[llvm-readobj][ELF] Show MIPS GOT content when there is another zero-sized section at the same address

[atanasyan]

Summary

It is possible to have .got section and one or more zero-sized section at the same address. This patch first checks that GOT (or GOT PLT) section should have non-zero size using corresponding dynamic tags. Then it looks up not empty section at the specified address.

[• rafael]

tools/llvm-readobj/ELFDumper.cpp

1889

This is a corrupted file and should be an error, no?

1966

This is also a corrupted file, no?

[atanasyan]

• Use report_fatal_error to show errors and exit with non-zero code

[• rafael]

lgtm

test/tools/llvm-readobj/mips-got-overlapped.test

+# Check that llvm-readobj -mips-plt-got correctly shows .got section
+# content if there are some other zero-sized sections with the same
+# address as the .got. got-over.exe.elf-mips has zero-sized .data
+# section at the same offset .got section.
+
+RUN: llvm-readobj -mips-plt-got %p/Inputs/got-over.exe.elf-mips | FileCheck %s
+
+GOT-OBJ: Cannot find PLTGOT dynamic table tag.
+
+CHECK:      Primary GOT {
+CHECK-NEXT:   Canonical gp value: 0x418270
+CHECK-NEXT:   Reserved entries [
+CHECK-NEXT:     Entry {
+CHECK-NEXT:       Address: 0x410280
+CHECK-NEXT:       Access: -32752
+CHECK-NEXT:       Initial: 0x0
+CHECK-NEXT:       Purpose: Lazy resolver
+CHECK-NEXT:     }
+CHECK-NEXT:     Entry {
+CHECK-NEXT:       Address: 0x410284
+CHECK-NEXT:       Access: -32748
+CHECK-NEXT:       Initial: 0x80000000
+CHECK-NEXT:       Purpose: Module pointer (GNU extension)
+CHECK-NEXT:     }
+CHECK-NEXT:   ]
+CHECK-NEXT:   Local entries [
+CHECK-NEXT:     Entry {
+CHECK-NEXT:       Address: 0x410288
+CHECK-NEXT:       Access: -32744
+CHECK-NEXT:       Initial: 0x4001B8
+CHECK-NEXT:     }
+CHECK-NEXT:   ]
+CHECK-NEXT:   Global entries [
+CHECK-NEXT:     Entry {
+CHECK-NEXT:       Address: 0x41028C
+CHECK-NEXT:       Access: -32740
+CHECK-NEXT:       Initial: 0x0
+CHECK-NEXT:       Value: 0x0
+CHECK-NEXT:       Type: None
+CHECK-NEXT:       Section: Undefined
+CHECK-NEXT:       Name: _foo
+CHECK-NEXT:     }
+CHECK-NEXT:   ]
+CHECK-NEXT:   Number of TLS and multi-GOT entries: 0
+CHECK-NEXT: }

tools/llvm-readobj/ELFDumper.cpp

if (SectionIndex == SHN_XINDEX)
           Obj.getExtendedSymbolTableIndex(Symbol, SymTab, ShndxTable);
     ErrorOr<const typename ELFO::Elf_Shdr *> Sec = Obj.getSection(SectionIndex);
     error(Sec.getError());
     SectionName = errorOrDefault(Obj.getSectionName(*Sec));
   }
 }
 
 template <class ELFO>
-static const typename ELFO::Elf_Shdr *findSectionByAddress(const ELFO *Obj,
-                                                           uint64_t Addr) {
+static const typename ELFO::Elf_Shdr *
+findNotEmptySectionByAddress(const ELFO *Obj, uint64_t Addr) {
   for (const auto &Shdr : Obj->sections())
-    if (Shdr.sh_addr == Addr)
+    if (Shdr.sh_addr == Addr && Shdr.sh_size > 0)
       return &Shdr;
   return nullptr;
 }
 
 template <class ELFO>
 static const typename ELFO::Elf_Shdr *findSectionByName(const ELFO &Obj,
                                                         StringRef Name) {
   for (const auto &Shdr : Obj.sections()) {
if (!DtLocalGotNum) {
     W.startLine() << "Cannot find MIPS_LOCAL_GOTNO dynamic table tag.\n";
     return;
   }
   if (!DtGotSym) {
     W.startLine() << "Cannot find MIPS_GOTSYM dynamic table tag.\n";
     return;
   }
 
-  const Elf_Shdr *GOTShdr = findSectionByAddress(Obj, *DtPltGot);
-  if (!GOTShdr) {
-    W.startLine() << "There is no .got section in the file.\n";
-    return;
-  }
-
-  ErrorOr<ArrayRef<uint8_t>> GOT = Obj->getSectionContents(GOTShdr);
-  if (!GOT) {
-    W.startLine() << "The .got section is empty.\n";
-    return;
-  }
-
-  if (*DtLocalGotNum > getGOTTotal(*GOT)) {
-    W.startLine() << "MIPS_LOCAL_GOTNO exceeds a number of GOT entries.\n";
-    return;
-  }
-
   const Elf_Shdr *DynSymSec = Dumper->getDotDynSymSec();
   ErrorOr<StringRef> StrTable = Obj->getStringTableForSymtab(*DynSymSec);
   error(StrTable.getError());
   const Elf_Sym *DynSymBegin = Obj->symbol_begin(DynSymSec);
   const Elf_Sym *DynSymEnd = Obj->symbol_end(DynSymSec);
   std::size_t DynSymTotal = std::size_t(std::distance(DynSymBegin, DynSymEnd));
 
   if (*DtGotSym > DynSymTotal) {
     W.startLine() << "MIPS_GOTSYM exceeds a number of dynamic symbols.\n";
     return;
   }
 
   std::size_t GlobalGotNum = DynSymTotal - *DtGotSym;
 
+  if (*DtLocalGotNum + GlobalGotNum == 0) {
+    W.startLine() << "GOT is empty.\n";
+    return;
+  }
+
+  const Elf_Shdr *GOTShdr = findNotEmptySectionByAddress(Obj, *DtPltGot);
+  if (!GOTShdr) {
+    W.startLine() << "There is no not empty GOT section at "
+                  << format("0x%" PRIX64, *DtPltGot) << ".\n ";
+    return;
+  }
+
+  ErrorOr<ArrayRef<uint8_t>> GOT = Obj->getSectionContents(GOTShdr);
+
   if (*DtLocalGotNum + GlobalGotNum > getGOTTotal(*GOT)) {
-    W.startLine() << "Number of global GOT entries exceeds the size of GOT.\n";
+    W.startLine() << "Number of GOT entries exceeds the size of GOT section.\n";
     return;
   }
 
   const GOTEntry *GotBegin = makeGOTIter(*GOT, 0);
   const GOTEntry *GotLocalEnd = makeGOTIter(*GOT, *DtLocalGotNum);
   const GOTEntry *It = GotBegin;
 
   DictScope GS(W, "Primary GOT");
if (!DtMipsPltGot) {
     W.startLine() << "Cannot find MIPS_PLTGOT dynamic table tag.\n";
     return;
   }
   if (!DtJmpRel) {
     W.startLine() << "Cannot find JMPREL dynamic table tag.\n";
     return;
   }
 
-  const Elf_Shdr *PLTShdr = findSectionByAddress(Obj, *DtMipsPltGot);
+  const Elf_Shdr *PLTShdr = findNotEmptySectionByAddress(Obj, *DtMipsPltGot);
   if (!PLTShdr) {
-    W.startLine() << "There is no .got.plt section in the file.\n";
+    W.startLine() << "There is no not empty PLTGOT section at "
+                  << format("0x%" PRIX64, *DtMipsPltGot) << ".\n";
     return;
   }
   ErrorOr<ArrayRef<uint8_t>> PLT = Obj->getSectionContents(PLTShdr);
-  if (!PLT) {
-    W.startLine() << "The .got.plt section is empty.\n";
-    return;
-  }
 
-  const Elf_Shdr *PLTRelShdr = findSectionByAddress(Obj, *DtJmpRel);
-  if (!PLTShdr) {
-    W.startLine() << "There is no .rel.plt section in the file.\n";
+  const Elf_Shdr *PLTRelShdr = findNotEmptySectionByAddress(Obj, *DtJmpRel);
+  if (!PLTRelShdr) {
+    W.startLine() << "There is no not empty RELPLT section at "
+                  << format("0x%" PRIX64, *DtJmpRel) << ".\n";
     return;
   }
   ErrorOr<const Elf_Shdr *> SymTableOrErr =
       Obj->getSection(PLTRelShdr->sh_link);
   error(SymTableOrErr.getError());
   const Elf_Shdr *SymTable = *SymTableOrErr;
   ErrorOr<StringRef> StrTable = Obj->getStringTableForSymtab(*SymTable);
   error(StrTable.getError());