protobuf/upb/pb/decoder.int.h

/*
 * upb - a minimalist implementation of protocol buffers.
 *
 * Copyright (c) 2009-2014 Google Inc.  See LICENSE for details.
 * Author: Josh Haberman <jhaberman@gmail.com>
 *
 * Internal-only definitions for the decoder.
 */

#ifndef UPB_DECODER_INT_H_
#define UPB_DECODER_INT_H_

#include <stdlib.h>
#include "upb/def.h"
#include "upb/handlers.h"
#include "upb/pb/decoder.h"
#include "upb/sink.h"
#include "upb/table.int.h"

// Opcode definitions.  The canonical meaning of each opcode is its
// implementation in the interpreter (the JIT is written to match this).
//
// All instructions have the opcode in the low byte.
// Instruction format for most instructions is:
//
// +-------------------+--------+
// |     arg (24)      | op (8) |
// +-------------------+--------+
//
// Exceptions are indicated below.  A few opcodes are multi-word.
typedef enum {
  // Opcodes 1-8, 13, 15-18 parse their respective descriptor types.
  // Arg for all of these is the upb selector for this field.
#define T(type) OP_PARSE_ ## type = UPB_DESCRIPTOR_TYPE_ ## type
  T(DOUBLE), T(FLOAT), T(INT64), T(UINT64), T(INT32), T(FIXED64), T(FIXED32),
  T(BOOL), T(UINT32), T(SFIXED32), T(SFIXED64), T(SINT32), T(SINT64),
#undef T
  OP_STARTMSG       = 9,   // No arg.
  OP_ENDMSG         = 10,  // No arg.
  OP_STARTSEQ       = 11,
  OP_ENDSEQ         = 12,
  OP_STARTSUBMSG    = 14,
  OP_ENDSUBMSG      = 19,
  OP_STARTSTR       = 20,
  OP_STRING         = 21,
  OP_ENDSTR         = 22,

  OP_PUSHTAGDELIM   = 23,  // No arg.
  OP_PUSHLENDELIM   = 24,  // No arg.
  OP_POP            = 25,  // No arg.
  OP_SETDELIM       = 26,  // No arg.
  OP_SETBIGGROUPNUM = 27,  // two words: | unused (24) | opc || groupnum (32) |
  OP_CHECKDELIM     = 28,
  OP_CALL           = 29,
  OP_RET            = 30,
  OP_BRANCH         = 31,

  // Different opcodes depending on how many bytes expected.
  OP_TAG1           = 32,  // | expected tag (16) | jump target (8) | opc (8) |
  OP_TAG2           = 33,  // | expected tag (16) | jump target (8) | opc (8) |
  OP_TAGN           = 34,  // three words:
                           //   | unused (16) | jump target(8) | opc (8) |
                           //   |           expected tag 1 (32)          |
                           //   |           expected tag 2 (32)          |

  OP_SETDISPATCH    = 35,  // N words:
                           //   | unused (24)         | opc |
                           //   | upb_inttable* (32 or 64)  |

  OP_DISPATCH       = 36,  // No arg.

  OP_HALT           = 37,  // No arg.
} opcode;

#define OP_MAX OP_HALT

UPB_INLINE opcode getop(uint32_t instr) { return instr & 0xff; }

// Method group; represents a set of decoder methods that had their code
// emitted together, and must therefore be freed together.  Immutable once
// created.  It is possible we may want to expose this to users at some point.
//
// Overall ownership of Decoder objects looks like this:
//
//                +----------+
//                |          | <---> DecoderMethod
//                | method   |
// CodeCache ---> |  group   | <---> DecoderMethod
//                |          |
//                | (mgroup) | <---> DecoderMethod
//                +----------+
typedef struct {
  upb_refcounted base;

  // Maps upb_msgdef/upb_handlers -> upb_pbdecodermethod.  We own refs on the
  // methods.
  upb_inttable methods;

  // When we add the ability to link to previously existing mgroups, we'll
  // need an array of mgroups we reference here, and own refs on them.

  // The bytecode for our methods, if any exists.  Owned by us.
  uint32_t *bytecode;
  uint32_t *bytecode_end;

#ifdef UPB_USE_JIT_X64
  // JIT-generated machine code, if any.
  upb_string_handlerfunc *jit_code;
  // The size of the jit_code (required to munmap()).
  size_t jit_size;
  char *debug_info;
  void *dl;
#endif
} mgroup;

// The maximum that any submessages can be nested.  Matches proto2's limit.
// This specifies the size of the decoder's statically-sized array and therefore
// setting it high will cause the upb::pb::Decoder object to be larger.
//
// If necessary we can add a runtime-settable property to Decoder that allow
// this to be larger than the compile-time setting, but this would add
// complexity, particularly since we would have to decide how/if to give users
// the ability to set a custom memory allocation function.
#define UPB_DECODER_MAX_NESTING 64

// Internal-only struct used by the decoder.
typedef struct {
  // Space optimization note: we store two pointers here that the JIT
  // doesn't need at all; the upb_handlers* inside the sink and
  // the dispatch table pointer.  We can optimze so that the JIT uses
  // smaller stack frames than the interpreter.  The only thing we need
  // to guarantee is that the fallback routines can find end_ofs.
  upb_sink sink;

  // The absolute stream offset of the end-of-frame delimiter.
  // Non-delimited frames (groups and non-packed repeated fields) reuse the
  // delimiter of their parent, even though the frame may not end there.
  //
  // NOTE: the JIT stores a slightly different value here for non-top frames.
  // It stores the value relative to the end of the enclosed message.  But the
  // top frame is still stored the same way, which is important for ensuring
  // that calls from the JIT into C work correctly.
  uint64_t end_ofs;
  const uint32_t *base;

  // 0 indicates a length-delimited field.
  // A positive number indicates a known group.
  // A negative number indicates an unknown group.
  int32_t groupnum;
  upb_inttable *dispatch;  // Not used by the JIT.
} upb_pbdecoder_frame;

struct upb_pbdecoder {
  upb_env *env;

  // Our input sink.
  upb_bytessink input_;

  // The decoder method we are parsing with (owned).
  const upb_pbdecodermethod *method_;

  size_t call_len;
  const uint32_t *pc, *last;

  // Current input buffer and its stream offset.
  const char *buf, *ptr, *end, *checkpoint;

  // End of the delimited region, relative to ptr, or NULL if not in this buf.
  const char *delim_end;

  // End of the delimited region, relative to ptr, or end if not in this buf.
  const char *data_end;

  // Overall stream offset of "buf."
  uint64_t bufstart_ofs;

  // Buffer for residual bytes not parsed from the previous buffer.
  // The maximum number of residual bytes we require is 12; a five-byte
  // unknown tag plus an eight-byte value, less one because the value
  // is only a partial value.
  char residual[12];
  char *residual_end;

  // Stores the user buffer passed to our decode function.
  const char *buf_param;
  size_t size_param;
  const upb_bufhandle *handle;

  // Our internal stack.
  upb_pbdecoder_frame *stack, *top, *limit;
  const uint32_t **callstack;
  size_t stack_size;

  upb_status *status;

#ifdef UPB_USE_JIT_X64
  // Used momentarily by the generated code to store a value while a user
  // function is called.
  uint32_t tmp_len;

  const void *saved_rsp;
#endif
};

// Decoder entry points; used as handlers.
void *upb_pbdecoder_startbc(void *closure, const void *pc, size_t size_hint);
void *upb_pbdecoder_startjit(void *closure, const void *hd, size_t size_hint);
size_t upb_pbdecoder_decode(void *closure, const void *hd, const char *buf,
                            size_t size, const upb_bufhandle *handle);
bool upb_pbdecoder_end(void *closure, const void *handler_data);

// Decoder-internal functions that the JIT calls to handle fallback paths.
int32_t upb_pbdecoder_resume(upb_pbdecoder *d, void *p, const char *buf,
                             size_t size, const upb_bufhandle *handle);
size_t upb_pbdecoder_suspend(upb_pbdecoder *d);
int32_t upb_pbdecoder_skipunknown(upb_pbdecoder *d, int32_t fieldnum,
                                  uint8_t wire_type);
int32_t upb_pbdecoder_checktag_slow(upb_pbdecoder *d, uint64_t expected);
int32_t upb_pbdecoder_decode_varint_slow(upb_pbdecoder *d, uint64_t *u64);
int32_t upb_pbdecoder_decode_f32(upb_pbdecoder *d, uint32_t *u32);
int32_t upb_pbdecoder_decode_f64(upb_pbdecoder *d, uint64_t *u64);
void upb_pbdecoder_seterr(upb_pbdecoder *d, const char *msg);

// Error messages that are shared between the bytecode and JIT decoders.
extern const char *kPbDecoderStackOverflow;

// Access to decoderplan members needed by the decoder.
const char *upb_pbdecoder_getopname(unsigned int op);

// JIT codegen entry point.
void upb_pbdecoder_jit(mgroup *group);
void upb_pbdecoder_freejit(mgroup *group);

// A special label that means "do field dispatch for this message and branch to
// wherever that takes you."
#define LABEL_DISPATCH 0

// A special slot in the dispatch table that stores the epilogue (ENDMSG and/or
// RET) for branching to when we find an appropriate ENDGROUP tag.
#define DISPATCH_ENDMSG 0

// It's important to use this invalid wire type instead of 0 (which is a valid
// wire type).
#define NO_WIRE_TYPE 0xff

// The dispatch table layout is:
//   [field number] -> [ 48-bit offset ][ 8-bit wt2 ][ 8-bit wt1 ]
//
// If wt1 matches, jump to the 48-bit offset.  If wt2 matches, lookup
// (UPB_MAX_FIELDNUMBER + fieldnum) and jump there.
//
// We need two wire types because of packed/non-packed compatibility.  A
// primitive repeated field can use either wire type and be valid.  While we
// could key the table on fieldnum+wiretype, the table would be 8x sparser.
//
// Storing two wire types in the primary value allows us to quickly rule out
// the second wire type without needing to do a separate lookup (this case is
// less common than an unknown field).
UPB_INLINE uint64_t upb_pbdecoder_packdispatch(uint64_t ofs, uint8_t wt1,
                                               uint8_t wt2) {
  return (ofs << 16) | (wt2 << 8) | wt1;
}

UPB_INLINE void upb_pbdecoder_unpackdispatch(uint64_t dispatch, uint64_t *ofs,
                                             uint8_t *wt1, uint8_t *wt2) {
  *wt1 = (uint8_t)dispatch;
  *wt2 = (uint8_t)(dispatch >> 8);
  *ofs = dispatch >> 16;
}

// All of the functions in decoder.c that return int32_t return values according
// to the following scheme:
//   1. negative values indicate a return code from the following list.
//   2. positive values indicate that error or end of buffer was hit, and
//      that the decode function should immediately return the given value
//      (the decoder state has already been suspended and is ready to be
//      resumed).
#define DECODE_OK -1
#define DECODE_MISMATCH -2  // Used only from checktag_slow().
#define DECODE_ENDGROUP -3  // Used only from checkunknown().

#define CHECK_RETURN(x) { int32_t ret = x; if (ret >= 0) return ret; }

#endif  // UPB_DECODER_INT_H_