/*
 * Copyright (C) 2023 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "berberis/runtime_primitives/runtime_library.h"

#include <cstdint>
#include <cstring>

#include "berberis/calling_conventions/calling_conventions_riscv64.h"
#include "berberis/guest_abi/guest_arguments.h"
#include "berberis/guest_os_primitives/guest_thread_manager.h"
#include "berberis/guest_os_primitives/scoped_pending_signals.h"
#include "berberis/guest_state/guest_addr.h"
#include "berberis/guest_state/guest_state_arch.h"
#include "berberis/instrument/guest_call.h"
#include "berberis/runtime_primitives/virtual_guest_call_frame.h"

namespace berberis {

// Call a guest function from the host with the given arguments. The return
// value is stored in the first argument of the buffer after the call returns.
//
// Within the guest call stack, the host has its own call frame. This stack
// frame is allocated by the ScopedVirtualGuestCallFrame instance. Virtual guest call frame
// simulates the minimum necessary prologue and epilogue for saving and
// restoring the frame pointer and return address on the stack. Within that call
// frame, we can make further adjustments to the stack pointer, such as
// allocating space on the stack for arguments that spill past the registers.
//
// To visualize this, consider a guest function GuestFuncA, which calls
// HostFuncB, with no arguments:
//   void GuestFuncA() {
//     HostFuncB();
//   }
//
// HostFuncB then calls GuestFuncC with 100 arguments:
//   void HostFuncB() {
//     GuestFuncC(1, 2, 3, ..., 98, 99, 100);
//   }
//
// At the time that HostFuncB calls GuestFuncC, GuestFuncA is at the top of the
// guest call stack because HostFuncB was entered directly. If no call frame for
// the host function is created, GuestFuncA would call GuestFuncC directly from
// the perspective of the guest. The arguments for GuestFuncC would appear in
// GuestFuncA's frame.
//
// RISC-V uses a calling convention with caller clean-up. In these types of
// calling conventions, the caller is responsible for deallocating arguments
// passed on the stack after the callee returns. However, GuestFuncC is unaware
// of these arguments, so a stand-in call frame for HostFuncB, GuestFuncCCaller,
// is created. GuestFuncCCaller populates the stack arguments for GuestFuncC,
// makes the call, and then deallocates the frame.
void RunGuestCall(GuestAddr pc, GuestArgumentBuffer* buf) {
  GuestThread* thread = GetCurrentGuestThread();
  ThreadState* state = thread->state();

  ScopedPendingSignalsEnabler scoped_pending_signals_enabler(thread);

  ScopedVirtualGuestCallFrame virtual_guest_call_frame(&state->cpu, pc);

  // Copy argc int and fp_argc float registers for the arguments into the argument buffer.
  memcpy(&(state->cpu.x[A0]), buf->argv, buf->argc * sizeof(buf->argv[0]));
  memcpy(&(state->cpu.f[FA0]), buf->fp_argv, buf->fp_argc * sizeof(buf->fp_argv[0]));

  // sp -= stack_argc
  SetXReg<SP>(state->cpu, GetXReg<SP>(state->cpu) - buf->stack_argc);
  // sp = align_down(sp, ...)
  SetXReg<SP>(
      state->cpu,
      AlignDown(GetXReg<SP>(state->cpu), riscv64::CallingConventions::kStackAlignmentBeforeCall));

  memcpy(ToHostAddr<void>(GetXReg<SP>(state->cpu)), buf->stack_argv, buf->stack_argc);

  if (kInstrumentWrappers) {
    OnWrappedGuestCall(state, pc);
  }

  ExecuteGuestCall(state);

  if (kInstrumentWrappers) {
    OnWrappedGuestReturn(state, pc);
  }

  // Copy resc int and fp_resc float registers for the results from the buffer to the cpu state.
  memcpy(buf->argv, &(state->cpu.x[A0]), buf->resc * sizeof(buf->argv[0]));
  memcpy(buf->fp_argv, &(state->cpu.f[FA0]), buf->fp_resc * sizeof(buf->fp_argv[0]));
}

}  // namespace berberis