1 /* 2 * Copyright (C) 2023 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #ifndef BERBERIS_RUNTIME_PRIMITIVES_VIRTUAL_GUEST_CALL_FRAME_H_ 18 #define BERBERIS_RUNTIME_PRIMITIVES_VIRTUAL_GUEST_CALL_FRAME_H_ 19 20 #include "berberis/guest_state/guest_addr.h" 21 #include "berberis/guest_state/guest_state_opaque.h" 22 23 namespace berberis { 24 25 // Set state for calling guest function at given pc (except arguments passing). 26 // Restore previous state after guest function returns. 27 // 28 // Assume we have some meaningful guest state, for example, at trampoline or at signal handler call. 29 // We want to call nested guest function, for example, callback passed into trampoline or guest 30 // signal handler. We want to restore the state after guest nested function returns. 31 // 32 // Assume guest function to be called conforms to procedure calling standard. In particular, it is 33 // expected to preserve caller-saved registers, and to return by jumping to a given return address. 34 // 35 // Assume we want to allow guest unwinder to unwind to the previous guest state. For that, we should 36 // only save state into guest accessible memory - namely, into guest stack/registers. 37 // 38 // First, we want guest execution to stop when guest function returns. For that, we provide special 39 // return address that is treated as stop by dispatcher. 40 // 41 // Next, parameters are passed afterwards, so at this point we don't know how much stack they will 42 // need. To restore stack after the call, we need to save current stack pointer in a caller-saved 43 // register. 44 // 45 // Finally, we need to save the registers that are not preserved by guest function. 46 class ScopedVirtualGuestCallFrame { 47 public: 48 ScopedVirtualGuestCallFrame(CPUState* cpu, GuestAddr pc); 49 ~ScopedVirtualGuestCallFrame(); 50 SetReturnAddress(GuestAddr ra)51 static void SetReturnAddress(GuestAddr ra) { g_return_address_ = ra; } 52 53 private: 54 static GuestAddr g_return_address_; 55 56 CPUState* cpu_; 57 58 // For safety checks! 59 GuestAddr stack_pointer_; 60 GuestAddr link_register_; 61 GuestAddr program_counter_; 62 }; 63 64 // Set return address for guest calls. On this address, guest execution will stop. 65 void InitVirtualGuestCallFrameReturnAddress(GuestAddr ra); 66 67 } // namespace berberis 68 69 #endif // BERBERIS_RUNTIME_PRIMITIVES_VIRTUAL_GUEST_CALL_FRAME_H_ 70