Handle hits in PLT

AddressResolver.cpp

@@ -21,6 +21,8 @@ enum Section {
   DebugInfo,
   DebugLink,
   PrelinkUndo,
+  PLT,
+  RelPLT,
   SectionCount
 };
 
@@ -118,6 +120,7 @@ void ElfHolder::loadInfo()
     Elf_Scn* scn = elf_getscn(elf_, i);
     GElf_Shdr shdr;
     gelf_getshdr(scn, &shdr);
+    const char* sectionName;
 
     switch (shdr.sh_type)
     {
@@ -130,7 +133,7 @@ void ElfHolder::loadInfo()
       needToFind--;
       break;
     case SHT_PROGBITS:
-      const char* sectionName = elf_strptr(elf_, ehdr.e_shstrndx, shdr.sh_name);
+      sectionName = elf_strptr(elf_, ehdr.e_shstrndx, shdr.sh_name);
       if (strcmp(sectionName, ".debug_info") == 0)
       {
         sections_[DebugInfo] = scn;
@@ -146,23 +149,39 @@ void ElfHolder::loadInfo()
         sections_[PrelinkUndo] = scn;
         needToFind--;
       }
+      else if (strcmp(sectionName, ".plt") == 0)
+      {
+        sections_[PLT] = scn;
+        needToFind--;
+      }
+      break;
+    case SHT_REL:
+    case SHT_RELA:
+      sectionName = elf_strptr(elf_, ehdr.e_shstrndx, shdr.sh_name);
+      if (strcmp(sectionName, ".rel.plt") == 0 || strcmp(sectionName, "rela.plt"))
+      {
+        sections_[RelPLT] = scn;
+        needToFind--;
+      }
       break;
     }
   }
 }
 
 struct ARSymbolData
 {
+  enum { MiscPLT = 255 };
   explicit ARSymbolData(const GElf_Sym& elfSymbol)
     : size(elfSymbol.st_size)
-    , binding(GELF_ST_BIND(elfSymbol.st_info))
+    , misc(GELF_ST_BIND(elfSymbol.st_info))
   {}
   explicit ARSymbolData(uint64_t _size)
     : size(_size)
   {}
+  ARSymbolData() {}
   uint64_t size;
   std::string name;
-  unsigned char binding;
+  unsigned char misc;
 };
 
 typedef std::map<Range, ARSymbolData> ARSymbolStorage;
@@ -173,11 +192,13 @@ struct AddressResolverPrivate
   AddressResolverPrivate()
     : baseAddress(0)
     , origBaseAddress(0)
+    , pltEndAddress(0)
     , dwfl(0)
     , dwMod(0)
     , dwBias(0)
   {}
 
+  void loadPLTSymbols(Elf* elf, Elf_Scn* pltSection, Elf_Scn* relPltSection, Elf_Scn *dynsymSection);
   void loadSymbolsFromSection(Elf* elf, Elf_Scn* section);
   const char* getDebugLink(Elf_Scn* section);
   void setOriginalBaseAddress(Elf* elf, Elf_Scn* section);
@@ -186,6 +207,7 @@ struct AddressResolverPrivate
 
   uint64_t baseAddress;
   uint64_t origBaseAddress;
+  uint64_t pltEndAddress;
 
   Dwfl* dwfl;
   Dwfl_Module* dwMod;
@@ -209,6 +231,9 @@ AddressResolver::AddressResolver(Profile::DetailLevel details, const char *fileN
   ElfHolder elfh(fileName);
   d->origBaseAddress = d->baseAddress = elfh.getBaseAddress();
 
+  if (details != Profile::Objects && elfh.getSection(PLT) && elfh.getSection(RelPLT) && elfh.getSection(DynSym))
+    d->loadPLTSymbols(elfh.get(), elfh.getSection(PLT), elfh.getSection(RelPLT), elfh.getSection(DynSym));
+
   // Don't load symbols if not requested
   bool symTabLoaded = (details == Profile::Objects);
   // Try to load .symtab from main file
@@ -305,6 +330,9 @@ bool AddressResolver::resolve(Address value, Address loadBase, Range& symbolRang
     }
     else
       symbolName = maybeSymbolName;
+
+    if (arSymIt->second.misc == ARSymbolData::MiscPLT)
+      symbolName.append("@plt");
   }
 
   return true;
@@ -326,9 +354,57 @@ std::pair<const char*, size_t> AddressResolver::getSourcePosition(Address value,
   return std::make_pair(static_cast<const char*>(0), 0);
 }
 
+void AddressResolverPrivate::loadPLTSymbols(Elf* elf, Elf_Scn *pltSection, Elf_Scn *relPltSection, Elf_Scn *dynsymSection)
+{
+  GElf_Shdr header;
+
+  gelf_getshdr(pltSection, &header);
+  Address symStart = header.sh_addr;
+  Count symSize = header.sh_entsize;
+
+  gelf_getshdr(relPltSection, &header);
+  bool isRela = header.sh_type == SHT_RELA;
+  size_t relPltCount = header.sh_size / header.sh_entsize;
+
+  gelf_getshdr(dynsymSection, &header);
+  int strtabIdx = header.sh_link;
+
+  Elf_Data* relPltData = elf_getdata(relPltSection, 0);
+  Elf_Data* dynsymData = elf_getdata(dynsymSection, 0);
+
+  for (size_t relPltIdx = 0; relPltIdx < relPltCount; relPltIdx++)
+  {
+    size_t symIdx;
+    if (isRela)
+    {
+      GElf_Rela rela;
+      gelf_getrela(relPltData, relPltIdx, &rela);
+      symIdx = GELF_R_SYM(rela.r_info);
+    }
+    else
+    {
+      GElf_Rel rel;
+      gelf_getrel(relPltData, relPltIdx, &rel);
+      symIdx = GELF_R_SYM(rel.r_info);
+    }
+
+    GElf_Sym elfSymbol;
+    gelf_getsym(dynsymData, symIdx, &elfSymbol);
+
+
+    ARSymbolData& symbolData = symbols[Range(symStart, symStart + symSize)];
+    symbolData.name = elf_strptr(elf, strtabIdx, elfSymbol.st_name);
+    symbolData.misc = ARSymbolData::MiscPLT;
+
+    symStart += symSize;
+  }
+
+  pltEndAddress = symStart;
+}
+
 void AddressResolverPrivate::loadSymbolsFromSection(Elf* elf, Elf_Scn *section)
 {
-  symbols.clear();
+  symbols.erase(symbols.lower_bound(Range(pltEndAddress)), symbols.end());
 
   GElf_Shdr sectionHeader;
   gelf_getshdr(section, &sectionHeader);
@@ -356,7 +432,7 @@ void AddressResolverPrivate::loadSymbolsFromSection(Elf* elf, Elf_Scn *section)
     {
       const ARSymbolData& oldSymbolData = insResult.first->second;
       // Sized functions better that asm labels and higer binding is also better
-      if ((oldSymbolData.size == 0 && symbolData.size != 0) || (oldSymbolData.binding < symbolData.binding))
+      if ((oldSymbolData.size == 0 && symbolData.size != 0) || (oldSymbolData.misc < symbolData.misc))
       {
         symbols.erase(insResult.first);
         symbolData.name = elf_strptr(elf, sectionHeader.sh_link, elfSymbol.st_name);

NEWS

@@ -1,5 +1,7 @@
 perfgrind 0.3
-* Allow to set arbitrary frequency in pgcollect via -F argument
+
+* Allow to set arbitrary frequency in pgcollect via -F argument.
+* Handling of hits in PLT added.
 
 perfgrind 0.2
 

TODO

@@ -6,9 +6,6 @@ Short and incomplete TODO list:
 
 - use debug link section in ELF for finding separate debug info.
 
-- handle hits in PLT. At the moment they are usually reported as hits in
-  _init@object function.
-
 - detect correct call from addresses. Currently we put cumulative count to
   instruction next after call.