js/src/vm/Xdr.h
author Carsten "Tomcat" Book <cbook@mozilla.com>
Thu, 22 Jan 2015 14:30:51 +0100
changeset 225116 86f9d0128ccf397ba4b09c1f5e0524ad1a77e2e6
parent 223947 f7498b5f244b58f9a23cb736a5cb531a2ea476a7
child 225451 4ba8480c860809190ebcb29cf17b6cbb4bfe9dca
permissions -rw-r--r--
merge mozilla-inbound to mozilla-central a=merge

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * vim: set ts=8 sts=4 et sw=4 tw=99:
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef vm_Xdr_h
#define vm_Xdr_h

#include "mozilla/Endian.h"
#include "mozilla/TypeTraits.h"

#include "jsatom.h"
#include "jsfriendapi.h"

namespace js {

/*
 * Bytecode version number. Increment the subtrahend whenever JS bytecode
 * changes incompatibly.
 *
 * This version number is XDR'd near the front of xdr bytecode and aborts
 * deserialization if there is a mismatch between the current and saved
 * versions.  If deserialization fails, the data should be invalidated if
 * possible.
 *
 * When you change this, run make_opcode_doc.py and copy the new output into
 * this wiki page:
 *
 *  https://developer.mozilla.org/en-US/docs/SpiderMonkey/Internals/Bytecode
 *
 * === GREETINGS, FELLOW SUBTRAHEND INCREMENTER! ===
 * For the time being, please increment the subtrahend by 2 each time it
 * changes, because we have two flavors of bytecode: with JSOP_SYMBOL (in
 * Nightly) and without (all others).  FIXME: Bug 1066322 - Enable ES6 symbols
 * in all builds.
 */
static const uint32_t XDR_BYTECODE_VERSION_SUBTRAHEND = 228;
static_assert(XDR_BYTECODE_VERSION_SUBTRAHEND % 2 == 0, "see the comment above");
static const uint32_t XDR_BYTECODE_VERSION =
    uint32_t(0xb973c0de - (XDR_BYTECODE_VERSION_SUBTRAHEND
#ifdef JS_HAS_SYMBOLS
                                                           + 1
#endif
                                                              ));

static_assert(JSErr_Limit == 366,
              "GREETINGS, POTENTIAL SUBTRAHEND INCREMENTER! If you added or "
              "removed MSG_DEFs from js.msg, you should increment "
              "XDR_BYTECODE_VERSION_SUBTRAHEND and update this assertion's "
              "expected JSErr_Limit value.");

class XDRBuffer {
  public:
    explicit XDRBuffer(JSContext *cx)
      : context(cx), base(nullptr), cursor(nullptr), limit(nullptr) { }

    JSContext *cx() const {
        return context;
    }

    void *getData(uint32_t *lengthp) const {
        MOZ_ASSERT(size_t(cursor - base) <= size_t(UINT32_MAX));
        *lengthp = uint32_t(cursor - base);
        return base;
    }

    void setData(const void *data, uint32_t length) {
        base = static_cast<uint8_t *>(const_cast<void *>(data));
        cursor = base;
        limit = base + length;
    }

    const uint8_t *read(size_t n) {
        MOZ_ASSERT(n <= size_t(limit - cursor));
        uint8_t *ptr = cursor;
        cursor += n;
        return ptr;
    }

    const char *readCString() {
        char *ptr = reinterpret_cast<char *>(cursor);
        cursor = reinterpret_cast<uint8_t *>(strchr(ptr, '\0')) + 1;
        MOZ_ASSERT(base < cursor);
        MOZ_ASSERT(cursor <= limit);
        return ptr;
    }

    uint8_t *write(size_t n) {
        if (n > size_t(limit - cursor)) {
            if (!grow(n))
                return nullptr;
        }
        uint8_t *ptr = cursor;
        cursor += n;
        return ptr;
    }

    static bool isUint32Overflow(size_t n) {
        return size_t(-1) > size_t(UINT32_MAX) && n > size_t(UINT32_MAX);
    }

    void freeBuffer();

  private:
    bool grow(size_t n);

    JSContext   *const context;
    uint8_t     *base;
    uint8_t     *cursor;
    uint8_t     *limit;
};

/*
 * XDR serialization state.  All data is encoded in little endian.
 */
template <XDRMode mode>
class XDRState {
  public:
    XDRBuffer buf;

  protected:
    explicit XDRState(JSContext *cx)
      : buf(cx) { }

  public:
    JSContext *cx() const {
        return buf.cx();
    }

    bool codeUint8(uint8_t *n) {
        if (mode == XDR_ENCODE) {
            uint8_t *ptr = buf.write(sizeof *n);
            if (!ptr)
                return false;
            *ptr = *n;
        } else {
            *n = *buf.read(sizeof *n);
        }
        return true;
    }

    bool codeUint16(uint16_t *n) {
        if (mode == XDR_ENCODE) {
            uint8_t *ptr = buf.write(sizeof *n);
            if (!ptr)
                return false;
            mozilla::LittleEndian::writeUint16(ptr, *n);
        } else {
            const uint8_t *ptr = buf.read(sizeof *n);
            *n = mozilla::LittleEndian::readUint16(ptr);
        }
        return true;
    }

    bool codeUint32(uint32_t *n) {
        if (mode == XDR_ENCODE) {
            uint8_t *ptr = buf.write(sizeof *n);
            if (!ptr)
                return false;
            mozilla::LittleEndian::writeUint32(ptr, *n);
        } else {
            const uint8_t *ptr = buf.read(sizeof *n);
            *n = mozilla::LittleEndian::readUint32(ptr);
        }
        return true;
    }

    bool codeUint64(uint64_t *n) {
        if (mode == XDR_ENCODE) {
            uint8_t *ptr = buf.write(sizeof(*n));
            if (!ptr)
                return false;
            mozilla::LittleEndian::writeUint64(ptr, *n);
        } else {
            const uint8_t *ptr = buf.read(sizeof(*n));
            *n = mozilla::LittleEndian::readUint64(ptr);
        }
        return true;
    }

    /*
     * Use SFINAE to refuse any specialization which is not an enum.  Uses of
     * this function do not have to specialize the type of the enumerated field
     * as C++ will extract the parameterized from the argument list.
     */
    template <typename T>
    bool codeEnum32(T *val, typename mozilla::EnableIf<mozilla::IsEnum<T>::value, T>::Type * = NULL)
    {
        uint32_t tmp;
        if (mode == XDR_ENCODE)
            tmp = *val;
        if (!codeUint32(&tmp))
            return false;
        if (mode == XDR_DECODE)
            *val = T(tmp);
        return true;
    }

    bool codeDouble(double *dp) {
        union DoublePun {
            double d;
            uint64_t u;
        } pun;
        if (mode == XDR_ENCODE)
            pun.d = *dp;
        if (!codeUint64(&pun.u))
            return false;
        if (mode == XDR_DECODE)
            *dp = pun.d;
        return true;
    }

    bool codeBytes(void *bytes, size_t len) {
        if (mode == XDR_ENCODE) {
            uint8_t *ptr = buf.write(len);
            if (!ptr)
                return false;
            memcpy(ptr, bytes, len);
        } else {
            memcpy(bytes, buf.read(len), len);
        }
        return true;
    }

    /*
     * During encoding the string is written into the buffer together with its
     * terminating '\0'. During decoding the method returns a pointer into the
     * decoding buffer and the caller must copy the string if it will outlive
     * the decoding buffer.
     */
    bool codeCString(const char **sp) {
        if (mode == XDR_ENCODE) {
            size_t n = strlen(*sp) + 1;
            uint8_t *ptr = buf.write(n);
            if (!ptr)
                return false;
            memcpy(ptr, *sp, n);
        } else {
            *sp = buf.readCString();
        }
        return true;
    }

    bool codeChars(const JS::Latin1Char *chars, size_t nchars);
    bool codeChars(char16_t *chars, size_t nchars);

    bool codeFunction(JS::MutableHandleFunction objp);
    bool codeScript(MutableHandleScript scriptp);
    bool codeConstValue(MutableHandleValue vp);
};

class XDREncoder : public XDRState<XDR_ENCODE> {
  public:
    explicit XDREncoder(JSContext *cx)
      : XDRState<XDR_ENCODE>(cx) {
    }

    ~XDREncoder() {
        buf.freeBuffer();
    }

    const void *getData(uint32_t *lengthp) const {
        return buf.getData(lengthp);
    }

    void *forgetData(uint32_t *lengthp) {
        void *data = buf.getData(lengthp);
        buf.setData(nullptr, 0);
        return data;
    }
};

class XDRDecoder : public XDRState<XDR_DECODE> {
  public:
    XDRDecoder(JSContext *cx, const void *data, uint32_t length);

};

} /* namespace js */

#endif /* vm_Xdr_h */