Add support for reading ARM ELF build attributes.

Build attribute sections can now be read if they exist via ELFObjectFile, and
the llvm-readobj tool has been extended with an option to dump this information
if requested. Regression tests are also included which exercise these features.

Also update the docs with a fixed ARM ABI link and a new link to the Addenda
which provides the build attributes specification.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181009 91177308-0d34-0410-b5e6-96231b3b80d8

docs/CompilerWriterInfo.rst

@@ -18,7 +18,9 @@ ARM
 
 * `ARM documentation <http://www.arm.com/documentation/>`_ (`Processor Cores <http://www.arm.com/documentation/ARMProcessor_Cores/>`_ Cores)
 
-* `ABI <http://www.arm.com/products/DevTools/ABI.html>`_
+* `ELF ABI <http://infocenter.arm.com/help/topic/com.arm.doc.ihi0044e/IHI0044E_aaelf.pdf>`_
+
+* `Addenda to the ARM ABI <http://infocenter.arm.com/help/topic/com.arm.doc.ihi0045d/IHI0045D_ABI_addenda.pdf>`_
 
 * `ARM C Language Extensions <http://infocenter.arm.com/help/topic/com.arm.doc.ihi0053a/IHI0053A_acle.pdf>`_
 

include/llvm/Object/ELF.h

@@ -19,11 +19,13 @@
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/ADT/Triple.h"
+#include "llvm/Object/ELF_ARM.h"
 #include "llvm/Object/ObjectFile.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/ELF.h"
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/LEB128.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
@@ -601,6 +603,7 @@ class ELFObjectFile : public ObjectFile {
   const Elf_Shdr *dot_gnu_version_sec;   // .gnu.version
   const Elf_Shdr *dot_gnu_version_r_sec; // .gnu.version_r
   const Elf_Shdr *dot_gnu_version_d_sec; // .gnu.version_d
+  const Elf_Shdr *dot_arm_attributes_sec; // .ARM.attributes
 
   // Pointer to SONAME entry in dynamic string table
   // This is set the first time getLoadName is called.
@@ -643,6 +646,11 @@ class ELFObjectFile : public ObjectFile {
   const Elf_Shdr *getRelSection(DataRefImpl Rel) const {
     return getSection(Rel.w.b);
   }
+  // Helper to read a single ARM attribute at the given pointer and return the
+  // read pointer moved forward to the next attribute location.
+  uintptr_t readARMSingleAttribute(uintptr_t ReadPtr,
+                                  ARMBuildAttrs::ARMGenericBuildAttrInfo &Attrs,
+                                  SmallVector<unsigned, 16> &TagSet) const;
 
 public:
   bool            isRelocationHasAddend(DataRefImpl Rel) const;
@@ -838,6 +846,18 @@ class ELFObjectFile : public ObjectFile {
     return v->getType() == getELFType(ELFT::TargetEndianness == support::little,
                                       ELFT::Is64Bits);
   }
+
+  /// \brief Read the ARM build attributes of this object file.
+  /// \param Attrs The attributes container to put the attribute values.
+  /// \param TagsSet A list of attribute tags that were read.
+  error_code readARMBuildAttributes(
+                                  ARMBuildAttrs::ARMGenericBuildAttrInfo &Attrs,
+                                  SmallVector<unsigned, 16> &TagsSet) const;
+
+  /// \brief Checks if an ARM build attributes section exists.
+  bool hasARMBuildAttributes() const {
+    return dot_arm_attributes_sec ? true : false;
+  }
 };
 
 // Iterate through the version definitions, and place each Elf_Verdef
@@ -2330,6 +2350,7 @@ ELFObjectFile<ELFT>::ELFObjectFile(MemoryBuffer *Object, error_code &ec)
   , dot_gnu_version_sec(0)
   , dot_gnu_version_r_sec(0)
   , dot_gnu_version_d_sec(0)
+  , dot_arm_attributes_sec(0)
   , dt_soname(0)
  {
 
@@ -2421,6 +2442,13 @@ ELFObjectFile<ELFT>::ELFObjectFile(MemoryBuffer *Object, error_code &ec)
       dot_gnu_version_r_sec = sh;
       break;
     }
+    case ELF::SHT_ARM_ATTRIBUTES: {
+      if (dot_arm_attributes_sec != NULL)
+        // FIXME: Proper error handling.
+        report_fatal_error("More than one .arm.attributes section!");
+      dot_arm_attributes_sec = sh;
+      break;
+    }
     }
     ++sh;
   }
@@ -2970,6 +2998,164 @@ static inline error_code GetELFSymbolVersion(const ObjectFile *Obj,
   llvm_unreachable("Object passed to GetELFSymbolVersion() is not ELF");
 }
 
+template<class ELFT>
+error_code ELFObjectFile<ELFT>::readARMBuildAttributes(
+                                  ARMBuildAttrs::ARMGenericBuildAttrInfo &Attrs,
+                                  SmallVector<unsigned, 16> &TagsSet) const {
+  if (getArch() != Triple::arm)
+    return object_error::invalid_file_type;
+  if (!dot_arm_attributes_sec)
+    return object_error::parse_failed;
+
+  const char *SecStart = (const char*)base() +
+                          dot_arm_attributes_sec->sh_offset;
+  const char *SecEnd = SecStart + dot_arm_attributes_sec->sh_size;
+  char format_version = *SecStart;
+  if (format_version != ARMBuildAttrs::Format_Version)
+    return object_error::parse_failed;
+
+  uintptr_t SSectionPtr = (uintptr_t)SecStart + 1;
+  uintptr_t ReadPtr = SSectionPtr;
+  // Begin reading section after format-version byte
+  while (ReadPtr < (uintptr_t)SecEnd) {
+    // Read a subsection, starting with: <section-length> "vendor-name"
+    // For now, we only care about the "aeabi" pseudo-vendor subsection.
+    uint32_t SSectionLen = *(Elf_Word*)ReadPtr;
+    ReadPtr += sizeof(uint32_t);
+    StringRef Vendor((char*)(ReadPtr));
+    ReadPtr += Vendor.size() + 1; // Vendor string + NUL byte
+
+    if (Vendor != "aeabi") {
+      SSectionPtr += SSectionLen;
+      ReadPtr = SSectionPtr;
+      continue; //skip to the next sub-section
+    }
+
+    bool FoundFileTag = false;
+    uintptr_t SSSectionPtr = ReadPtr;
+    uint32_t SSSectionLen = *(Elf_Word*)ReadPtr;
+    // Found aeabi subsection, now find the File scope tag.
+    while (ReadPtr < SSectionPtr + SSectionLen) {
+      unsigned n = 0;
+      uint64_t Tag = decodeULEB128((uint8_t*)ReadPtr, &n);
+      ReadPtr += n;
+      SSSectionLen = *(Elf_Word*)ReadPtr;
+      if (Tag == ARMBuildAttrs::File) {
+        FoundFileTag = true;
+        break;
+      }
+      // We only handle File scope attributes, skip ahead to the next
+      // sub-subsection.
+      SSSectionPtr += SSSectionLen;
+      ReadPtr = SSSectionPtr;
+    }
+
+    if (!FoundFileTag)
+      return object_error::parse_failed;
+
+    ReadPtr += sizeof(uint32_t);
+    while (ReadPtr < SSSectionPtr + SSSectionLen) {
+      // Read any number of attributes.
+      // Attributes are pairs of <uleb128, uleb128> or <uleb128, NTBS>.
+      ReadPtr = readARMSingleAttribute(ReadPtr, Attrs, TagsSet);
+    }
+    Attrs.setValid(true);
+  }
+  return object_error::success;
+}
+
+#define SWITCH_ARM_ATTR_READ_ULEB(X) case ARMBuildAttrs::X: \
+  UlebValue = decodeULEB128((uint8_t*)ReadPtr, &n); \
+  ReadPtr += n; \
+  Attrs.Tag_##X = UlebValue; \
+  TagsSet.push_back(tag); \
+  break;
+
+template<class ELFT>
+uintptr_t ELFObjectFile<ELFT>::readARMSingleAttribute(uintptr_t ReadPtr,
+                                 ARMBuildAttrs::ARMGenericBuildAttrInfo &Attrs,
+                                 SmallVector<unsigned, 16> &TagsSet) const {
+  // The ABI says that tags in the range 0-63 must be handled by tools.
+  unsigned n = 0;
+  uint64_t tagInt = decodeULEB128((uint8_t*)ReadPtr, &n);
+  ARMBuildAttrs::AttrType tag = (ARMBuildAttrs::AttrType)tagInt;
+  ReadPtr += n;
+  uint64_t UlebValue = 0;
+  StringRef StrValue;
+  switch (tag) {
+  case ARMBuildAttrs::CPU_arch: // uleb128
+    UlebValue = decodeULEB128((uint8_t*)ReadPtr, &n);
+    ReadPtr += n;
+    Attrs.Tag_CPU_arch = (ARMBuildAttrs::CPUArch)UlebValue;
+    TagsSet.push_back(tag);
+    break;
+  case ARMBuildAttrs::CPU_raw_name: // NTBS
+    StrValue = (char*)ReadPtr;
+    Attrs.Tag_CPU_raw_name = StrValue;
+    TagsSet.push_back(ARMBuildAttrs::CPU_raw_name);
+    ReadPtr += StrValue.size() + 1;
+    break;
+  case ARMBuildAttrs::CPU_name: //NTBS
+    StrValue = (char*)ReadPtr;
+    Attrs.Tag_CPU_name = StrValue;
+    TagsSet.push_back(ARMBuildAttrs::CPU_name);
+    ReadPtr += StrValue.size() + 1;
+    break;
+  case ARMBuildAttrs::CPU_arch_profile: // uleb128
+    UlebValue = decodeULEB128((uint8_t*)ReadPtr, &n);
+    ReadPtr += n;
+    Attrs.Tag_CPU_arch_profile =
+      (ARMBuildAttrs::CPUArchProfile)UlebValue;
+    TagsSet.push_back(tag);
+    break;
+  SWITCH_ARM_ATTR_READ_ULEB(ARM_ISA_use)
+  SWITCH_ARM_ATTR_READ_ULEB(THUMB_ISA_use)
+  SWITCH_ARM_ATTR_READ_ULEB(FP_arch)
+  SWITCH_ARM_ATTR_READ_ULEB(WMMX_arch)
+  SWITCH_ARM_ATTR_READ_ULEB(Advanced_SIMD_arch)
+  SWITCH_ARM_ATTR_READ_ULEB(FP_HP_extension)
+  SWITCH_ARM_ATTR_READ_ULEB(CPU_unaligned_access)
+  SWITCH_ARM_ATTR_READ_ULEB(MPextension_use)
+  SWITCH_ARM_ATTR_READ_ULEB(DIV_use)
+  SWITCH_ARM_ATTR_READ_ULEB(T2EE_use)
+  SWITCH_ARM_ATTR_READ_ULEB(Virtualization_use)
+  SWITCH_ARM_ATTR_READ_ULEB(ABI_optimization_goals)
+  SWITCH_ARM_ATTR_READ_ULEB(ABI_FP_optimization_goals)
+  SWITCH_ARM_ATTR_READ_ULEB(PCS_config)
+  SWITCH_ARM_ATTR_READ_ULEB(ABI_PCS_R9_use)
+  SWITCH_ARM_ATTR_READ_ULEB(ABI_PCS_RW_data)
+  SWITCH_ARM_ATTR_READ_ULEB(ABI_PCS_RO_data)
+  SWITCH_ARM_ATTR_READ_ULEB(ABI_PCS_GOT_use)
+  SWITCH_ARM_ATTR_READ_ULEB(ABI_PCS_wchar_t)
+  SWITCH_ARM_ATTR_READ_ULEB(ABI_enum_size)
+  SWITCH_ARM_ATTR_READ_ULEB(ABI_align8_needed)
+  SWITCH_ARM_ATTR_READ_ULEB(ABI_align8_preserved)
+  SWITCH_ARM_ATTR_READ_ULEB(ABI_FP_rounding)
+  SWITCH_ARM_ATTR_READ_ULEB(ABI_FP_denormal)
+  SWITCH_ARM_ATTR_READ_ULEB(ABI_FP_number_model)
+  SWITCH_ARM_ATTR_READ_ULEB(ABI_FP_exceptions)
+  SWITCH_ARM_ATTR_READ_ULEB(ABI_FP_user_exceptions)
+  SWITCH_ARM_ATTR_READ_ULEB(ABI_HardFP_use)
+  SWITCH_ARM_ATTR_READ_ULEB(ABI_VFP_args)
+  default:
+    // Unhandled build attribute tag, according to the spec we should be able
+    // to infer the type of the value from (tag % 2) and skip over it.
+    if (tag & 0x1) {
+      // Value should be a null terminated byte string
+      StrValue = (char*)ReadPtr;
+      ReadPtr += StrValue.size() + 1;
+    } else {
+      // Value should be a uleb128
+      UlebValue = decodeULEB128((uint8_t*)ReadPtr, &n);
+      ReadPtr += n;
+    }
+    break;
+  }
+  return ReadPtr;
+}
+#undef SWITCH_ARM_ATTR_READ_ULEB
+
+
 /// This function returns the hash value for a symbol in the .dynsym section
 /// Name of the API remains consistent as specified in the libelf
 /// REF : http://www.sco.com/developers/gabi/latest/ch5.dynamic.html#hash