| 1 | //===- SectionPriorities.h --------------------------------------*- C++ -*-===// |
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| 2 | // |
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| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
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| 4 | // See https://llvm.org/LICENSE.txt for license information. |
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| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
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| 6 | // |
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| 7 | //===----------------------------------------------------------------------===// |
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| 8 | |
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| 9 | #ifndef LLD_MACHO_SECTION_PRIORITIES_H |
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| 10 | #define LLD_MACHO_SECTION_PRIORITIES_H |
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| 11 | |
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| 12 | #include "InputSection.h" |
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| 13 | #include "llvm/ADT/DenseMap.h" |
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| 14 | #include "llvm/ADT/MapVector.h" |
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| 15 | |
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| 16 | namespace lld::macho { |
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| 17 | |
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| 18 | using SectionPair = std::pair<const InputSection *, const InputSection *>; |
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| 19 | using StringPiecePair = std::pair<CStringInputSection *, size_t>; |
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| 20 | |
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| 21 | class PriorityBuilder { |
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| 22 | public: |
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| 23 | // Reads every input section's call graph profile, and combines them into |
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| 24 | // callGraphProfile. If an order file is present, any edges where one or both |
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| 25 | // of the vertices are specified in the order file are discarded. |
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| 26 | void (); |
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| 27 | |
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| 28 | // Reads the order file at `path` into config->priorities. |
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| 29 | // |
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| 30 | // An order file has one entry per line, in the following format: |
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| 31 | // |
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| 32 | // <cpu>:<object file>:[<symbol name> | CStringEntryPrefix <cstring hash>] |
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| 33 | // |
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| 34 | // <cpu> and <object file> are optional. |
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| 35 | // If not specified, then that entry tries to match either, |
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| 36 | // |
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| 37 | // 1) any symbol of the <symbol name>; |
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| 38 | // Parsing this format is not quite straightforward because the symbol name |
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| 39 | // itself can contain colons, so when encountering a colon, we consider the |
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| 40 | // preceding characters to decide if it can be a valid CPU type or file path. |
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| 41 | // If a symbol is matched by multiple entries, then it takes the |
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| 42 | // lowest-ordered entry (the one nearest to the front of the list.) |
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| 43 | // |
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| 44 | // or 2) any cstring literal with the given hash, if the entry has the |
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| 45 | // CStringEntryPrefix prefix defined below in the file. <cstring hash> is the |
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| 46 | // hash of cstring literal content. |
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| 47 | // |
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| 48 | // Cstring literals are not symbolized, we can't identify them by name |
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| 49 | // However, cstrings are deduplicated, hence unique, so we use the hash of |
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| 50 | // the content of cstring literals to identify them and assign priority to it. |
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| 51 | // We use the same hash as used in StringPiece, i.e. 31 bit: |
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| 52 | // xxh3_64bits(string) & 0x7fffffff |
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| 53 | // |
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| 54 | // The file can also have line comments that start with '#'. |
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| 55 | void parseOrderFile(StringRef path); |
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| 56 | |
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| 57 | // Returns layout priorities for some or all input sections. Sections are laid |
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| 58 | // out in decreasing order; that is, a higher priority section will be closer |
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| 59 | // to the beginning of its output section. |
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| 60 | // |
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| 61 | // If either an order file or a call graph profile are present, this is used |
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| 62 | // as the source of priorities. If both are present, the order file takes |
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| 63 | // precedence, but the call graph profile is still used for symbols that don't |
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| 64 | // appear in the order file. If neither is present, an empty map is returned. |
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| 65 | // |
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| 66 | // Each section gets assigned the priority of the highest-priority symbol it |
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| 67 | // contains. |
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| 68 | llvm::DenseMap<const InputSection *, int> buildInputSectionPriorities(); |
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| 69 | std::vector<StringPiecePair> |
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| 70 | buildCStringPriorities(ArrayRef<CStringInputSection *>); |
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| 71 | |
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| 72 | private: |
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| 73 | // The symbol with the smallest priority should be ordered first in the output |
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| 74 | // section (modulo input section contiguity constraints). |
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| 75 | struct SymbolPriorityEntry { |
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| 76 | // The priority given to a matching symbol, regardless of which object file |
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| 77 | // it originated from. |
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| 78 | int anyObjectFile = 0; |
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| 79 | // The priority given to a matching symbol from a particular object file. |
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| 80 | llvm::DenseMap<llvm::StringRef, int> objectFiles; |
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| 81 | }; |
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| 82 | const llvm::StringRef CStringEntryPrefix = "CSTR;" ; |
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| 83 | |
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| 84 | std::optional<int> getSymbolPriority(const Defined *sym); |
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| 85 | std::optional<int> getSymbolOrCStringPriority(const StringRef key, |
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| 86 | InputFile *f); |
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| 87 | llvm::DenseMap<llvm::StringRef, SymbolPriorityEntry> priorities; |
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| 88 | llvm::MapVector<SectionPair, uint64_t> callGraphProfile; |
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| 89 | }; |
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| 90 | |
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| 91 | extern PriorityBuilder priorityBuilder; |
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| 92 | } // namespace lld::macho |
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| 93 | |
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| 94 | #endif |
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| 95 | |
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