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//===-- WatchpointAlgorithms.cpp ------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "lldb/Breakpoint/WatchpointAlgorithms.h"
#include "lldb/Breakpoint/WatchpointResource.h"
#include "lldb/Target/Process.h"
#include "lldb/Utility/ArchSpec.h"
#include "lldb/Utility/LLDBLog.h"
#include "lldb/Utility/Log.h"
#include <algorithm>
#include <utility>
#include <vector>
using namespace lldb;
using namespace lldb_private;
std::vector<WatchpointResourceSP>
WatchpointAlgorithms::AtomizeWatchpointRequest(
addr_t addr, size_t size, bool read, bool write,
WatchpointHardwareFeature supported_features, ArchSpec &arch) {
std::vector<Region> entries;
if (supported_features & eWatchpointHardwareArmMASK) {
entries =
PowerOf2Watchpoints(addr, size,
/*min_byte_size*/ 1,
/*max_byte_size*/ INT32_MAX,
/*address_byte_size*/ arch.GetAddressByteSize());
} else {
// As a fallback, assume we can watch any power-of-2
// number of bytes up through the size of an address in the target.
entries =
PowerOf2Watchpoints(addr, size,
/*min_byte_size*/ 1,
/*max_byte_size*/ arch.GetAddressByteSize(),
/*address_byte_size*/ arch.GetAddressByteSize());
}
Log *log = GetLog(LLDBLog::Watchpoints);
LLDB_LOGV(log, "AtomizeWatchpointRequest user request addr {0:x} size {1}",
addr, size);
std::vector<WatchpointResourceSP> resources;
for (Region &ent : entries) {
LLDB_LOGV(log, "AtomizeWatchpointRequest creating resource {0:x} size {1}",
ent.addr, ent.size);
WatchpointResourceSP wp_res_sp =
std::make_shared<WatchpointResource>(ent.addr, ent.size, read, write);
resources.push_back(wp_res_sp);
}
return resources;
}
// This should be `std::bit_ceil(aligned_size)` but
// that requires C++20.
// Calculates the smallest integral power of two that is not smaller than x.
static uint64_t bit_ceil(uint64_t input) {
if (input <= 1 || llvm::popcount(input) == 1)
return input;
return 1ULL << (64 - llvm::countl_zero(input));
}
/// Convert a user's watchpoint request (\a user_addr and \a user_size)
/// into hardware watchpoints, for a target that can watch a power-of-2
/// region of memory (1, 2, 4, 8, etc), aligned to that same power-of-2
/// memory address.
///
/// If a user asks to watch 4 bytes at address 0x1002 (0x1002-0x1005
/// inclusive) we can implement this with two 2-byte watchpoints
/// (0x1002 and 0x1004) or with an 8-byte watchpoint at 0x1000.
/// A 4-byte watchpoint at 0x1002 would not be properly 4 byte aligned.
///
/// If a user asks to watch 16 bytes at 0x1000, and this target supports
/// 8-byte watchpoints, we can implement this with two 8-byte watchpoints
/// at 0x1000 and 0x1008.
std::vector<WatchpointAlgorithms::Region>
WatchpointAlgorithms::PowerOf2Watchpoints(addr_t user_addr, size_t user_size,
size_t min_byte_size,
size_t max_byte_size,
uint32_t address_byte_size) {
Log *log = GetLog(LLDBLog::Watchpoints);
LLDB_LOGV(log,
"AtomizeWatchpointRequest user request addr {0:x} size {1} "
"min_byte_size {2}, max_byte_size {3}, address_byte_size {4}",
user_addr, user_size, min_byte_size, max_byte_size,
address_byte_size);
// Can't watch zero bytes.
if (user_size == 0)
return {};
size_t aligned_size = std::max(user_size, min_byte_size);
/// Round up \a user_size to the next power-of-2 size
/// user_size == 8 -> aligned_size == 8
/// user_size == 9 -> aligned_size == 16
aligned_size = bit_ceil(aligned_size);
addr_t aligned_start = user_addr & ~(aligned_size - 1);
// Does this power-of-2 memory range, aligned to power-of-2 that the
// hardware can watch, completely cover the requested region.
if (aligned_size <= max_byte_size &&
aligned_start + aligned_size >= user_addr + user_size)
return {{aligned_start, aligned_size}};
// If the maximum region we can watch is larger than the aligned
// size, try increasing the region size by one power of 2 and see
// if aligning to that amount can cover the requested region.
//
// Increasing the aligned_size repeatedly instead of splitting the
// watchpoint can result in us watching large regions of memory
// unintentionally when we could use small two watchpoints. e.g.
// user_addr 0x3ff8 user_size 32
// can be watched with four 8-byte watchpoints or if it's done with one
// MASK watchpoint, it would need to be a 32KB watchpoint (a 16KB
// watchpoint at 0x0 only covers 0x0000-0x4000). A user request
// at the end of a power-of-2 region can lead to these undesirably
// large watchpoints and many false positive hits to ignore.
if (max_byte_size >= (aligned_size << 1)) {
aligned_size <<= 1;
aligned_start = user_addr & ~(aligned_size - 1);
if (aligned_size <= max_byte_size &&
aligned_start + aligned_size >= user_addr + user_size)
return {{aligned_start, aligned_size}};
// Go back to our original aligned size, to try the multiple
// watchpoint approach.
aligned_size >>= 1;
}
// We need to split the user's watchpoint into two or more watchpoints
// that can be monitored by hardware, because of alignment and/or size
// reasons.
aligned_size = std::min(aligned_size, max_byte_size);
aligned_start = user_addr & ~(aligned_size - 1);
std::vector<Region> result;
addr_t current_address = aligned_start;
const addr_t user_end_address = user_addr + user_size;
while (current_address + aligned_size < user_end_address) {
result.push_back({current_address, aligned_size});
current_address += aligned_size;
}
if (current_address < user_end_address)
result.push_back({current_address, aligned_size});
return result;
}
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