1 //===- SectionPriorities.h --------------------------------------*- C++ -*-===// 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 #ifndef LLD_MACHO_SECTION_PRIORITIES_H 10 #define LLD_MACHO_SECTION_PRIORITIES_H 11 12 #include "InputSection.h" 13 #include "llvm/ADT/DenseMap.h" 14 15 namespace lld::macho { 16 17 using SectionPair = std::pair<const InputSection *, const InputSection *>; 18 19 class PriorityBuilder { 20 public: 21 // Reads every input section's call graph profile, and combines them into 22 // callGraphProfile. If an order file is present, any edges where one or both 23 // of the vertices are specified in the order file are discarded. 24 void extractCallGraphProfile(); 25 26 // Reads the order file at `path` into config->priorities. 27 // 28 // An order file has one entry per line, in the following format: 29 // 30 // <cpu>:<object file>:<symbol name> 31 // 32 // <cpu> and <object file> are optional. If not specified, then that entry 33 // matches any symbol of that name. Parsing this format is not quite 34 // straightforward because the symbol name itself can contain colons, so when 35 // encountering a colon, we consider the preceding characters to decide if it 36 // can be a valid CPU type or file path. 37 // 38 // If a symbol is matched by multiple entries, then it takes the 39 // lowest-ordered entry (the one nearest to the front of the list.) 40 // 41 // The file can also have line comments that start with '#'. 42 void parseOrderFile(StringRef path); 43 44 // Returns layout priorities for some or all input sections. Sections are laid 45 // out in decreasing order; that is, a higher priority section will be closer 46 // to the beginning of its output section. 47 // 48 // If either an order file or a call graph profile are present, this is used 49 // as the source of priorities. If both are present, the order file takes 50 // precedence, but the call graph profile is still used for symbols that don't 51 // appear in the order file. If neither is present, an empty map is returned. 52 // 53 // Each section gets assigned the priority of the highest-priority symbol it 54 // contains. 55 llvm::DenseMap<const InputSection *, size_t> buildInputSectionPriorities(); 56 57 private: 58 // The symbol with the highest priority should be ordered first in the output 59 // section (modulo input section contiguity constraints). Using priority 60 // (highest first) instead of order (lowest first) has the convenient property 61 // that the default-constructed zero priority -- for symbols/sections without 62 // a user-defined order -- naturally ends up putting them at the end of the 63 // output. 64 struct SymbolPriorityEntry { 65 // The priority given to a matching symbol, regardless of which object file 66 // it originated from. 67 size_t anyObjectFile = 0; 68 // The priority given to a matching symbol from a particular object file. 69 llvm::DenseMap<llvm::StringRef, size_t> objectFiles; 70 }; 71 72 std::optional<size_t> getSymbolPriority(const Defined *sym); 73 llvm::DenseMap<llvm::StringRef, SymbolPriorityEntry> priorities; 74 llvm::MapVector<SectionPair, uint64_t> callGraphProfile; 75 }; 76 77 extern PriorityBuilder priorityBuilder; 78 } // namespace lld::macho 79 80 #endif 81