1//===-- WatchpointAlgorithms.cpp ------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#include "lldb/Breakpoint/WatchpointAlgorithms.h"
10#include "lldb/Breakpoint/WatchpointResource.h"
11#include "lldb/Target/Process.h"
12#include "lldb/Utility/ArchSpec.h"
13#include "lldb/Utility/LLDBLog.h"
14#include "lldb/Utility/Log.h"
15
16#include <algorithm>
17#include <utility>
18#include <vector>
19
20using namespace lldb;
21using namespace lldb_private;
22
23std::vector<WatchpointResourceSP>
24WatchpointAlgorithms::AtomizeWatchpointRequest(
25 addr_t addr, size_t size, bool read, bool write,
26 WatchpointHardwareFeature supported_features, ArchSpec &arch) {
27
28 std::vector<Region> entries;
29
30 if (supported_features & eWatchpointHardwareArmMASK) {
31 entries =
32 PowerOf2Watchpoints(user_addr: addr, user_size: size,
33 /*min_byte_size*/ 1,
34 /*max_byte_size*/ INT32_MAX,
35 /*address_byte_size*/ arch.GetAddressByteSize());
36 } else {
37 // As a fallback, assume we can watch any power-of-2
38 // number of bytes up through the size of an address in the target.
39 entries =
40 PowerOf2Watchpoints(user_addr: addr, user_size: size,
41 /*min_byte_size*/ 1,
42 /*max_byte_size*/ arch.GetAddressByteSize(),
43 /*address_byte_size*/ arch.GetAddressByteSize());
44 }
45
46 Log *log = GetLog(mask: LLDBLog::Watchpoints);
47 LLDB_LOGV(log, "AtomizeWatchpointRequest user request addr {0:x} size {1}",
48 addr, size);
49 std::vector<WatchpointResourceSP> resources;
50 for (Region &ent : entries) {
51 LLDB_LOGV(log, "AtomizeWatchpointRequest creating resource {0:x} size {1}",
52 ent.addr, ent.size);
53 WatchpointResourceSP wp_res_sp =
54 std::make_shared<WatchpointResource>(args&: ent.addr, args&: ent.size, args&: read, args&: write);
55 resources.push_back(x: wp_res_sp);
56 }
57
58 return resources;
59}
60
61/// Convert a user's watchpoint request (\a user_addr and \a user_size)
62/// into hardware watchpoints, for a target that can watch a power-of-2
63/// region of memory (1, 2, 4, 8, etc), aligned to that same power-of-2
64/// memory address.
65///
66/// If a user asks to watch 4 bytes at address 0x1002 (0x1002-0x1005
67/// inclusive) we can implement this with two 2-byte watchpoints
68/// (0x1002 and 0x1004) or with an 8-byte watchpoint at 0x1000.
69/// A 4-byte watchpoint at 0x1002 would not be properly 4 byte aligned.
70///
71/// If a user asks to watch 16 bytes at 0x1000, and this target supports
72/// 8-byte watchpoints, we can implement this with two 8-byte watchpoints
73/// at 0x1000 and 0x1008.
74std::vector<WatchpointAlgorithms::Region>
75WatchpointAlgorithms::PowerOf2Watchpoints(addr_t user_addr, size_t user_size,
76 size_t min_byte_size,
77 size_t max_byte_size,
78 uint32_t address_byte_size) {
79
80 Log *log = GetLog(mask: LLDBLog::Watchpoints);
81 LLDB_LOGV(log,
82 "AtomizeWatchpointRequest user request addr {0:x} size {1} "
83 "min_byte_size {2}, max_byte_size {3}, address_byte_size {4}",
84 user_addr, user_size, min_byte_size, max_byte_size,
85 address_byte_size);
86
87 // Can't watch zero bytes.
88 if (user_size == 0)
89 return {};
90
91 size_t aligned_size = std::max(a: user_size, b: min_byte_size);
92 /// Round up \a user_size to the next power-of-2 size
93 /// user_size == 8 -> aligned_size == 8
94 /// user_size == 9 -> aligned_size == 16
95 aligned_size = llvm::bit_ceil(Value: aligned_size);
96
97 addr_t aligned_start = user_addr & ~(aligned_size - 1);
98
99 // Does this power-of-2 memory range, aligned to power-of-2 that the
100 // hardware can watch, completely cover the requested region.
101 if (aligned_size <= max_byte_size &&
102 aligned_start + aligned_size >= user_addr + user_size)
103 return {{.addr: aligned_start, .size: aligned_size}};
104
105 // If the maximum region we can watch is larger than the aligned
106 // size, try increasing the region size by one power of 2 and see
107 // if aligning to that amount can cover the requested region.
108 //
109 // Increasing the aligned_size repeatedly instead of splitting the
110 // watchpoint can result in us watching large regions of memory
111 // unintentionally when we could use small two watchpoints. e.g.
112 // user_addr 0x3ff8 user_size 32
113 // can be watched with four 8-byte watchpoints or if it's done with one
114 // MASK watchpoint, it would need to be a 32KB watchpoint (a 16KB
115 // watchpoint at 0x0 only covers 0x0000-0x4000). A user request
116 // at the end of a power-of-2 region can lead to these undesirably
117 // large watchpoints and many false positive hits to ignore.
118 if (max_byte_size >= (aligned_size << 1)) {
119 aligned_size <<= 1;
120 aligned_start = user_addr & ~(aligned_size - 1);
121 if (aligned_size <= max_byte_size &&
122 aligned_start + aligned_size >= user_addr + user_size)
123 return {{.addr: aligned_start, .size: aligned_size}};
124
125 // Go back to our original aligned size, to try the multiple
126 // watchpoint approach.
127 aligned_size >>= 1;
128 }
129
130 // We need to split the user's watchpoint into two or more watchpoints
131 // that can be monitored by hardware, because of alignment and/or size
132 // reasons.
133 aligned_size = std::min(a: aligned_size, b: max_byte_size);
134 aligned_start = user_addr & ~(aligned_size - 1);
135
136 std::vector<Region> result;
137 addr_t current_address = aligned_start;
138 const addr_t user_end_address = user_addr + user_size;
139 while (current_address + aligned_size < user_end_address) {
140 result.push_back(x: {.addr: current_address, .size: aligned_size});
141 current_address += aligned_size;
142 }
143
144 if (current_address < user_end_address)
145 result.push_back(x: {.addr: current_address, .size: aligned_size});
146
147 return result;
148}
149

source code of lldb/source/Breakpoint/WatchpointAlgorithms.cpp