Source/JavaScriptCore/heap/GCMemoryOperations.h

/*
 * Copyright (C) 2016-2018 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#pragma once

#include "CPU.h"
#include "JSCJSValue.h"

namespace JSC {

// We use these memory operations when modifying memory that might be scanned by the concurrent collector.
// We don't call the default operations because they're not guaranteed to store to memory in eight byte aligned
// chunks. If we happened to fall into the system's normal byte copy loop, we may see a torn JSValue in the
// concurrent collector.

constexpr size_t smallCutoff = 30 * 8;
constexpr size_t mediumCutoff = 4 * 1024;

// This is a forwards loop so gcSafeMemmove can rely on the direction. 
template <typename T>
ALWAYS_INLINE void gcSafeMemcpy(T* dst, T* src, size_t bytes)
{
    static_assert(sizeof(T) == sizeof(JSValue));
    RELEASE_ASSERT(bytes % 8 == 0);

#if USE(JSVALUE64)

    auto slowPathForwardMemcpy = [&] {
        size_t count = bytes / 8;
        for (unsigned i = 0; i < count; ++i)
            bitwise_cast<volatile uint64_t*>(dst)[i] = bitwise_cast<volatile uint64_t*>(src)[i];
    };

#if COMPILER(GCC_COMPATIBLE) && (CPU(X86_64) || CPU(ARM64))
    if (bytes <= smallCutoff)
        slowPathForwardMemcpy();
    else if (isARM64() || bytes <= mediumCutoff) {
#if CPU(X86_64)
        size_t alignedBytes = (bytes / 64) * 64;
        size_t tmp;
        size_t offset = 0;
        asm volatile(
            ".balign 32\t\n"
            "1:\t\n"
            "cmpq %q[offset], %q[alignedBytes]\t\n"
            "je 2f\t\n"
            "movups (%q[src], %q[offset], 1), %%xmm0\t\n"
            "movups 16(%q[src], %q[offset], 1), %%xmm1\t\n"
            "movups 32(%q[src], %q[offset], 1), %%xmm2\t\n"
            "movups 48(%q[src], %q[offset], 1), %%xmm3\t\n"
            "movups %%xmm0, (%q[dst], %q[offset], 1)\t\n"
            "movups %%xmm1, 16(%q[dst], %q[offset], 1)\t\n"
            "movups %%xmm2, 32(%q[dst], %q[offset], 1)\t\n"
            "movups %%xmm3, 48(%q[dst], %q[offset], 1)\t\n"
            "addq $64, %q[offset]\t\n"
            "jmp 1b\t\n"

            "2:\t\n"
            "cmpq %q[offset], %q[bytes]\t\n"
            "je 3f\t\n"
            "movq (%q[src], %q[offset], 1), %q[tmp]\t\n"
            "movq %q[tmp], (%q[dst], %q[offset], 1)\t\n"
            "addq $8, %q[offset]\t\n"
            "jmp 2b\t\n"

            "3:\t\n"

            : [alignedBytes] "+r" (alignedBytes), [bytes] "+r" (bytes), [tmp] "+r" (tmp), [offset] "+r" (offset), [dst] "+r" (dst), [src] "+r" (src)
            :
            : "xmm0", "xmm1", "xmm2", "xmm3", "memory", "cc"
        );
#elif CPU(ARM64)
        uint64_t alignedBytes = (static_cast<uint64_t>(bytes) / 16) * 16;
        size_t offset = 0;

        uint64_t dstPtr = static_cast<uint64_t>(bitwise_cast<uintptr_t>(dst));
        uint64_t srcPtr = static_cast<uint64_t>(bitwise_cast<uintptr_t>(src));

        asm volatile(
            "1:\t\n"
            "cmp %x[offset], %x[alignedBytes]\t\n"
            "b.eq 2f\t\n"
            "ldr q0, [%x[srcPtr], %x[offset]]\t\n"
            "str q0, [%x[dstPtr], %x[offset]]\t\n"
            "add %x[offset], %x[offset], #0x10\t\n"
            "b 1b\t\n"

            "2:\t\n"
            "cmp %x[offset], %x[bytes]\t\n"
            "b.eq 3f\t\n"
            "ldr d0, [%x[srcPtr], %x[offset]]\t\n"
            "str d0, [%x[dstPtr], %x[offset]]\t\n"
            "add %x[offset], %x[offset], #0x8\t\n"
            "b 2b\t\n"

            "3:\t\n"

            : [alignedBytes] "+r" (alignedBytes), [bytes] "+r" (bytes), [offset] "+r" (offset), [dstPtr] "+r" (dstPtr), [srcPtr] "+r" (srcPtr)
            :
            : "d0", "d1", "memory"
        );
#endif // CPU(X86_64)
    } else {
        RELEASE_ASSERT(isX86_64());
#if CPU(X86_64)
        size_t count = bytes / 8;
        asm volatile(
            ".balign 16\t\n"
            "cld\t\n"
            "rep movsq\t\n"
            : "+D" (dst), "+S" (src), "+c" (count)
            :
            : "memory");
#endif // CPU(X86_64)
    }
#else
    slowPathForwardMemcpy();
#endif // COMPILER(GCC_COMPATIBLE) && (CPU(X86_64) || CPU(ARM64))
#else
    memcpy(dst, src, bytes);
#endif // USE(JSVALUE64)
}

template <typename T>
ALWAYS_INLINE void gcSafeMemmove(T* dst, T* src, size_t bytes)
{
    static_assert(sizeof(T) == sizeof(JSValue));
    RELEASE_ASSERT(bytes % 8 == 0);
#if USE(JSVALUE64)
    if (bitwise_cast<uintptr_t>(src) >= bitwise_cast<uintptr_t>(dst)) {
        // This is written to do a forwards loop, so calling it is ok.
        gcSafeMemcpy(dst, src, bytes);
        return;
    }

    if ((static_cast<uint64_t>(bitwise_cast<uintptr_t>(src)) + static_cast<uint64_t>(bytes)) <= static_cast<uint64_t>(bitwise_cast<uintptr_t>(dst))) {
        gcSafeMemcpy(dst, src, bytes);
        return;
    }

    auto slowPathBackwardsMemmove = [&] {
        size_t count = bytes / 8;
        for (size_t i = count; i--; )
            bitwise_cast<volatile uint64_t*>(dst)[i] = bitwise_cast<volatile uint64_t*>(src)[i];
    };

#if COMPILER(GCC_COMPATIBLE) && (CPU(X86_64) || CPU(ARM64))
    if (bytes <= smallCutoff)
        slowPathBackwardsMemmove();
    else {
#if CPU(X86_64)
        size_t alignedBytes = (bytes / 64) * 64;

        size_t tail = alignedBytes;
        size_t tmp;
        asm volatile(
            "2:\t\n"
            "cmpq %q[tail], %q[bytes]\t\n"
            "je 1f\t\n"
            "addq $-8, %q[bytes]\t\n"
            "movq (%q[src], %q[bytes], 1), %q[tmp]\t\n"
            "movq %q[tmp], (%q[dst], %q[bytes], 1)\t\n"
            "jmp 2b\t\n"

            "1:\t\n"
            "test %q[alignedBytes], %q[alignedBytes]\t\n"
            "jz 3f\t\n"

            ".balign 32\t\n"
            "100:\t\n"

            "movups -64(%q[src], %q[alignedBytes], 1), %%xmm0\t\n"
            "movups -48(%q[src], %q[alignedBytes], 1), %%xmm1\t\n"
            "movups -32(%q[src], %q[alignedBytes], 1), %%xmm2\t\n"
            "movups -16(%q[src], %q[alignedBytes], 1), %%xmm3\t\n"
            "movups %%xmm0, -64(%q[dst], %q[alignedBytes], 1)\t\n"
            "movups %%xmm1, -48(%q[dst], %q[alignedBytes], 1)\t\n"
            "movups %%xmm2, -32(%q[dst], %q[alignedBytes], 1)\t\n"
            "movups %%xmm3, -16(%q[dst], %q[alignedBytes], 1)\t\n"
            "addq $-64, %q[alignedBytes]\t\n"
            "jnz 100b\t\n"

            "3:\t\n"

            : [alignedBytes] "+r" (alignedBytes), [tail] "+r" (tail), [bytes] "+r" (bytes), [tmp] "+r" (tmp), [dst] "+r" (dst), [src] "+r" (src)
            :
            : "xmm0", "xmm1", "xmm2", "xmm3", "memory", "cc"
        );
#elif CPU(ARM64)
        uint64_t alignedBytes = (static_cast<uint64_t>(bytes) / 16) * 16;
        uint64_t dstPtr = static_cast<uint64_t>(bitwise_cast<uintptr_t>(dst));
        uint64_t srcPtr = static_cast<uint64_t>(bitwise_cast<uintptr_t>(src));

        asm volatile(
            "1:\t\n"
            "cmp %x[alignedBytes], %x[bytes]\t\n"
            "b.eq 2f\t\n"
            "sub %x[bytes], %x[bytes], #0x8\t\n"
            "ldr d0, [%x[srcPtr], %x[bytes]]\t\n"
            "str d0, [%x[dstPtr], %x[bytes]]\t\n"
            "b 1b\t\n"

            "2:\t\n"
            "cbz %x[alignedBytes], 3f\t\n"
            "sub %x[alignedBytes], %x[alignedBytes], #0x10\t\n"
            "ldr q0, [%x[srcPtr], %x[alignedBytes]]\t\n"
            "str q0, [%x[dstPtr], %x[alignedBytes]]\t\n"
            "b 2b\t\n"

            "3:\t\n"

            : [alignedBytes] "+r" (alignedBytes), [bytes] "+r" (bytes), [dstPtr] "+r" (dstPtr), [srcPtr] "+r" (srcPtr)
            :
            : "d0", "d1", "memory"
        );
#endif // CPU(X86_64)
    }
#else
    slowPathBackwardsMemmove();
#endif // COMPILER(GCC_COMPATIBLE) && (CPU(X86_64) || CPU(ARM64))
#else
    memmove(dst, src, bytes);
#endif // USE(JSVALUE64)
}

template <typename T>
ALWAYS_INLINE void gcSafeZeroMemory(T* dst, size_t bytes)
{
    static_assert(sizeof(T) == sizeof(JSValue));
    RELEASE_ASSERT(bytes % 8 == 0);
#if USE(JSVALUE64)
#if COMPILER(GCC_COMPATIBLE) && (CPU(X86_64) || CPU(ARM64))
#if CPU(X86_64)
    uint64_t zero = 0;
    size_t count = bytes / 8;
    asm volatile (
        "rep stosq\n\t"
        : "+D"(dst), "+c"(count)
        : "a"(zero)
        : "memory"
    );
#elif CPU(ARM64)
    uint64_t alignedBytes = (static_cast<uint64_t>(bytes) / 64) * 64;
    uint64_t dstPtr = static_cast<uint64_t>(bitwise_cast<uintptr_t>(dst));
    uint64_t end = dstPtr + bytes;
    uint64_t alignedEnd = dstPtr + alignedBytes;
    asm volatile(
        "movi d0, #0\t\n"
        "movi d1, #0\t\n"

        ".p2align 4\t\n"
        "2:\t\n"
        "cmp %x[dstPtr], %x[alignedEnd]\t\n"
        "b.eq 4f\t\n"
        "stnp q0, q0, [%x[dstPtr]]\t\n"
        "stnp q0, q0, [%x[dstPtr], #0x20]\t\n"
        "add %x[dstPtr], %x[dstPtr], #0x40\t\n"
        "b 2b\t\n"

        "4:\t\n"
        "cmp %x[dstPtr], %x[end]\t\n"
        "b.eq 5f\t\n"
        "str d0, [%x[dstPtr]], #0x8\t\n"
        "b 4b\t\n"

        "5:\t\n"

        : [alignedBytes] "+r" (alignedBytes), [bytes] "+r" (bytes), [dstPtr] "+r" (dstPtr), [end] "+r" (end), [alignedEnd] "+r" (alignedEnd)
        :
        : "d0", "d1", "memory"
    );
#endif // CPU(X86_64)
#else
    size_t count = bytes / 8;
    for (size_t i = 0; i < count; ++i)
        bitwise_cast<volatile uint64_t*>(dst)[i] = 0;
#endif // COMPILER(GCC_COMPATIBLE) && (CPU(X86_64) || CPU(ARM64))
#else
    memset(reinterpret_cast<char*>(dst), 0, bytes);
#endif // USE(JSVALUE64)
}

} // namespace JSC