LLVM: Add ELF Note section to NaCl object files identifying them as such to gold

This is needed to switch the native linker to one based on upstream binutils
2.23
R=mseaborn@chromium.org
BUG= https://code.google.com/p/nativeclient/issues/detail?id=2971
also related to bug https://code.google.com/p/nativeclient/issues/detail?id=3424

Review URL: https://codereview.chromium.org/15067009

14 files changed, 217 insertions, 35 deletions

diff --git a/include/llvm/MC/MCNaCl.h b/include/llvm/MC/MCNaCl.h
new file mode 100644
index 0000000000..cf9b23ec1c
--- /dev/null
+++ b/include/llvm/MC/MCNaCl.h
@@ -0,0 +1,18 @@
+//===- MCNaCl.h - NaCl-specific code for MC  --------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+namespace llvm {
+class MCContext;
+class MCStreamer;
+class Triple;
+/// Initialize target-specific bundle alignment and emit target-specific NaCl
+/// ELF note sections.
+void initializeNaClMCStreamer(MCStreamer &Streamer, MCContext &Ctx,
+                              const Triple &TheTriple);
+}
diff --git a/include/llvm/Support/ELF.h b/include/llvm/Support/ELF.h
index 5e70debea1..d665cbd18f 100644
--- a/include/llvm/Support/ELF.h
+++ b/include/llvm/Support/ELF.h
@@ -1324,6 +1324,13 @@ enum {
   PF_MASKPROC = 0xf0000000 // Bits for processor-specific semantics.
 };
 
+// @LOCALMOD-BEGIN
+// Note segment descriptor types (for object files).
+enum {
+  NT_VERSION  = 1          // Note contains a version string.
+};
+// @LOCALMOD-END
+
 // Dynamic table entry for ELF32.
 struct Elf32_Dyn
 {
diff --git a/lib/MC/CMakeLists.txt b/lib/MC/CMakeLists.txt
index db882c020b..f2f78333b7 100644
--- a/lib/MC/CMakeLists.txt
+++ b/lib/MC/CMakeLists.txt
@@ -23,6 +23,7 @@ add_llvm_library(LLVMMC
   MCMachOStreamer.cpp
   MCMachObjectTargetWriter.cpp
   MCModule.cpp
+  MCNaCl.cpp
   MCNullStreamer.cpp
   MCObjectFileInfo.cpp
   MCObjectStreamer.cpp
diff --git a/lib/MC/MCNaCl.cpp b/lib/MC/MCNaCl.cpp
new file mode 100644
index 0000000000..4a6363d6c0
--- /dev/null
+++ b/lib/MC/MCNaCl.cpp
@@ -0,0 +1,74 @@
+//===- lib/MC/MCNaCl.cpp - NaCl-specific MC implementation ----------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/MC/MCNaCl.h"
+#include "llvm/ADT/Triple.h"
+#include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCSectionELF.h"
+#include "llvm/MC/MCStreamer.h"
+#include "llvm/Support/ELF.h"
+
+static const char NoteNamespace[] = "NaCl";
+
+namespace llvm {
+void initializeNaClMCStreamer(MCStreamer &Streamer, MCContext &Ctx,
+                              const Triple &TheTriple) {
+  assert(TheTriple.isOSNaCl());
+  const char *NoteName;
+  const char *NoteArch;
+  unsigned BundleAlign;
+  switch (TheTriple.getArch()) {
+    case Triple::arm:
+      NoteName = ".note.NaCl.ABI.arm";
+      NoteArch = "arm";
+      BundleAlign = 4;
+      break;
+    case Triple::mipsel:
+      NoteName = ".note.NaCl.ABI.mipsel";
+      NoteArch = "mipsel";
+      BundleAlign = 4;
+      break;
+    case Triple::x86:
+      NoteName = ".note.NaCl.ABI.x86-32";
+      NoteArch = "x86-32";
+      BundleAlign = 5;
+      break;
+    case Triple::x86_64:
+      NoteName = ".note.NaCl.ABI.x86-64";
+      NoteArch = "x86-64";
+      BundleAlign = 5;
+      break;
+    default:
+      report_fatal_error("Unsupported architecture for NaCl");
+  }
+
+  // Set bundle-alignment as required by the NaCl ABI for the target.
+  Streamer.EmitBundleAlignMode(BundleAlign);
+
+  // Emit an ELF Note section in its own COMDAT group which identifies NaCl
+  // object files to the gold linker, so it can use the NaCl layout.
+  const MCSection *Note = Ctx.getELFSection(
+      NoteName, ELF::SHT_NOTE, ELF::SHF_ALLOC | ELF::SHF_GROUP,
+      SectionKind::getReadOnly(), 0, NoteName);
+
+  // TODO(dschuff) This should probably use PushSection and PopSection, but
+  // PopSection will assert if there haven't been any other sections switched to
+  // yet.
+  Streamer.SwitchSection(Note);
+  Streamer.EmitIntValue(strlen(NoteNamespace) + 1, 4);
+  Streamer.EmitIntValue(strlen(NoteArch) + 1, 4);
+  Streamer.EmitIntValue(ELF::NT_VERSION, 4);
+  Streamer.EmitBytes(NoteNamespace);
+  Streamer.EmitIntValue(0, 1); // NUL terminator
+  Streamer.EmitValueToAlignment(4);
+  Streamer.EmitBytes(NoteArch);
+  Streamer.EmitIntValue(0, 1); // NUL terminator
+  Streamer.EmitValueToAlignment(4);
+}
+} // namespace llvm
diff --git a/lib/Target/ARM/ARMAsmPrinter.cpp b/lib/Target/ARM/ARMAsmPrinter.cpp
index c48df8a96f..0143d95c19 100644
--- a/lib/Target/ARM/ARMAsmPrinter.cpp
+++ b/lib/Target/ARM/ARMAsmPrinter.cpp
@@ -40,6 +40,7 @@
 #include "llvm/MC/MCELFStreamer.h"
 #include "llvm/MC/MCInst.h"
 #include "llvm/MC/MCInstBuilder.h"
+#include "llvm/MC/MCNaCl.h"
 #include "llvm/MC/MCObjectStreamer.h"
 #include "llvm/MC/MCSectionMachO.h"
 #include "llvm/MC/MCStreamer.h"
@@ -733,11 +734,15 @@ void ARMAsmPrinter::EmitStartOfAsmFile(Module &M) {
     emitAttributes();
 
   // @LOCALMOD-BEGIN
-  if (Subtarget->isTargetNaCl() && OutStreamer.hasRawTextSupport()) {
-    std::string str;
-    raw_string_ostream OS(str);
-    EmitSFIHeaders(OS);
-    OutStreamer.EmitRawText(StringRef(OS.str()));
+  if (Subtarget->isTargetNaCl()) {
+    if (OutStreamer.hasRawTextSupport()) {
+      std::string str;
+      raw_string_ostream OS(str);
+      EmitSFIHeaders(OS);
+      OutStreamer.EmitRawText(StringRef(OS.str()));
+    }
+    initializeNaClMCStreamer(OutStreamer, OutContext,
+                             Subtarget->getTargetTriple());
   }
   // @LOCALMOD-END
 }
diff --git a/lib/Target/ARM/MCTargetDesc/ARMMCTargetDesc.cpp b/lib/Target/ARM/MCTargetDesc/ARMMCTargetDesc.cpp
index 2c155aaf40..3d6e99f664 100644
--- a/lib/Target/ARM/MCTargetDesc/ARMMCTargetDesc.cpp
+++ b/lib/Target/ARM/MCTargetDesc/ARMMCTargetDesc.cpp
@@ -208,13 +208,9 @@ static MCStreamer *createMCStreamer(const Target &T, StringRef TT,
   if (TheTriple.isOSWindows()) {
     llvm_unreachable("ARM does not support Windows COFF format");
   }
-  // @LOCALMOD-BEGIN
-  MCStreamer *Streamer = createARMELFStreamer(Ctx, MAB, OS, Emitter, false,
-                           NoExecStack, TheTriple.getArch() == Triple::thumb);
-  if (TheTriple.isOSNaCl())
-    Streamer->EmitBundleAlignMode(4);
-  return Streamer;
-  // @LOCALMOD-END
+
+  return createARMELFStreamer(Ctx, MAB, OS, Emitter, false, NoExecStack,
+                              TheTriple.getArch() == Triple::thumb);
 }
 
 static MCInstPrinter *createARMMCInstPrinter(const Target &T,
diff --git a/lib/Target/Mips/MCTargetDesc/MipsMCTargetDesc.cpp b/lib/Target/Mips/MCTargetDesc/MipsMCTargetDesc.cpp
index 2e2f4b9612..be83b54b61 100644
--- a/lib/Target/Mips/MCTargetDesc/MipsMCTargetDesc.cpp
+++ b/lib/Target/Mips/MCTargetDesc/MipsMCTargetDesc.cpp
@@ -132,16 +132,7 @@ static MCStreamer *createMCStreamer(const Target &T, StringRef TT,
                                     bool NoExecStack) {
   Triple TheTriple(TT);
 
-  // @LOCALMOD-BEGIN
-  if (TheTriple.isOSNaCl()) {
-    MCStreamer *Streamer = createMipsELFStreamer(Ctx, MAB, _OS, _Emitter,
-                                                 RelaxAll, NoExecStack);
-    Streamer->EmitBundleAlignMode(4);
-    return Streamer;
-  } else {
-    return createMipsELFStreamer(Ctx, MAB, _OS, _Emitter, RelaxAll, NoExecStack);
-  }
-  // @LOCALMOD-END
+  return createMipsELFStreamer(Ctx, MAB, _OS, _Emitter, RelaxAll, NoExecStack);
 }
 
 extern "C" void LLVMInitializeMipsTargetMC() {
diff --git a/lib/Target/Mips/MipsAsmPrinter.cpp b/lib/Target/Mips/MipsAsmPrinter.cpp
index 61fb94d531..fc45fd273f 100644
--- a/lib/Target/Mips/MipsAsmPrinter.cpp
+++ b/lib/Target/Mips/MipsAsmPrinter.cpp
@@ -34,6 +34,7 @@
 #include "llvm/IR/Instructions.h"
 #include "llvm/MC/MCAsmInfo.h"
 #include "llvm/MC/MCInst.h"
+#include "llvm/MC/MCNaCl.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSymbol.h"
 #include "llvm/Support/ELF.h"
@@ -568,11 +569,15 @@ void MipsAsmPrinter::EmitStartOfAsmFile(Module &M) {
     OutStreamer.EmitRawText(StringRef("\t.previous"));
 
   // @LOCALMOD-START
-  if (Subtarget->isTargetNaCl() && OutStreamer.hasRawTextSupport()) {
-    std::string str;
-    raw_string_ostream OS(str);
-    EmitMipsSFIHeaders(OS);
-    OutStreamer.EmitRawText(StringRef(OS.str()));
+  if (Subtarget->isTargetNaCl()) {
+    if (OutStreamer.hasRawTextSupport()) {
+      std::string str;
+      raw_string_ostream OS(str);
+      EmitMipsSFIHeaders(OS);
+      OutStreamer.EmitRawText(StringRef(OS.str()));
+    }
+    initializeNaClMCStreamer(OutStreamer, OutContext,
+                             Triple(Subtarget->getTargetTriple()));
   }
   // @LOCALMOD-END
 }
diff --git a/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.cpp b/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.cpp
index c67bb944b6..5e84530cd7 100644
--- a/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.cpp
+++ b/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.cpp
@@ -366,14 +366,7 @@ static MCStreamer *createMCStreamer(const Target &T, StringRef TT,
   if (TheTriple.isOSWindows() && TheTriple.getEnvironment() != Triple::ELF)
     return createWinCOFFStreamer(Ctx, MAB, *_Emitter, _OS, RelaxAll);
 
-  // @LOCALMOD-BEGIN
-  MCStreamer *Streamer = createELFStreamer(Ctx, MAB, _OS, _Emitter,
-                                           RelaxAll, NoExecStack);
-  if (TheTriple.isOSNaCl())
-    Streamer->EmitBundleAlignMode(5);
-
-  return Streamer;
-  // @LOCALMOD-END
+  return createELFStreamer(Ctx, MAB, _OS, _Emitter, RelaxAll, NoExecStack);
 }
 
 static MCInstPrinter *createX86MCInstPrinter(const Target &T,
diff --git a/lib/Target/X86/X86AsmPrinter.cpp b/lib/Target/X86/X86AsmPrinter.cpp
index 2eb75b558b..032d83aac0 100644
--- a/lib/Target/X86/X86AsmPrinter.cpp
+++ b/lib/Target/X86/X86AsmPrinter.cpp
@@ -31,6 +31,7 @@
 #include "llvm/MC/MCAsmInfo.h"
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCExpr.h"
+#include "llvm/MC/MCNaCl.h"
 #include "llvm/MC/MCSectionMachO.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSymbol.h"
@@ -547,6 +548,11 @@ bool X86AsmPrinter::PrintAsmMemoryOperand(const MachineInstr *MI,
 void X86AsmPrinter::EmitStartOfAsmFile(Module &M) {
   if (Subtarget->isTargetEnvMacho())
     OutStreamer.SwitchSection(getObjFileLowering().getTextSection());
+  // @LOCALMOD-BEGIN
+  if (Subtarget->isTargetNaCl())
+    initializeNaClMCStreamer(OutStreamer, OutContext,
+                             Subtarget->getTargetTriple());
+  // @LOCALMOD-END
 }
 
 
diff --git a/test/MC/ARM/elf-note-nacl.ll b/test/MC/ARM/elf-note-nacl.ll
new file mode 100644
index 0000000000..8551cf52b4
--- /dev/null
+++ b/test/MC/ARM/elf-note-nacl.ll
@@ -0,0 +1,22 @@
+; RUN: llc -filetype=obj -mtriple armv7-none-nacl-gnueabi %s -o - \
+; RUN:   | llvm-objdump -triple armv7 -s - | FileCheck %s
+
+; Tests that NaCl object files contain an ELF note section that identifies them
+; to the binutils gold linker
+
+define void @main() {
+  ret void
+}
+
+; There appears to be no way for llvm-objdump to show flags for sections, or
+; to dump groups like readelf.
+; CHECK: .group
+; CHECK: .note.NaCl.ABI.arm
+; The contents of the words in the note section should be:
+;   sizeof "NaCl"
+;   sizeof "arm"
+;   1 (NT_VERSION)
+;   "NaCl" with nul termination and padding to align 4
+;   "arm" with nul termination and padding to align 4
+; CHECK-NEXT: 0000 05000000 04000000 01000000 4e61436c
+; CHECK-NEXT: 0010 00000000 61726d00
diff --git a/test/MC/Mips/elf-note-nacl.ll b/test/MC/Mips/elf-note-nacl.ll
new file mode 100644
index 0000000000..0361eff25e
--- /dev/null
+++ b/test/MC/Mips/elf-note-nacl.ll
@@ -0,0 +1,22 @@
+; RUN: llc -filetype=obj -mtriple mipsel-none-nacl %s -o - \
+; RUN:   | llvm-objdump -triple mipsel -s - | FileCheck %s
+
+; Tests that NaCl object files contain an ELF note section that identifies them
+; to the binutils gold linker
+
+define void @main() {
+  ret void
+}
+
+; There appears to be no way for llvm-objdump to show flags for sections, or
+; to dump groups like readelf.
+; CHECK: .group
+; CHECK: .note.NaCl.ABI.mipsel
+; The contents of the words in the note section should be:
+;   sizeof "NaCl"
+;   sizeof "mipsel"
+;   1 (NT_VERSION)
+;   "NaCl" with nul termination and padding to align 4
+;   "mipsel" with nul termination and padding to align 4
+; CHECK-NEXT: 0000 05000000 07000000 01000000 4e61436c
+; CHECK-NEXT: 0010 00000000 6d697073 656c0000
diff --git a/test/MC/X86/elf-note-nacl.ll b/test/MC/X86/elf-note-nacl.ll
new file mode 100644
index 0000000000..ce15455c84
--- /dev/null
+++ b/test/MC/X86/elf-note-nacl.ll
@@ -0,0 +1,36 @@
+; RUN: llc -filetype=obj -mtriple i686-none-nacl %s -o - \
+; RUN:   | llvm-objdump -triple i686 -s - | FileCheck --check-prefix=I386 %s
+
+; RUN: llc -filetype=obj -mtriple x86_64-none-nacl %s -o - \
+; RUN:   | llvm-objdump -triple x86_64 -s - | FileCheck --check-prefix=X8664 %s
+
+; Tests that NaCl object files contain an ELF note section that identifies them
+; to the binutils gold linker
+
+define void @main() {
+  ret void
+}
+
+; There appears to be no way for llvm-objdump to show flags for sections, or
+; to dump groups like readelf.
+; I386: .group
+; I386: .note.NaCl.ABI.x86-32
+; The contents of the words in the note section should be:
+;   sizeof "NaCl"
+;   sizeof "x86-32"
+;   1 (NT_VERSION)
+;   "NaCl" with nul termination and padding to align 4
+;   "x86-32" with nul termination and padding to align 4
+; I386-NEXT: 0000 05000000 07000000 01000000 4e61436c
+; I386-NEXT: 0010 00000000 7838362d 33320000
+
+; X8664: .group
+; X8664: .note.NaCl.ABI.x86-64
+; The contents of the words in the note section should be:
+;   sizeof "NaCl"
+;   sizeof "x86-64"
+;   1 (NT_VERSION)
+;   "NaCl" with nul termination and padding to align 4
+;   q"x86-64" with nul termination and padding to align 4
+; X8664-NEXT: 0000 05000000 07000000 01000000 4e61436c
+; X8664-NEXT: 0010 00000000 7838362d 36340000
diff --git a/tools/llvm-mc/llvm-mc.cpp b/tools/llvm-mc/llvm-mc.cpp
index 243899bb88..11304454f0 100644
--- a/tools/llvm-mc/llvm-mc.cpp
+++ b/tools/llvm-mc/llvm-mc.cpp
@@ -20,6 +20,7 @@
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCInstPrinter.h"
 #include "llvm/MC/MCInstrInfo.h"
+#include "llvm/MC/MCNaCl.h"
 #include "llvm/MC/MCObjectFileInfo.h"
 #include "llvm/MC/MCParser/AsmLexer.h"
 #include "llvm/MC/MCRegisterInfo.h"
@@ -453,6 +454,11 @@ int main(int argc, char **argv) {
     Str.reset(TheTarget->createMCObjectStreamer(TripleName, Ctx, *MAB,
                                                 FOS, CE, RelaxAll,
                                                 NoExecStack));
+    // @LOCALMOD-BEGIN
+    Triple T(TripleName);
+    if (T.isOSNaCl())
+      initializeNaClMCStreamer(*Str.get(), Ctx, T);
+    // @LOCALMOD-END
   }
 
   int Res = 1;