1 //===- SymbolRewriter.h - Symbol Rewriting Pass -----------------*- 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 // This file provides the prototypes and definitions related to the Symbol
10 // Rewriter pass.
11 //
12 // The Symbol Rewriter pass takes a set of rewrite descriptors which define
13 // transformations for symbol names.  These can be either single name to name
14 // trnsformation or more broad regular expression based transformations.
15 //
16 // All the functions are re-written at the IR level.  The Symbol Rewriter itself
17 // is exposed as a module level pass.  All symbols at the module level are
18 // iterated.  For any matching symbol, the requested transformation is applied,
19 // updating references to it as well (a la RAUW).  The resulting binary will
20 // only contain the rewritten symbols.
21 //
22 // By performing this operation in the compiler, we are able to catch symbols
23 // that would otherwise not be possible to catch (e.g. inlined symbols).
24 //
25 // This makes it possible to cleanly transform symbols without resorting to
26 // overly-complex macro tricks and the pre-processor.  An example of where this
27 // is useful is the sanitizers where we would like to intercept a well-defined
28 // set of functions across the module.
29 //
30 //===----------------------------------------------------------------------===//
31 
32 #ifndef LLVM_TRANSFORMS_UTILS_SYMBOLREWRITER_H
33 #define LLVM_TRANSFORMS_UTILS_SYMBOLREWRITER_H
34 
35 #include "llvm/IR/PassManager.h"
36 #include <list>
37 #include <memory>
38 #include <string>
39 
40 namespace llvm {
41 
42 class MemoryBuffer;
43 class Module;
44 class ModulePass;
45 
46 namespace yaml {
47 
48 class KeyValueNode;
49 class MappingNode;
50 class ScalarNode;
51 class Stream;
52 
53 } // end namespace yaml
54 
55 namespace SymbolRewriter {
56 
57 /// The basic entity representing a rewrite operation.  It serves as the base
58 /// class for any rewrite descriptor.  It has a certain set of specializations
59 /// which describe a particular rewrite.
60 ///
61 /// The RewriteMapParser can be used to parse a mapping file that provides the
62 /// mapping for rewriting the symbols.  The descriptors individually describe
63 /// whether to rewrite a function, global variable, or global alias.  Each of
64 /// these can be selected either by explicitly providing a name for the ones to
65 /// be rewritten or providing a (posix compatible) regular expression that will
66 /// select the symbols to rewrite.  This descriptor list is passed to the
67 /// SymbolRewriter pass.
68 class RewriteDescriptor {
69 public:
70   enum class Type {
71     Invalid,        /// invalid
72     Function,       /// function - descriptor rewrites a function
73     GlobalVariable, /// global variable - descriptor rewrites a global variable
74     NamedAlias,     /// named alias - descriptor rewrites a global alias
75   };
76 
77   RewriteDescriptor(const RewriteDescriptor &) = delete;
78   RewriteDescriptor &operator=(const RewriteDescriptor &) = delete;
79   virtual ~RewriteDescriptor() = default;
80 
81   Type getType() const { return Kind; }
82 
83   virtual bool performOnModule(Module &M) = 0;
84 
85 protected:
86   explicit RewriteDescriptor(Type T) : Kind(T) {}
87 
88 private:
89   const Type Kind;
90 };
91 
92 using RewriteDescriptorList = std::list<std::unique_ptr<RewriteDescriptor>>;
93 
94 class RewriteMapParser {
95 public:
96   bool parse(const std::string &MapFile, RewriteDescriptorList *Descriptors);
97 
98 private:
99   bool parse(std::unique_ptr<MemoryBuffer> &MapFile, RewriteDescriptorList *DL);
100   bool parseEntry(yaml::Stream &Stream, yaml::KeyValueNode &Entry,
101                   RewriteDescriptorList *DL);
102   bool parseRewriteFunctionDescriptor(yaml::Stream &Stream,
103                                       yaml::ScalarNode *Key,
104                                       yaml::MappingNode *Value,
105                                       RewriteDescriptorList *DL);
106   bool parseRewriteGlobalVariableDescriptor(yaml::Stream &Stream,
107                                             yaml::ScalarNode *Key,
108                                             yaml::MappingNode *Value,
109                                             RewriteDescriptorList *DL);
110   bool parseRewriteGlobalAliasDescriptor(yaml::Stream &YS, yaml::ScalarNode *K,
111                                          yaml::MappingNode *V,
112                                          RewriteDescriptorList *DL);
113 };
114 
115 } // end namespace SymbolRewriter
116 
117 class RewriteSymbolPass : public PassInfoMixin<RewriteSymbolPass> {
118 public:
119   RewriteSymbolPass() { loadAndParseMapFiles(); }
120 
121   RewriteSymbolPass(SymbolRewriter::RewriteDescriptorList &DL) {
122     Descriptors.splice(Descriptors.begin(), DL);
123   }
124 
125   PreservedAnalyses run(Module &M, ModuleAnalysisManager &AM);
126 
127   // Glue for old PM
128   bool runImpl(Module &M);
129 
130 private:
131   void loadAndParseMapFiles();
132 
133   SymbolRewriter::RewriteDescriptorList Descriptors;
134 };
135 
136 } // end namespace llvm
137 
138 #endif // LLVM_TRANSFORMS_UTILS_SYMBOLREWRITER_H
139