[ELF] - Implemented basic location counter support.

This patch implements location counter support. It also separates assign addresses for sections to assignAddressesScript() if it scipt exists. Main testcase is test/ELF/linkerscript-locationcounter.s, It contains some work with location counter. It is basic now. Implemented location counter assignment and '+' operations. Patch by myself with LOTS of comments and design suggestions from Rui Ueyama. Differential revision: http://reviews.llvm.org/D18499 llvm-svn: 266457
llvm · Apr 15, 2016 · ea25877 · ea25877
1 parent 7950b12
commit ea25877
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Showing 8 changed files with 280 additions and 28 deletions.
diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
@@ -17,20 +17,55 @@
 #include "Config.h"
 #include "Driver.h"
 #include "InputSection.h"
+#include "OutputSections.h"
 #include "ScriptParser.h"
 #include "SymbolTable.h"
+#include "llvm/Support/ELF.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/StringSaver.h"
 
 using namespace llvm;
+using namespace llvm::ELF;
 using namespace llvm::object;
 using namespace lld;
 using namespace lld::elf;
 
 LinkerScript *elf::Script;
 
+static uint64_t getInteger(StringRef S) {
+  uint64_t V;
+  if (S.getAsInteger(0, V)) {
+    error("malformed number: " + S);
+    return 0;
+  }
+  return V;
+}
+
+// Evaluates the expression given by list of tokens.
+uint64_t LinkerScript::evaluate(std::vector<StringRef> &Tokens,
+                                uint64_t LocCounter) {
+  uint64_t Result = 0;
+  for (size_t I = 0, E = Tokens.size(); I < E; ++I) {
+    // Each second token should be '+' as this is the
+    // only operator we support now.
+    if (I % 2 == 1) {
+      if (Tokens[I] == "+")
+        continue;
+      error("error in location counter expression");
+      return 0;
+    }
+
+    StringRef Tok = Tokens[I];
+    if (Tok == ".")
+      Result += LocCounter;
+    else
+      Result += getInteger(Tok);
+  }
+  return Result;
+}
+
 template <class ELFT>
 SectionRule *LinkerScript::find(InputSectionBase<ELFT> *S) {
   for (SectionRule &R : Sections)
@@ -55,6 +90,66 @@ template <class ELFT> bool LinkerScript::shouldKeep(InputSectionBase<ELFT> *S) {
   return R && R->Keep;
 }
 
+// This method finalizes the Locations list. Adds neccesary locations for
+// orphan sections, what prepares it for futher use without
+// changes in LinkerScript::assignAddresses().
+template <class ELFT>
+void LinkerScript::fixupLocations(std::vector<OutputSectionBase<ELFT> *> &S) {
+  // Orphan sections are sections present in the input files which
+  // are not explicitly placed into the output file by the linker
+  // script. We place orphan sections at end of file. Other linkers places
+  // them using some heuristics as described in
+  // https://sourceware.org/binutils/docs/ld/Orphan-Sections.html#Orphan-Sections.
+  for (OutputSectionBase<ELFT> *Sec : S) {
+    StringRef Name = Sec->getName();
+    auto I = std::find(SectionOrder.begin(), SectionOrder.end(), Name);
+    if (I == SectionOrder.end())
+      Locations.push_back({Command::Section, {}, {Name}});
+  }
+}
+
+template <class ELFT>
+void LinkerScript::assignAddresses(std::vector<OutputSectionBase<ELFT> *> &S) {
+  typedef typename ELFT::uint uintX_t;
+
+  Script->fixupLocations(S);
+
+  uintX_t ThreadBssOffset = 0;
+  uintX_t VA =
+      Out<ELFT>::ElfHeader->getSize() + Out<ELFT>::ProgramHeaders->getSize();
+
+  for (LocationNode &Node : Locations) {
+    if (Node.Type == Command::Expr) {
+      VA = evaluate(Node.Expr, VA);
+      continue;
+    }
+
+    auto I =
+        std::find_if(S.begin(), S.end(), [&](OutputSectionBase<ELFT> *Sec) {
+          return Sec->getName() == Node.SectionName;
+        });
+    if (I == S.end())
+      continue;
+
+    OutputSectionBase<ELFT> *Sec = *I;
+    uintX_t Align = Sec->getAlign();
+    if ((Sec->getFlags() & SHF_TLS) && Sec->getType() == SHT_NOBITS) {
+      uintX_t TVA = VA + ThreadBssOffset;
+      TVA = alignTo(TVA, Align);
+      Sec->setVA(TVA);
+      ThreadBssOffset = TVA - VA + Sec->getSize();
+      continue;
+    }
+
+    if (Sec->getFlags() & SHF_ALLOC) {
+      VA = alignTo(VA, Align);
+      Sec->setVA(VA);
+      VA += Sec->getSize();
+      continue;
+    }
+  }
+}
+
 ArrayRef<uint8_t> LinkerScript::getFiller(StringRef Name) {
   auto I = Filler.find(Name);
   if (I == Filler.end())
@@ -126,6 +221,7 @@ class elf::ScriptParser final : public elf::ScriptParserBase {
   void readSearchDir();
   void readSections();
 
+  void readLocationCounterValue();
   void readOutputSectionDescription();
   void readSectionPatterns(StringRef OutSec, bool Keep);
 
@@ -287,8 +383,13 @@ void ScriptParser::readSearchDir() {
 
 void ScriptParser::readSections() {
   expect("{");
-  while (!Error && !skip("}"))
-    readOutputSectionDescription();
+  while (!Error && !skip("}")) {
+    StringRef Tok = peek();
+    if (Tok == ".")
+      readLocationCounterValue();
+    else
+      readOutputSectionDescription();
+  }
 }
 
 void ScriptParser::readSectionPatterns(StringRef OutSec, bool Keep) {
@@ -297,9 +398,25 @@ void ScriptParser::readSectionPatterns(StringRef OutSec, bool Keep) {
     Script->Sections.emplace_back(OutSec, next(), Keep);
 }
 
+void ScriptParser::readLocationCounterValue() {
+  expect(".");
+  expect("=");
+  Script->Locations.push_back({Command::Expr, {}, {}});
+  LocationNode &Node = Script->Locations.back();
+  while (!Error) {
+    StringRef Tok = next();
+    if (Tok == ";")
+      break;
+    Node.Expr.push_back(Tok);
+  }
+  if (Node.Expr.empty())
+    error("error in location counter expression");
+}
+
 void ScriptParser::readOutputSectionDescription() {
   StringRef OutSec = next();
   Script->SectionOrder.push_back(OutSec);
+  Script->Locations.push_back({Command::Section, {}, {OutSec}});
   expect(":");
   expect("{");
   while (!Error && !skip("}")) {
@@ -340,6 +457,7 @@ static bool isUnderSysroot(StringRef Path) {
 void LinkerScript::read(MemoryBufferRef MB) {
   StringRef Path = MB.getBufferIdentifier();
   ScriptParser(&Alloc, MB.getBuffer(), isUnderSysroot(Path)).run();
+  Exists = true;
 }
 
 template StringRef LinkerScript::getOutputSection(InputSectionBase<ELF32LE> *);
@@ -356,3 +474,12 @@ template bool LinkerScript::shouldKeep(InputSectionBase<ELF32LE> *);
 template bool LinkerScript::shouldKeep(InputSectionBase<ELF32BE> *);
 template bool LinkerScript::shouldKeep(InputSectionBase<ELF64LE> *);
 template bool LinkerScript::shouldKeep(InputSectionBase<ELF64BE> *);
+
+template void
+LinkerScript::assignAddresses(std::vector<OutputSectionBase<ELF32LE> *> &);
+template void
+LinkerScript::assignAddresses(std::vector<OutputSectionBase<ELF32BE> *> &);
+template void
+LinkerScript::assignAddresses(std::vector<OutputSectionBase<ELF64LE> *> &);
+template void
+LinkerScript::assignAddresses(std::vector<OutputSectionBase<ELF64BE> *> &);
diff --git a/lld/ELF/LinkerScript.h b/lld/ELF/LinkerScript.h
@@ -21,6 +21,7 @@ namespace elf {
 
 class ScriptParser;
 template <class ELFT> class InputSectionBase;
+template <class ELFT> class OutputSectionBase;
 
 // This class represents each rule in SECTIONS command.
 class SectionRule {
@@ -40,6 +41,17 @@ class SectionRule {
   StringRef SectionPattern;
 };
 
+// This enum represents what we can observe in SECTIONS tag of script:
+// Expr is a location counter change, like ". = . + 0x1000"
+// Section is a description of output section, like ".data :..."
+enum class Command { Expr, Section };
+
+struct LocationNode {
+  Command Type;
+  std::vector<StringRef> Expr;
+  StringRef SectionName;
+};
+
 // This is a runner of the linker script.
 class LinkerScript {
   friend class ScriptParser;
@@ -53,9 +65,16 @@ class LinkerScript {
   ArrayRef<uint8_t> getFiller(StringRef Name);
   template <class ELFT> bool isDiscarded(InputSectionBase<ELFT> *S);
   template <class ELFT> bool shouldKeep(InputSectionBase<ELFT> *S);
+  template <class ELFT>
+  void assignAddresses(std::vector<OutputSectionBase<ELFT> *> &S);
   int compareSections(StringRef A, StringRef B);
 
+  bool Exists = false;
+
 private:
+  template <class ELFT>
+  void fixupLocations(std::vector<OutputSectionBase<ELFT> *> &);
+  uint64_t evaluate(std::vector<StringRef> &Tokens, uint64_t LocCounter);
   template <class ELFT> SectionRule *find(InputSectionBase<ELFT> *S);
 
   // SECTIONS commands.
@@ -67,6 +86,9 @@ class LinkerScript {
   // Section fill attribute for each section.
   llvm::StringMap<std::vector<uint8_t>> Filler;
 
+  // Used to assign addresses to sections.
+  std::vector<LocationNode> Locations;
+
   llvm::BumpPtrAllocator Alloc;
 };
 

diff --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp
@@ -220,8 +220,12 @@ template <class ELFT> void Writer<ELFT>::run() {
   } else {
     createPhdrs();
     fixHeaders();
-    fixSectionAlignments();
-    assignAddresses();
+    if (Script->Exists) {
+      Script->assignAddresses(OutputSections);
+    } else {
+      fixSectionAlignments();
+      assignAddresses();
+    }
     assignFileOffsets();
     setPhdrs();
     fixAbsoluteSymbols();
@@ -1541,10 +1545,11 @@ template <class ELFT> void Writer<ELFT>::fixSectionAlignments() {
 // sections. These are special, we do not include them into output sections
 // list, but have them to simplify the code.
 template <class ELFT> void Writer<ELFT>::fixHeaders() {
-  Out<ELFT>::ElfHeader->setVA(Target->getVAStart());
+  uintX_t BaseVA = Script->Exists ? 0 : Target->getVAStart();
+  Out<ELFT>::ElfHeader->setVA(BaseVA);
   Out<ELFT>::ElfHeader->setFileOffset(0);
   uintX_t Off = Out<ELFT>::ElfHeader->getSize();
-  Out<ELFT>::ProgramHeaders->setVA(Off + Target->getVAStart());
+  Out<ELFT>::ProgramHeaders->setVA(Off + BaseVA);
   Out<ELFT>::ProgramHeaders->setFileOffset(Off);
 }
 

diff --git a/lld/test/ELF/end.s b/lld/test/ELF/end.s
@@ -36,13 +36,13 @@
 // NOBSS-NEXT:       SHF_ALLOC
 // NOBSS-NEXT:       SHF_WRITE
 // NOBSS-NEXT:     ]
-// NOBSS-NEXT:     Address: 0x12000
+// NOBSS-NEXT:     Address: 0x159
 // NOBSS-NEXT:     Offset:
 // NOBSS-NEXT:     Size: 2
 // NOBSS: ]
 // NOBSS: Symbols [
 // NOBSS:     Name: _end
-// NOBSS-NEXT:     Value: 0x12002
+// NOBSS-NEXT:     Value: 0x15B
 // NOBSS: ]
 
 // If the layout of the sections is changed, "_end" should point to the end of allocated address space.
@@ -60,13 +60,13 @@
 // TEXTATEND-NEXT:       SHF_ALLOC
 // TEXTATEND-NEXT:       SHF_EXECINSTR
 // TEXTATEND-NEXT:     ]
-// TEXTATEND-NEXT:     Address: 0x12000
+// TEXTATEND-NEXT:     Address: 0x160
 // TEXTATEND-NEXT:     Offset:
 // TEXTATEND-NEXT:     Size: 1
 // TEXTATEND: ]
 // TEXTATEND: Symbols [
 // TEXTATEND:     Name: _end
-// TEXTATEND-NEXT:     Value: 0x12001
+// TEXTATEND-NEXT:     Value: 0x161
 // TEXTATEND: ]
 
 .global _start,_end

diff --git a/lld/test/ELF/linkerscript-locationcounter.s b/lld/test/ELF/linkerscript-locationcounter.s
@@ -0,0 +1,74 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+# RUN: echo "SECTIONS { \
+# RUN:  . = 0x12341; \
+# RUN:  .data : { *(.data) } \
+# RUN:  . = . + 0x10000; \
+# RUN:  .text : { *(.text) } \
+# RUN: }" > %t.script
+
+# RUN: ld.lld %t --script %t.script -o %t2
+# RUN: llvm-readobj -s %t2 | FileCheck %s
+
+# CHECK:      Sections [
+# CHECK-NEXT:   Section {
+# CHECK-NEXT:     Index: 0
+# CHECK-NEXT:     Name:  (0)
+# CHECK-NEXT:     Type: SHT_NULL
+# CHECK-NEXT:     Flags [
+# CHECK-NEXT:     ]
+# CHECK-NEXT:     Address: 0x0
+# CHECK-NEXT:     Offset: 0x0
+# CHECK-NEXT:     Size: 0
+# CHECK-NEXT:     Link: 0
+# CHECK-NEXT:     Info: 0
+# CHECK-NEXT:     AddressAlignment: 0
+# CHECK-NEXT:     EntrySize: 0
+# CHECK-NEXT:   }
+# CHECK-NEXT:   Section {
+# CHECK-NEXT:     Index: 1
+# CHECK-NEXT:     Name: .data
+# CHECK-NEXT:     Type: SHT_PROGBITS
+# CHECK-NEXT:     Flags [
+# CHECK-NEXT:       SHF_ALLOC
+# CHECK-NEXT:       SHF_WRITE
+# CHECK-NEXT:     ]
+# CHECK-NEXT:     Address: 0x12341
+# CHECK-NEXT:     Offset: 0x158
+# CHECK-NEXT:     Size: 8
+# CHECK-NEXT:     Link: 0
+# CHECK-NEXT:     Info: 0
+# CHECK-NEXT:     AddressAlignment: 1
+# CHECK-NEXT:     EntrySize: 0
+# CHECK-NEXT:   }
+# CHECK-NEXT:   Section {
+# CHECK-NEXT:     Index: 2
+# CHECK-NEXT:     Name: .text
+# CHECK-NEXT:     Type: SHT_PROGBITS
+# CHECK-NEXT:     Flags [
+# CHECK-NEXT:       SHF_ALLOC
+# CHECK-NEXT:       SHF_EXECINSTR
+# CHECK-NEXT:     ]
+# CHECK-NEXT:     Address: 0x2234C
+# CHECK-NEXT:     Offset: 0x160
+# CHECK-NEXT:     Size: 1
+# CHECK-NEXT:     Link: 0
+# CHECK-NEXT:     Info: 0
+# CHECK-NEXT:     AddressAlignment: 4
+# CHECK-NEXT:     EntrySize: 0
+# CHECK-NEXT:   }
+
+# RUN: echo "SECTIONS { \
+# RUN:  . = 0x12Q41; \
+# RUN: }" > %t.script
+# RUN: not ld.lld %t --script %t.script -o %t2 2>&1 | \
+# RUN:  FileCheck --check-prefix=NUMERR %s
+# NUMERR: malformed number: 0x12Q41
+
+.globl _start;
+_start:
+nop
+
+.section .data
+.quad 0
+