Source/JavaScriptCore/wasm/WasmBinding.cpp

/*
 * Copyright (C) 2016-2019 Apple Inc. All rights reserved.
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#include "config.h"
#include "WasmBinding.h"

#if ENABLE(WEBASSEMBLY)

#include "CCallHelpers.h"
#include "JSCInlines.h"
#include "LinkBuffer.h"
#include "WasmCallingConvention.h"
#include "WasmInstance.h"

namespace JSC { namespace Wasm {

using JIT = CCallHelpers;

Expected<MacroAssemblerCodeRef<WasmEntryPtrTag>, BindingFailure> wasmToWasm(unsigned importIndex)
{
    // FIXME: Consider uniquify the stubs based on signature + index to see if this saves memory.
    // https://bugs.webkit.org/show_bug.cgi?id=184157

    const PinnedRegisterInfo& pinnedRegs = PinnedRegisterInfo::get();
    JIT jit;

    GPRReg scratch = wasmCallingConventionAir().prologueScratch(0);
    GPRReg baseMemory = pinnedRegs.baseMemoryPointer;
    ASSERT(baseMemory != scratch);
    ASSERT(pinnedRegs.sizeRegister != baseMemory);
    ASSERT(pinnedRegs.sizeRegister != scratch);
    GPRReg sizeRegAsScratch = pinnedRegs.sizeRegister;

    // B3's call codegen ensures that the JSCell is a WebAssemblyFunction.
    jit.loadWasmContextInstance(sizeRegAsScratch); // Old Instance*
    // Get the callee's Wasm::Instance and set it as WasmContext's instance. The caller will take care of restoring its own Instance.
    jit.loadPtr(JIT::Address(sizeRegAsScratch, Instance::offsetOfTargetInstance(importIndex)), baseMemory); // Instance*.
    // While we're accessing that cacheline, also get the wasm entrypoint so we can tail call to it below.
    jit.loadPtr(JIT::Address(sizeRegAsScratch, Instance::offsetOfWasmEntrypointLoadLocation(importIndex)), scratch);
    jit.storeWasmContextInstance(baseMemory);

    jit.loadPtr(JIT::Address(sizeRegAsScratch, Instance::offsetOfCachedStackLimit()), sizeRegAsScratch);
    jit.storePtr(sizeRegAsScratch, JIT::Address(baseMemory, Instance::offsetOfCachedStackLimit()));

    // FIXME the following code assumes that all Wasm::Instance have the same pinned registers. https://bugs.webkit.org/show_bug.cgi?id=162952
    // Set up the callee's baseMemory register as well as the memory size registers.
    {
        GPRReg scratchOrSize = !Gigacage::isEnabled(Gigacage::Primitive) ? pinnedRegs.sizeRegister : wasmCallingConventionAir().prologueScratch(1);

        jit.loadPtr(JIT::Address(baseMemory, Wasm::Instance::offsetOfCachedMemorySize()), pinnedRegs.sizeRegister); // Memory size.
        jit.loadPtr(JIT::Address(baseMemory, Wasm::Instance::offsetOfCachedMemory()), baseMemory); // Wasm::Memory::TaggedArrayStoragePtr<void> (void*).
        jit.cageConditionally(Gigacage::Primitive, baseMemory, pinnedRegs.sizeRegister, scratchOrSize);
    }

    // Tail call into the callee WebAssembly function.
    jit.loadPtr(scratch, scratch);
    jit.jump(scratch, WasmEntryPtrTag);

    LinkBuffer patchBuffer(jit, GLOBAL_THUNK_ID, JITCompilationCanFail);
    if (UNLIKELY(patchBuffer.didFailToAllocate()))
        return makeUnexpected(BindingFailure::OutOfMemory);

    return FINALIZE_CODE(patchBuffer, WasmEntryPtrTag, "WebAssembly->WebAssembly import[%i]", importIndex);
}

} } // namespace JSC::Wasm

#endif // ENABLE(WEBASSEMBLY)