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 * Copyright (C) 2016-2021 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.
 *
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 * 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
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 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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#include "config.h"
#include "WasmBinding.h"

#if ENABLE(WEBASSEMBLY)

#include "CCallHelpers.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 = wasmCallingConvention().prologueScratchGPRs[0];
    GPRReg baseMemory = pinnedRegs.baseMemoryPointer;
    ASSERT(baseMemory != GPRReg::InvalidGPRReg);
    ASSERT(baseMemory != scratch);
    ASSERT(pinnedRegs.boundsCheckingSizeRegister != baseMemory);
    ASSERT(pinnedRegs.boundsCheckingSizeRegister != scratch);
    GPRReg sizeRegAsScratch = pinnedRegs.boundsCheckingSizeRegister;
    ASSERT(sizeRegAsScratch != GPRReg::InvalidGPRReg);

    // 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.
    {
        jit.loadPtr(JIT::Address(baseMemory, Wasm::Instance::offsetOfCachedBoundsCheckingSize()), pinnedRegs.boundsCheckingSizeRegister); // Bound checking size.
        jit.loadPtr(JIT::Address(baseMemory, Wasm::Instance::offsetOfCachedMemory()), baseMemory); // Wasm::Memory::TaggedArrayStoragePtr<void> (void*).
        jit.cageConditionallyAndUntag(Gigacage::Primitive, baseMemory, pinnedRegs.boundsCheckingSizeRegister, wasmCallingConvention().prologueScratchGPRs[1]);
    }

    // Tail call into the callee WebAssembly function.
    jit.loadPtr(JIT::Address(scratch), scratch);
    jit.farJump(scratch, WasmEntryPtrTag);

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

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

} } // namespace JSC::Wasm

#endif // ENABLE(WEBASSEMBLY)