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 #include "berberis/lite_translator/lite_translate_region.h"
17
18 #include <cstdint>
19 #include <limits>
20 #include <tuple>
21
22 #include "berberis/assembler/machine_code.h"
23 #include "berberis/base/checks.h"
24 #include "berberis/code_gen_lib/code_gen_lib.h"
25 #include "berberis/decoder/riscv64/decoder.h"
26 #include "berberis/decoder/riscv64/semantics_player.h"
27 #include "berberis/guest_state/guest_addr.h"
28
29 #include "riscv64_to_x86_64/lite_translator.h"
30
31 namespace berberis {
32
33 namespace {
34
Finalize(LiteTranslator * translator,GuestAddr pc)35 void Finalize(LiteTranslator* translator, GuestAddr pc) {
36 translator->ExitRegion(pc);
37 translator->as()->Finalize();
38 }
39
GenIncrementProfileCounter(x86_64::Assembler * as,const LiteTranslateParams & params)40 void GenIncrementProfileCounter(x86_64::Assembler* as, const LiteTranslateParams& params) {
41 CHECK(params.counter_location);
42 *params.counter_location = 0;
43
44 // Ideally for thread safety the counter subtraction needs to be atomic. But,
45 // our experiments showed that the overhead from LOCK prefix here is too high
46 // (b/222363018#comment3).
47 // The threshold for the counter is an heuristic though. The worst what can
48 // happen due to racing threads is counter inadvertently rolling back to a
49 // value a few increments before, which we consider acceptable.
50 // WARNING: do not clobber rax, since insn_addr held in it is used in case of
51 // the reached threshold.
52 as->Movq(as->rcx, bit_cast<int64_t>(params.counter_location));
53 static_assert(sizeof(*params.counter_location) == 4);
54 as->Addl({.base = as->rcx}, 1);
55 as->Cmpl({.base = as->rcx}, params.counter_threshold);
56 as->Jcc(x86_64::Assembler::Condition::kGreater, params.counter_threshold_callback);
57 }
58
59 // Returns the success status and
60 // - in case of success, the pc of the next instruction past the translated region
61 // - in case of failure, the pc of the failed instruction
62 // Specifically, returnes input pc if we cannot translate even the first instruction.
TryLiteTranslateRegionImpl(GuestAddr start_pc,GuestAddr end_pc,MachineCode * machine_code,LiteTranslateParams params)63 std::tuple<bool, GuestAddr> TryLiteTranslateRegionImpl(GuestAddr start_pc,
64 GuestAddr end_pc,
65 MachineCode* machine_code,
66 LiteTranslateParams params) {
67 CHECK_LT(start_pc, end_pc);
68 LiteTranslator translator(machine_code, start_pc, params);
69 SemanticsPlayer sem_player(&translator);
70 Decoder decoder(&sem_player);
71
72 if (params.enable_self_profiling) {
73 GenIncrementProfileCounter(translator.as(), params);
74 }
75
76 while (translator.GetInsnAddr() != end_pc && !translator.is_region_end_reached()) {
77 uint8_t insn_size = decoder.Decode(ToHostAddr<const uint16_t>(translator.GetInsnAddr()));
78 if (!translator.success()) {
79 return {false, translator.GetInsnAddr()};
80 }
81 translator.FreeTempRegs();
82 translator.IncrementInsnAddr(insn_size);
83 }
84
85 Finalize(&translator, translator.GetInsnAddr());
86
87 return {translator.success(), translator.GetInsnAddr()};
88 }
89
90 } // namespace
91
LiteTranslateRange(GuestAddr start_pc,GuestAddr end_pc,MachineCode * machine_code,LiteTranslateParams params)92 bool LiteTranslateRange(GuestAddr start_pc,
93 GuestAddr end_pc,
94 MachineCode* machine_code,
95 LiteTranslateParams params) {
96 auto [success, stop_pc] = TryLiteTranslateRegionImpl(start_pc, end_pc, machine_code, params);
97 return success;
98 }
99
TryLiteTranslateRegion(GuestAddr start_pc,MachineCode * machine_code,LiteTranslateParams params)100 std::tuple<bool, GuestAddr> TryLiteTranslateRegion(GuestAddr start_pc,
101 MachineCode* machine_code,
102 LiteTranslateParams params) {
103 // This effectively makes translating code at max guest address impossible, but we
104 // assume that it's not practically significant.
105 return TryLiteTranslateRegionImpl(
106 start_pc, std::numeric_limits<GuestAddr>::max(), machine_code, params);
107 }
108
109 } // namespace berberis
110