================ @@ -0,0 +1,146 @@ +//===-- 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 <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<std::pair<addr_t, size_t>> entries; + + if (supported_features & + WatchpointHardwareFeature::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()); + } + + std::vector<WatchpointResourceSP> resources; + for (std::pair<addr_t, size_t> &ent : entries) { + addr_t addr = std::get<0>(ent); + size_t size = std::get<1>(ent); + WatchpointResourceSP wp_res_sp = + std::make_shared<WatchpointResource>(addr, size, read, write); + resources.push_back(wp_res_sp); + } + + return resources; +} + +/// 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<std::pair<addr_t, size_t>> +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) { + + // Can't watch zero bytes. + if (user_size == 0) + return {}; + + // The aligned watch region will be less than/equal to the size of + // an address in this target. + const int address_bit_size = address_byte_size * 8; + + 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 + /// user_size == 15 -> aligned_size == 16 + /// user_size == 192 -> aligned_size == 256 + /// Could be `std::bit_ceil(aligned_size)` when we build with C++20? + + aligned_size = 1ULL << (address_bit_size - __builtin_clzll(aligned_size - 1)); + + 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<std::pair<addr_t, size_t>> 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}); + } ---------------- JDevlieghere wrote:
Nit: no braces around single-line `if`s. https://github.com/llvm/llvm-project/pull/79962 _______________________________________________ lldb-commits mailing list lldb-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits
