemoryRegions;
 
   // A list of symbols referenced by the script.
   std::vector<llvm::StringRef> ReferencedSymbols;
 };
 
 class LinkerScript final {
   llvm::DenseMap<OutputSection *, OutputSectionCommand *> SecToCommand;
-  OutputSectionCommand *getCmd(OutputSection *Sec) const;
   void assignSymbol(SymbolAssignment *Cmd, bool InSec);
   void setDot(Expr E, const Twine &Loc, bool InSec);
 
   std::vector<InputSectionBase *>
   computeInputSections(const InputSectionDescription *);
 
   std::vector<InputSectionBase *>
   createInputSectionList(OutputSectionCommand &Cmd);
class LinkerScript final {
   uint64_t Dot;
   uint64_t ThreadBssOffset = 0;
 
   std::function<uint64_t()> LMAOffset;
   OutputSection *CurOutSec = nullptr;
   MemoryRegion *CurMemRegion = nullptr;
 
 public:
+  OutputSectionCommand *getCmd(OutputSection *Sec) const;
   bool hasPhdrsCommands() { return !Opt.PhdrsCommands.empty(); }
   uint64_t getDot() { return Dot; }
   OutputSection *getOutputSection(const Twine &Loc, StringRef S);
   uint64_t getOutputSectionSize(StringRef S);
   void discard(ArrayRef<InputSectionBase *> V);
 
   ExprValue getSymbolValue(const Twine &Loc, StringRef S);
   bool isDefined(StringRef S);

ELF/LinkerScript.cpp

 }
 
 void LinkerScript::adjustSectionsBeforeSorting() {
   // If the output section contains only symbol assignments, create a
   // corresponding output section. The bfd linker seems to only create them if
   // '.' is assigned to, but creating these section should not have any bad
   // consequeces and gives us a section to put the symbol in.
   uint64_t Flags = SHF_ALLOC;
-  uint32_t Type = SHT_PROGBITS;
 
   for (int I = 0, E = Opt.Commands.size(); I != E; ++I) {
     auto *Cmd = dyn_cast<OutputSectionCommand>(Opt.Commands[I]);
     if (!Cmd)
       continue;
     if (OutputSection *Sec = Cmd->Sec) {
       Flags = Sec->Flags;
-      Type = Sec->Type;
       continue;
     }
 
     if (isAllSectionDescription(*Cmd))
       continue;
 
-    auto *OutSec = make<OutputSection>(Cmd->Name, Type, Flags);
+    auto *OutSec = make<OutputSection>(Cmd->Name, SHT_PROGBITS, Flags);
     OutSec->SectionIndex = I;
     OutputSections->push_back(OutSec);
     Cmd->Sec = OutSec;
     SecToCommand[OutSec] = Cmd;
   }
 }
 
 void LinkerScript::adjustSectionsAfterSorting() {

ELF/Writer.cpp

for (InputSectionBase *S : llvm::reverse(InputSections)) {
     if (!SS->empty() || !SS->OutSec)
       continue;
 
     SS->OutSec->Sections.erase(std::find(SS->OutSec->Sections.begin(),
                                          SS->OutSec->Sections.end(), SS));
     SS->Live = false;
     // If there are no other sections in the output section, remove it from the
     // output.
-    if (SS->OutSec->Sections.empty())
+    if (SS->OutSec->Sections.empty()) {
       V.erase(std::find(V.begin(), V.end(), SS->OutSec));
+      OutputSectionCommand *Cmd = Script->getCmd(SS->OutSec);
+      if (Cmd)
+        Cmd->Sec = nullptr;
+    }
   }
 }
 
 // Create output section objects and add them to OutputSections.
 template <class ELFT> void Writer<ELFT>::finalizeSections() {
   Out::DebugInfo = findSection(".debug_info");
   Out::PreinitArray = findSection(".preinit_array");
   Out::InitArray = findSection(".init_array");

test/ELF/linkerscript/arm-lscript.s

+// REQUIRES: arm
+// RUN: llvm-mc -filetype=obj -triple=armv7a-none-linux-gnueabi %s -o %t.o
+// RUN: echo  "SECTIONS { \
+// RUN:         .rel.dyn : {    } \
+// RUN:         .zed     : { PROVIDE_HIDDEN (foobar = .); } \
+// RUN:         }" > %t.script
+// This is a test case for PR33029. Making sure that linker can digest
+// the above script without dumping core.
+// RUN: ld.lld -emit-relocs -T %t.script %t.o -shared -o %t.so