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Arm64: Removes a vtable indirection in syscalls #3327

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Jan 5, 2024
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Arm64: Removes a vtable indirection in syscalls #3327

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f990214
Utils: Add ability to get VTable entries to PMF helper
Sonicadvance1 Dec 12, 2023
266f7fe
Arm64: Removes a vtable indirection in syscalls
Sonicadvance1 Dec 12, 2023
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32 changes: 30 additions & 2 deletions FEXCore/Source/Utils/MemberFunctionToPointer.h
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Original file line number Diff line number Diff line change
Expand Up @@ -17,24 +17,52 @@ class MemberFunctionToPointerCast final {
public:
MemberFunctionToPointerCast(PointerToMemberType Function) {
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This seems to lose the assertions. Is that intended?

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Intended, the asserts get moved to the accessor functions GetConvertedPointer and GetVTableOffset instead.

memcpy(&PMF, &Function, sizeof(PMF));
}

uintptr_t GetConvertedPointer() const {
#ifdef _M_X86_64
// Itanium C++ ABI (https://itanium-cxx-abi.github.io/cxx-abi/abi.html#member-function-pointers)
// Low bit of ptr specifies if this Member function pointer is virtual or not
// Throw an assert if we were trying to cast a virtual member
LOGMAN_THROW_AA_FMT((PMF.ptr & 1) == 0, "C++ Pointer-To-Member representation didn't have low bit set to 0. Are you trying to cast a virtual member?");
#elif defined(_M_ARM_64 )
#elif defined(_M_ARM_64)
// C++ ABI for the Arm 64-bit Architecture (IHI 0059E)
// 4.2.1 Representation of pointer to member function
// Differs from Itanium specification
LOGMAN_THROW_AA_FMT(PMF.adj == 0, "C++ Pointer-To-Member representation didn't have adj == 0. Are you trying to cast a virtual member?");
#else
#error Don't know how to cast Member to function here. Likely just Itanium
#endif
return PMF.ptr;
}

uintptr_t GetConvertedPointer() const {
// Gets the vtable entry position of a virtual member function.
size_t GetVTableOffset() const {
#ifdef _M_X86_64
// Itanium C++ ABI (https://itanium-cxx-abi.github.io/cxx-abi/abi.html#member-function-pointers)
// Low bit of ptr specifies if this Member function pointer is virtual or not
// Throw an assert if we are not loading a virtual member.
LOGMAN_THROW_AA_FMT((PMF.ptr & 1) == 1, "C++ Pointer-To-Member representation didn't have low bit set to 1. This cast only works for virtual members.");
return PMF.ptr & ~1ULL;
#elif defined(_M_ARM_64)
// C++ ABI for the Arm 64-bit Architecture (IHI 0059E)
// 4.2.1 Representation of pointer to member function
// Differs from Itanium specification
LOGMAN_THROW_AA_FMT((PMF.adj & 1) == 1, "C++ Pointer-To-Member representation didn't have adj == 1. This cast only works for virtual members.");
return PMF.ptr;
#else
#error Don't know how to cast Member to function here. Likely just Itanium
#endif
}

// Gets the pointer to the vtable entry for the object passed it.
template<typename Class>
uintptr_t GetVTableEntry(Class *VirtualClass) const {
// VTable is always stored at the beginning of a class object.
uintptr_t *VTable = *reinterpret_cast<uintptr_t**>(VirtualClass);

size_t Offset = GetVTableOffset() / sizeof(void*);
return VTable[Offset];
}

private:
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