js/src/jsutil.h

/* -*- 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/. */

/*
 * PR assertion checker.
 */

#ifndef jsutil_h
#define jsutil_h

#include "mozilla/Assertions.h"
#include "mozilla/Compiler.h"
#include "mozilla/GuardObjects.h"
#include "mozilla/PodOperations.h"

#include <limits.h>

#include "js/Utility.h"
#include "js/Value.h"

#define JS_ALWAYS_TRUE(expr)      MOZ_ALWAYS_TRUE(expr)
#define JS_ALWAYS_FALSE(expr)     MOZ_ALWAYS_FALSE(expr)

#if defined(JS_DEBUG)
# define JS_DIAGNOSTICS_ASSERT(expr) MOZ_ASSERT(expr)
#elif defined(JS_CRASH_DIAGNOSTICS)
# define JS_DIAGNOSTICS_ASSERT(expr) do { if (MOZ_UNLIKELY(!(expr))) MOZ_CRASH(); } while(0)
#else
# define JS_DIAGNOSTICS_ASSERT(expr) ((void) 0)
#endif

static MOZ_ALWAYS_INLINE void*
js_memcpy(void* dst_, const void* src_, size_t len)
{
    char* dst = (char*) dst_;
    const char* src = (const char*) src_;
    MOZ_ASSERT_IF(dst >= src, (size_t) (dst - src) >= len);
    MOZ_ASSERT_IF(src >= dst, (size_t) (src - dst) >= len);

    return memcpy(dst, src, len);
}

namespace js {

template <class T>
struct AlignmentTestStruct
{
    char c;
    T t;
};

/* This macro determines the alignment requirements of a type. */
#define JS_ALIGNMENT_OF(t_) \
  (sizeof(js::AlignmentTestStruct<t_>) - sizeof(t_))

template <class T>
class AlignedPtrAndFlag
{
    uintptr_t bits;

  public:
    AlignedPtrAndFlag(T* t, bool aFlag) {
        MOZ_ASSERT((uintptr_t(t) & 1) == 0);
        bits = uintptr_t(t) | uintptr_t(aFlag);
    }

    T* ptr() const {
        return (T*)(bits & ~uintptr_t(1));
    }

    bool flag() const {
        return (bits & 1) != 0;
    }

    void setPtr(T* t) {
        MOZ_ASSERT((uintptr_t(t) & 1) == 0);
        bits = uintptr_t(t) | uintptr_t(flag());
    }

    void setFlag() {
        bits |= 1;
    }

    void unsetFlag() {
        bits &= ~uintptr_t(1);
    }

    void set(T* t, bool aFlag) {
        MOZ_ASSERT((uintptr_t(t) & 1) == 0);
        bits = uintptr_t(t) | aFlag;
    }
};

template <class T>
static inline void
Reverse(T* beg, T* end)
{
    while (beg != end) {
        if (--end == beg)
            return;
        T tmp = *beg;
        *beg = *end;
        *end = tmp;
        ++beg;
    }
}

template <class T>
static inline T*
Find(T* beg, T* end, const T& v)
{
    for (T* p = beg; p != end; ++p) {
        if (*p == v)
            return p;
    }
    return end;
}

template <class Container>
static inline typename Container::ElementType*
Find(Container& c, const typename Container::ElementType& v)
{
    return Find(c.begin(), c.end(), v);
}

template <typename InputIterT, typename CallableT>
void
ForEach(InputIterT begin, InputIterT end, CallableT f)
{
    for (; begin != end; ++begin)
        f(*begin);
}

template <class T>
static inline T
Min(T t1, T t2)
{
    return t1 < t2 ? t1 : t2;
}

template <class T>
static inline T
Max(T t1, T t2)
{
    return t1 > t2 ? t1 : t2;
}

/* Allows a const variable to be initialized after its declaration. */
template <class T>
static T&
InitConst(const T& t)
{
    return const_cast<T&>(t);
}

template <class T, class U>
MOZ_ALWAYS_INLINE T&
ImplicitCast(U& u)
{
    T& t = u;
    return t;
}

template<typename T>
class MOZ_RAII AutoScopedAssign
{
  public:
    AutoScopedAssign(T* addr, const T& value
                     MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
        : addr_(addr), old(*addr_)
    {
        MOZ_GUARD_OBJECT_NOTIFIER_INIT;
        *addr_ = value;
    }

    ~AutoScopedAssign() { *addr_ = old; }

  private:
    MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
    T* addr_;
    T old;
};

template <typename T>
static inline bool
IsPowerOfTwo(T t)
{
    return t && !(t & (t - 1));
}

template <typename T, typename U>
static inline U
ComputeByteAlignment(T bytes, U alignment)
{
    MOZ_ASSERT(IsPowerOfTwo(alignment));
    return (alignment - (bytes % alignment)) % alignment;
}

template <typename T, typename U>
static inline T
AlignBytes(T bytes, U alignment)
{
    return bytes + ComputeByteAlignment(bytes, alignment);
}

static MOZ_ALWAYS_INLINE size_t
UnsignedPtrDiff(const void* bigger, const void* smaller)
{
    return size_t(bigger) - size_t(smaller);
}

/*****************************************************************************/

/* A bit array is an array of bits represented by an array of words (size_t). */

static const size_t BitArrayElementBits = sizeof(size_t) * CHAR_BIT;

static inline unsigned
NumWordsForBitArrayOfLength(size_t length)
{
    return (length + (BitArrayElementBits - 1)) / BitArrayElementBits;
}

static inline unsigned
BitArrayIndexToWordIndex(size_t length, size_t bitIndex)
{
    unsigned wordIndex = bitIndex / BitArrayElementBits;
    MOZ_ASSERT(wordIndex < length);
    return wordIndex;
}

static inline size_t
BitArrayIndexToWordMask(size_t i)
{
    return size_t(1) << (i % BitArrayElementBits);
}

static inline bool
IsBitArrayElementSet(size_t* array, size_t length, size_t i)
{
    return array[BitArrayIndexToWordIndex(length, i)] & BitArrayIndexToWordMask(i);
}

static inline bool
IsAnyBitArrayElementSet(size_t* array, size_t length)
{
    unsigned numWords = NumWordsForBitArrayOfLength(length);
    for (unsigned i = 0; i < numWords; ++i) {
        if (array[i])
            return true;
    }
    return false;
}

static inline void
SetBitArrayElement(size_t* array, size_t length, size_t i)
{
    array[BitArrayIndexToWordIndex(length, i)] |= BitArrayIndexToWordMask(i);
}

static inline void
ClearBitArrayElement(size_t* array, size_t length, size_t i)
{
    array[BitArrayIndexToWordIndex(length, i)] &= ~BitArrayIndexToWordMask(i);
}

static inline void
ClearAllBitArrayElements(size_t* array, size_t length)
{
    for (unsigned i = 0; i < length; ++i)
        array[i] = 0;
}

}  /* namespace js */

namespace mozilla {

/**
 * Set the first |aNElem| T elements in |aDst| to |aSrc|.
 */
template<typename T>
static MOZ_ALWAYS_INLINE void
PodSet(T* aDst, T aSrc, size_t aNElem)
{
    for (const T* dstend = aDst + aNElem; aDst < dstend; ++aDst)
        *aDst = aSrc;
}

} /* namespace mozilla */

/*
 * Patterns used by SpiderMonkey to overwrite unused memory. If you are
 * accessing an object with one of these pattern, you probably have a dangling
 * pointer. These values should be odd, see the comment in IsThingPoisoned.
 *
 * Note: new patterns should also be added to the array in IsThingPoisoned!
 */
#define JS_FRESH_NURSERY_PATTERN 0x2F
#define JS_SWEPT_NURSERY_PATTERN 0x2B
#define JS_ALLOCATED_NURSERY_PATTERN 0x2D
#define JS_FRESH_TENURED_PATTERN 0x4F
#define JS_MOVED_TENURED_PATTERN 0x49
#define JS_SWEPT_TENURED_PATTERN 0x4B
#define JS_ALLOCATED_TENURED_PATTERN 0x4D
#define JS_FREED_HEAP_PTR_PATTERN 0x6B

/*
 * Ensure JS_SWEPT_CODE_PATTERN is a byte pattern that will crash immediately
 * when executed, so either an undefined instruction or an instruction that's
 * illegal in user mode.
 */
#if defined(JS_CODEGEN_X86) || defined(JS_CODEGEN_X64) || defined(JS_CODEGEN_NONE)
# define JS_SWEPT_CODE_PATTERN 0xED // IN instruction, crashes in user mode.
#elif defined(JS_CODEGEN_ARM) || defined(JS_CODEGEN_ARM64)
# define JS_SWEPT_CODE_PATTERN 0xA3 // undefined instruction
#elif defined(JS_CODEGEN_MIPS32) || defined(JS_CODEGEN_MIPS64)
# define JS_SWEPT_CODE_PATTERN 0x01 // undefined instruction
#else
# error "JS_SWEPT_CODE_PATTERN not defined for this platform"
#endif

static inline void*
Poison(void* ptr, uint8_t value, size_t num)
{
    static bool disablePoison = bool(getenv("JSGC_DISABLE_POISONING"));
    if (disablePoison)
        return ptr;

    // Without a valid Value tag, a poisoned Value may look like a valid
    // floating point number. To ensure that we crash more readily when
    // observing a poisoned Value, we make the poison an invalid ObjectValue.
    // Unfortunately, this adds about 2% more overhead, so we can only enable
    // it in debug.
#if defined(DEBUG)
    uintptr_t obj;
    memset(&obj, value, sizeof(obj));
# if defined(JS_PUNBOX64)
    obj = obj & ((uintptr_t(1) << JSVAL_TAG_SHIFT) - 1);
# endif
    const jsval_layout layout = OBJECT_TO_JSVAL_IMPL((JSObject*)obj);

    size_t value_count = num / sizeof(jsval_layout);
    size_t byte_count = num % sizeof(jsval_layout);
    mozilla::PodSet((jsval_layout*)ptr, layout, value_count);
    if (byte_count) {
        uint8_t* bytes = static_cast<uint8_t*>(ptr);
        uint8_t* end = bytes + num;
        mozilla::PodSet(end - byte_count, value, byte_count);
    }
#else // !DEBUG
    memset(ptr, value, num);
#endif // !DEBUG
    return ptr;
}

/* Crash diagnostics by default in debug and on nightly channel. */
#if (defined(DEBUG) || defined(NIGHTLY_BUILD)) && !defined(MOZ_ASAN)
# define JS_CRASH_DIAGNOSTICS 1
#endif

/* Enable poisoning in crash-diagnostics and zeal builds. */
#if defined(JS_CRASH_DIAGNOSTICS) || defined(JS_GC_ZEAL)
# define JS_POISON(p, val, size) Poison(p, val, size)
#else
# define JS_POISON(p, val, size) ((void) 0)
#endif

/* Enable even more poisoning in purely debug builds. */
#if defined(DEBUG)
# define JS_EXTRA_POISON(p, val, size) Poison(p, val, size)
#else
# define JS_EXTRA_POISON(p, val, size) ((void) 0)
#endif

/* Basic stats */
#ifdef DEBUG
# define JS_BASIC_STATS 1
#endif
#ifdef JS_BASIC_STATS
# include <stdio.h>
typedef struct JSBasicStats {
    uint32_t    num;
    uint32_t    max;
    double      sum;
    double      sqsum;
    uint32_t    logscale;           /* logarithmic scale: 0 (linear), 2, 10 */
    uint32_t    hist[11];
} JSBasicStats;
# define JS_INIT_STATIC_BASIC_STATS  {0,0,0,0,0,{0,0,0,0,0,0,0,0,0,0,0}}
# define JS_BASIC_STATS_INIT(bs)     memset((bs), 0, sizeof(JSBasicStats))
# define JS_BASIC_STATS_ACCUM(bs,val)                                         \
    JS_BasicStatsAccum(bs, val)
# define JS_MeanAndStdDevBS(bs,sigma)                                         \
    JS_MeanAndStdDev((bs)->num, (bs)->sum, (bs)->sqsum, sigma)
extern void
JS_BasicStatsAccum(JSBasicStats* bs, uint32_t val);
extern double
JS_MeanAndStdDev(uint32_t num, double sum, double sqsum, double* sigma);
extern void
JS_DumpBasicStats(JSBasicStats* bs, const char* title, FILE* fp);
extern void
JS_DumpHistogram(JSBasicStats* bs, FILE* fp);
#else
# define JS_BASIC_STATS_ACCUM(bs,val)
#endif

/* A jsbitmap_t is a long integer that can be used for bitmaps. */
typedef size_t jsbitmap;
#define JS_BITMAP_NBITS (sizeof(jsbitmap) * CHAR_BIT)
#define JS_TEST_BIT(_map,_bit)  ((_map)[(_bit)/JS_BITMAP_NBITS] &             \
                                 (jsbitmap(1)<<((_bit)%JS_BITMAP_NBITS)))
#define JS_SET_BIT(_map,_bit)   ((_map)[(_bit)/JS_BITMAP_NBITS] |=            \
                                 (jsbitmap(1)<<((_bit)%JS_BITMAP_NBITS)))
#define JS_CLEAR_BIT(_map,_bit) ((_map)[(_bit)/JS_BITMAP_NBITS] &=            \
                                 ~(jsbitmap(1)<<((_bit)%JS_BITMAP_NBITS)))

/* Wrapper for various macros to stop warnings coming from their expansions. */
#if defined(__clang__)
# define JS_SILENCE_UNUSED_VALUE_IN_EXPR(expr)                                \
    JS_BEGIN_MACRO                                                            \
        _Pragma("clang diagnostic push")                                      \
        /* If these _Pragmas cause warnings for you, try disabling ccache. */ \
        _Pragma("clang diagnostic ignored \"-Wunused-value\"")                \
        { expr; }                                                             \
        _Pragma("clang diagnostic pop")                                       \
    JS_END_MACRO
#elif MOZ_IS_GCC

# define JS_SILENCE_UNUSED_VALUE_IN_EXPR(expr)                                \
    JS_BEGIN_MACRO                                                            \
        _Pragma("GCC diagnostic push")                                        \
        _Pragma("GCC diagnostic ignored \"-Wunused-but-set-variable\"")       \
        expr;                                                                 \
        _Pragma("GCC diagnostic pop")                                         \
    JS_END_MACRO
#endif

#if !defined(JS_SILENCE_UNUSED_VALUE_IN_EXPR)
# define JS_SILENCE_UNUSED_VALUE_IN_EXPR(expr)                                \
    JS_BEGIN_MACRO                                                            \
        expr;                                                                 \
    JS_END_MACRO
#endif

#endif /* jsutil_h */