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// license:BSD-3-Clause
// copyright-holders:Vas Crabb
/***************************************************************************
mfpresolve.h
Helpers for resolving member function pointers to entry points.
***************************************************************************/
#include "mfpresolve.h"
#include "osdcomm.h"
#include <cstdio>
//**************************************************************************
// MACROS
//**************************************************************************
#if defined(MAME_DELEGATE_LOG_ADJ)
#define LOG(...) printf(__VA_ARGS__)
#else
#define LOG(...) do { if (false) printf(__VA_ARGS__); } while (false)
#endif
namespace util::detail {
std::pair<std::uintptr_t, std::uintptr_t> resolve_member_function_itanium(
std::uintptr_t function,
std::ptrdiff_t delta,
void const *object) noexcept
{
// apply the "this" delta to the object first - the value is shifted to the left one bit position for the ARM-like variant
LOG("Input this=%p ptr=%p adj=%ld ", object, reinterpret_cast<void const *>(function), long(delta));
constexpr int deltashift = (MAME_ABI_CXX_ITANIUM_MFP_TYPE == MAME_ABI_CXX_ITANIUM_MFP_ARM) ? 1 : 0;
object = reinterpret_cast<std::uint8_t const *>(object) + (delta >> deltashift);
LOG("Calculated this=%p ", object);
// test the virtual member function flag - it's the low bit of either the ptr or adj field, depending on the variant
if ((MAME_ABI_CXX_ITANIUM_MFP_TYPE == MAME_ABI_CXX_ITANIUM_MFP_ARM) ? !(delta & 1) : !(function & 1))
{
// conventional function pointer
LOG("ptr=%p\n", reinterpret_cast<void const *>(function));
return std::make_pair(function, std::uintptr_t(object));
}
else
{
// byte index into the vtable to the function
auto const vtable_ptr = *reinterpret_cast<std::uint8_t const *const *>(object) + function - ((MAME_ABI_CXX_ITANIUM_MFP_TYPE == MAME_ABI_CXX_ITANIUM_MFP_ARM) ? 0 : 1);
std::uintptr_t result;
if (MAME_ABI_CXX_VTABLE_FNDESC)
result = std::uintptr_t(vtable_ptr);
else
result = *reinterpret_cast<std::uintptr_t const *>(vtable_ptr);
LOG("ptr=%p (vtable)\n", reinterpret_cast<void const *>(result));
return std::make_pair(result, std::uintptr_t(object));
}
}
std::pair<std::uintptr_t, std::uintptr_t> resolve_member_function_msvc(
void const *funcptr,
std::size_t size,
void const *object) noexcept
{
struct single { std::uintptr_t entrypoint; };
struct multi { std::uintptr_t entrypoint; int this_delta; };
struct { std::uintptr_t entrypoint; int this_delta; int vptr_offs; int vt_index; } const *unknown;
assert(sizeof(*unknown) >= size);
unknown = reinterpret_cast<decltype(unknown)>(funcptr);
LOG("Input this=%p ", object);
if (sizeof(single) < size)
LOG("thisdelta=%d ", unknown->this_delta);
if (sizeof(*unknown) == size)
LOG("vptrdelta=%d vindex=%d ", unknown->vptr_offs, unknown->vt_index);
auto byteptr = reinterpret_cast<std::uint8_t const *>(object);
// test for pointer to member function cast across virtual inheritance relationship
if ((sizeof(*unknown) == size) && unknown->vt_index)
{
// add offset from "this" pointer to location of vptr, and add offset to virtual base from vtable
byteptr += unknown->vptr_offs;
std::uint8_t const *const vptr = *reinterpret_cast<std::uint8_t const *const *>(byteptr);
byteptr += *reinterpret_cast<int const *>(vptr + unknown->vt_index);
}
// add "this" pointer displacement if present in the pointer to member function
if (sizeof(single) < size)
byteptr += unknown->this_delta;
LOG("Calculated this=%p\n", reinterpret_cast<void const *>(byteptr));
// walk past recognisable thunks
return std::make_pair(bypass_member_function_thunks(unknown->entrypoint, byteptr), std::uintptr_t(byteptr));
}
std::uintptr_t bypass_member_function_thunks(
std::uintptr_t entrypoint,
void const *object) noexcept
{
#if defined(__x86_64__) || defined(_M_X64)
std::uint8_t const *func = reinterpret_cast<std::uint8_t const *>(entrypoint);
while (true)
{
// Assumes Windows calling convention, and doesn't consider that
// the "this" pointer could be in RDX if RCX is a pointer to
// space for an oversize scalar result. Since the result area
// is uninitialised on entry, you won't see something that looks
// like a vtable dispatch through RCX in this case - it won't
// behave badly, it just won't bypass virtual call thunks in the
// rare situations where the return type is an oversize scalar.
if (0xe9 == func[0])
{
// relative jump with 32-bit displacement (typically a resolved PLT entry)
LOG("Found relative jump at %p ", func);
func += std::ptrdiff_t(5) + *reinterpret_cast<std::int32_t const *>(func + 1);
LOG("redirecting to %p\n", func);
continue;
}
else if (object && (0x48 == func[0]) && (0x8b == func[1]) && (0x01 == func[2]))
{
if ((0xff == func[3]) && ((0x20 == func[4]) || (0x60 == func[4]) || (0xa0 == func[4])))
{
// MSVC virtual function call thunk - mov rax,QWORD PTR [rcx] ; jmp QWORD PTR [rax+...]
LOG("Found virtual member function thunk at %p ", func);
std::uint8_t const *const vptr = *reinterpret_cast<std::uint8_t const *const *>(object);
if (0x20 == func[4]) // no displacement
func = *reinterpret_cast<std::uint8_t const *const *>(vptr);
else if (0x60 == func[4]) // 8-bit displacement
func = *reinterpret_cast<std::uint8_t const *const *>(vptr + *reinterpret_cast<std::int8_t const *>(func + 5));
else // 32-bit displacement
func = *reinterpret_cast<std::uint8_t const *const *>(vptr + *reinterpret_cast<std::int32_t const *>(func + 5));
LOG("redirecting to %p\n", func);
continue;
}
else if ((0x48 == func[3]) && (0x8b == func[4]))
{
// clang virtual function call thunk - mov rax,QWORD PTR [rcx] ; mov rax,QWORD PTR [rax+...] ; jmp rax
if ((0x00 == func[5]) && (0x48 == func[6]) && (0xff == func[7]) && (0xe0 == func[8]))
{
// no displacement
LOG("Found virtual member function thunk at %p ", func);
std::uint8_t const *const vptr = *reinterpret_cast<std::uint8_t const *const *>(object);
func = *reinterpret_cast<std::uint8_t const *const *>(vptr);
LOG("redirecting to %p\n", func);
continue;
}
else if ((0x40 == func[5]) && (0x48 == func[7]) && (0xff == func[8]) && (0xe0 == func[9]))
{
// 8-bit displacement
LOG("Found virtual member function thunk at %p ", func);
std::uint8_t const *const vptr = *reinterpret_cast<std::uint8_t const *const *>(object);
func = *reinterpret_cast<std::uint8_t const *const *>(vptr + *reinterpret_cast<std::int8_t const *>(func + 6));
LOG("redirecting to %p\n", func);
continue;
}
else if ((0x80 == func[5]) && (0x48 == func[10]) && (0xff == func[11]) && (0xe0 == func[12]))
{
// 32-bit displacement
LOG("Found virtual member function thunk at %p ", func);
std::uint8_t const *const vptr = *reinterpret_cast<std::uint8_t const *const *>(object);
func = *reinterpret_cast<std::uint8_t const *const *>(vptr + *reinterpret_cast<std::int32_t const *>(func + 6));
LOG("redirecting to %p\n", func);
continue;
}
}
}
// clang uses unoptimised thunks if optimisation is disabled
// Without optimisation, clang produces thunks like:
// 50 push rax
// 48 89 0c 24 mov QWORD PTR [rsp],rcx
// 48 8b 0c 24 mov rcx,QWORD PTR [rsp]
// 48 8b 01 mov rax,QWORD PTR [rcx]
// 48 8b 80 xx xx xx xx mov rax,QWORD PTR [rax+...]
// 41 5a pop r10
// 48 ff e0 jmp rax
// Trying to decode these thunks likely isn't worth the effort.
// Chasing performance in unoptimised builds isn't very useful,
// and the format of these thunks may be fragile.
// not something we can easily bypass
break;
}
return std::uintptr_t(func);
#elif defined(__aarch64__) || defined(_M_ARM64)
std::uint32_t const *func = reinterpret_cast<std::uint32_t const *>(entrypoint);
auto const fetch = [&func] (auto offset) { return little_endianize_int32(func[offset]); };
while (true)
{
if ((0x90000010 == (fetch(0) & 0x9f00001f)) && (0x91000210 == (fetch(1) & 0xffc003ff)) && (0xd61f0200 == fetch(2)))
{
// page-relative jump with +/-4GB reach - adrp xip0,... ; add xip0,xip0,#... ; br xip0
LOG("Found page-relative jump at %p ", func);
std::int64_t const page =
(std::uint64_t(fetch(0) & 0x60000000) >> 17) |
(std::uint64_t(fetch(0) & 0x00ffffe0) << 9) |
((fetch(0) & 0x00800000) ? (~std::uint64_t(0) << 33) : 0);
std::uint32_t const offset = (fetch(1) & 0x003ffc00) >> 10;
func = reinterpret_cast<std::uint32_t const *>(((std::uintptr_t(func) + page) & (~std::uintptr_t(0) << 12)) + offset);
LOG("redirecting to %p\n", func);
}
else if (object && (0xf9400010 == fetch(0)) && (0xf9400210 == (fetch(1) & 0xffc003ff)) && (0xd61f0200 == fetch(2)))
{
// virtual function call thunk - ldr xip0,[x0] ; ldr xip0,[x0,#...] ; br xip0
LOG("Found virtual member function thunk at %p ", func);
auto const vptr = *reinterpret_cast<std::uint32_t const *const *const *>(object);
func = vptr[(fetch(1) & 0x003ffc00) >> 10];
LOG("redirecting to %p\n", func);
}
else
{
// not something we can easily bypass
break;
}
// clang uses horribly sub-optimal thunks for AArch64
// Without optimisation, clang produces thunks like:
// d10143ff sub sp,sp,#80
// f90027e7 str x7,[sp,#72]
// f90023e6 str x6,[sp,#64]
// f9001fe5 str x5,[sp,#56]
// f9001be4 str x4,[sp,#48]
// f90017e3 str x3,[sp,#40]
// f90013e2 str x2,[sp,#32]
// f9000fe1 str x1,[sp,#24]
// f90007e0 str x0,[sp,#8]
// f94007e0 ldr x0,[sp,#8]
// f9400009 ldr x9,[x0]
// f9400129 ldr x9,[x9,#...]
// 910143ff add sp,sp,#80
// d61f0120 br x9
// With optimisation, clang produces thunks like:
// d10103ff sub sp,sp,#64
// a9008be1 stp x1,x2,[sp,#8]
// a90193e3 stp x3,x4,[sp,#24]
// a9029be5 stp x5,x6,[sp,#40]
// f9001fe7 str x7,[sp,#56]
// f9400009 ldr x9,[x0]
// f9400129 ldr x9,[x9,#...]
// 910103ff add sp,sp,#64
// d61f0120 br x9
// It's more effort than it's worth to try decoding these
// thunks.
}
return std::uintptr_t(func);
#else
return entrypoint;
#endif
}
} // namespace util::detail
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