Copy LLVM bitcode reader to generate a PNaCl wire format reader.

include/llvm/Bitcode/NaCl/NaClReaderWriter.h

 //===-- llvm/Bitcode/NaCl/NaClReaderWriter.h - ------------------*- C++ -*-===//
 //      NaCl Bitcode reader/writer.
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
-// This header defines interfaces to read and write LLVM bitcode files/streams.
+// This header defines interfaces to read and write NaCl bitcode wire format
+// files.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_BITCODE_NACL_NACLREADERWRITER_H
 #define LLVM_BITCODE_NACL_NACLREADERWRITER_H
 
+#include <string>
+
 namespace llvm {
+  class MemoryBuffer;
+  class DataStreamer;
+  class LLVMContext;
   class Module;
   class raw_ostream;
 
+  /// getNaClLazyBitcodeModule - Read the header of the specified bitcode buffer
+  /// and prepare for lazy deserialization of function bodies.  If successful,
+  /// this takes ownership of 'buffer' and returns a non-null pointer.  On
+  /// error, this returns null, *does not* take ownership of Buffer, and fills
+  /// in *ErrMsg with an error description if ErrMsg is non-null.
+  Module *getNaClLazyBitcodeModule(MemoryBuffer *Buffer,
+                                   LLVMContext &Context,
+                                   std::string *ErrMsg = 0);
+
+  /// getNaClStreamedBitcodeModule - Read the header of the specified stream
+  /// and prepare for lazy deserialization and streaming of function bodies.
+  /// On error, this returns null, and fills in *ErrMsg with an error
+  /// description if ErrMsg is non-null.
+  Module *getNaClStreamedBitcodeModule(const std::string &name,
+                                       DataStreamer *streamer,
+                                       LLVMContext &Context,
+                                       std::string *ErrMsg = 0);
+
+  /// NaClParseBitcodeFile - Read the specified bitcode file,
+  /// returning the module.  If an error occurs, this returns null and
+  /// fills in *ErrMsg if it is non-null.  This method *never* takes
+  /// ownership of Buffer.
+  Module *NaClParseBitcodeFile(MemoryBuffer *Buffer, LLVMContext &Context,
+                               std::string *ErrMsg = 0);
+
   /// NaClWriteBitcodeToFile - Write the specified module to the
   /// specified raw output stream, using PNaCl wire format.  For
   /// streams where it matters, the given stream should be in "binary"
   /// mode.
   void NaClWriteBitcodeToFile(const Module *M, raw_ostream &Out);
 
+  /// isNaClBitcodeWrapper - Return true if the given bytes are the
+  /// magic bytes for an LLVM IR bitcode wrapper.
+  ///
+  inline bool isNaClBitcodeWrapper(const unsigned char *BufPtr,
+                                   const unsigned char *BufEnd) {
+    // See if you can find the hidden message in the magic bytes :-).
+    // (Hint: it's a little-endian encoding.)
+    return BufPtr != BufEnd &&
+           BufPtr[0] == 0xDE &&
+           BufPtr[1] == 0xC0 &&
+           BufPtr[2] == 0x17 &&
+           BufPtr[3] == 0x0B;
+  }
+
+  /// isNaClRawBitcode - Return true if the given bytes are the magic
+  /// bytes for raw LLVM IR bitcode (without a wrapper).
+  ///
+  inline bool isNaClRawBitcode(const unsigned char *BufPtr,
+                               const unsigned char *BufEnd) {
+    // These bytes sort of have a hidden message, but it's not in
+    // little-endian this time, and it's a little redundant.
+    return BufPtr != BufEnd &&
+           BufPtr[0] == 'B' &&
+           BufPtr[1] == 'C' &&
+           BufPtr[2] == 0xc0 &&
+           BufPtr[3] == 0xde;
+  }
+
+  /// isNaClBitcode - Return true if the given bytes are the magic bytes for
+  /// LLVM IR bitcode, either with or without a wrapper.
+  ///
+  inline bool isNaClBitcode(const unsigned char *BufPtr,
+                        const unsigned char *BufEnd) {
+    return isNaClBitcodeWrapper(BufPtr, BufEnd) ||
+           isNaClRawBitcode(BufPtr, BufEnd);
+  }
+
+  /// SkipNaClBitcodeWrapperHeader - Some systems wrap bc files with a
+  /// special header for padding or other reasons.  The format of this
+  /// header is:
+  ///
+  /// struct bc_header {
+  ///   uint32_t Magic;         // 0x0B17C0DE
+  ///   uint32_t Version;       // Version, currently always 0.
+  ///   uint32_t BitcodeOffset; // Offset to traditional bitcode file.
+  ///   uint32_t BitcodeSize;   // Size of traditional bitcode file.
+  ///   ... potentially other gunk ...

[jvoung (off chromium), 2013/04/29 18:02:08]

Did we put "other gunk" in the wrapper header, to *really* tell the difference
between LLVM bitcode and NaCl files that are frozen?

[Derek Schuff, 2013/04/29 18:25:38]

we probably should. althoughwe might want to just not use the LLVM magic numbers
and wrapper format at all.

[Karl, 2013/04/29 20:44:37]

Not yet. Added TODO to clarify we need to do this.

[Karl, 2013/04/29 20:44:37]

Added TODO for this as well.

+  /// };
+  ///
+  /// This function is called when we find a file with a matching magic number.
+  /// In this case, skip down to the subsection of the file that is actually a
+  /// BC file.
+  /// If 'VerifyBufferSize' is true, check that the buffer is large enough to
+  /// contain the whole bitcode file.
+  inline bool SkipNaClBitcodeWrapperHeader(const unsigned char *&BufPtr,
+                                           const unsigned char *&BufEnd,
+                                           bool VerifyBufferSize) {
+    enum {
+      KnownHeaderSize = 4*4,  // Size of header we read.
+      OffsetField = 2*4,      // Offset in bytes to Offset field.
+      SizeField = 3*4         // Offset in bytes to Size field.
+    };
+
+    // Must contain the header!
+    if (BufEnd-BufPtr < KnownHeaderSize) return true;
+
+    unsigned Offset = ( BufPtr[OffsetField  ]        |
+                       (BufPtr[OffsetField+1] << 8)  |
+                       (BufPtr[OffsetField+2] << 16) |
+                       (BufPtr[OffsetField+3] << 24));
+    unsigned Size   = ( BufPtr[SizeField    ]        |
+                       (BufPtr[SizeField  +1] << 8)  |
+                       (BufPtr[SizeField  +2] << 16) |
+                       (BufPtr[SizeField  +3] << 24));
+
+    // Verify that Offset+Size fits in the file.
+    if (VerifyBufferSize && Offset+Size > unsigned(BufEnd-BufPtr))
+      return true;
+    BufPtr += Offset;
+    BufEnd = BufPtr+Size;
+    return false;
+  }
+
 } // end llvm namespace
 #endif