1/*
2 * Copyright 2017 The Abseil Authors.
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * https://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17// Allow dynamic symbol lookup for in-memory Elf images.
18
19#ifndef ABSL_DEBUGGING_INTERNAL_ELF_MEM_IMAGE_H_
20#define ABSL_DEBUGGING_INTERNAL_ELF_MEM_IMAGE_H_
21
22// Including this will define the __GLIBC__ macro if glibc is being
23// used.
24#include <climits>
25
26// Maybe one day we can rewrite this file not to require the elf
27// symbol extensions in glibc, but for right now we need them.
28#ifdef ABSL_HAVE_ELF_MEM_IMAGE
29#error ABSL_HAVE_ELF_MEM_IMAGE cannot be directly set
30#endif
31
32#if defined(__ELF__) && defined(__GLIBC__) && !defined(__native_client__) && \
33 !defined(__asmjs__) && !defined(__wasm__)
34#define ABSL_HAVE_ELF_MEM_IMAGE 1
35#endif
36
37#ifdef ABSL_HAVE_ELF_MEM_IMAGE
38
39#include <link.h> // for ElfW
40
41namespace absl {
42namespace debugging_internal {
43
44// An in-memory ELF image (may not exist on disk).
45class ElfMemImage {
46 private:
47 // Sentinel: there could never be an elf image at &kInvalidBaseSentinel.
48 static const int kInvalidBaseSentinel;
49
50 public:
51 // Sentinel: there could never be an elf image at this address.
52 static constexpr const void *const kInvalidBase =
53 static_cast<const void*>(&kInvalidBaseSentinel);
54
55 // Information about a single vdso symbol.
56 // All pointers are into .dynsym, .dynstr, or .text of the VDSO.
57 // Do not free() them or modify through them.
58 struct SymbolInfo {
59 const char *name; // E.g. "__vdso_getcpu"
60 const char *version; // E.g. "LINUX_2.6", could be ""
61 // for unversioned symbol.
62 const void *address; // Relocated symbol address.
63 const ElfW(Sym) *symbol; // Symbol in the dynamic symbol table.
64 };
65
66 // Supports iteration over all dynamic symbols.
67 class SymbolIterator {
68 public:
69 friend class ElfMemImage;
70 const SymbolInfo *operator->() const;
71 const SymbolInfo &operator*() const;
72 SymbolIterator& operator++();
73 bool operator!=(const SymbolIterator &rhs) const;
74 bool operator==(const SymbolIterator &rhs) const;
75 private:
76 SymbolIterator(const void *const image, int index);
77 void Update(int incr);
78 SymbolInfo info_;
79 int index_;
80 const void *const image_;
81 };
82
83
84 explicit ElfMemImage(const void *base);
85 void Init(const void *base);
86 bool IsPresent() const { return ehdr_ != nullptr; }
87 const ElfW(Phdr)* GetPhdr(int index) const;
88 const ElfW(Sym)* GetDynsym(int index) const;
89 const ElfW(Versym)* GetVersym(int index) const;
90 const ElfW(Verdef)* GetVerdef(int index) const;
91 const ElfW(Verdaux)* GetVerdefAux(const ElfW(Verdef) *verdef) const;
92 const char* GetDynstr(ElfW(Word) offset) const;
93 const void* GetSymAddr(const ElfW(Sym) *sym) const;
94 const char* GetVerstr(ElfW(Word) offset) const;
95 int GetNumSymbols() const;
96
97 SymbolIterator begin() const;
98 SymbolIterator end() const;
99
100 // Look up versioned dynamic symbol in the image.
101 // Returns false if image is not present, or doesn't contain given
102 // symbol/version/type combination.
103 // If info_out is non-null, additional details are filled in.
104 bool LookupSymbol(const char *name, const char *version,
105 int symbol_type, SymbolInfo *info_out) const;
106
107 // Find info about symbol (if any) which overlaps given address.
108 // Returns true if symbol was found; false if image isn't present
109 // or doesn't have a symbol overlapping given address.
110 // If info_out is non-null, additional details are filled in.
111 bool LookupSymbolByAddress(const void *address, SymbolInfo *info_out) const;
112
113 private:
114 const ElfW(Ehdr) *ehdr_;
115 const ElfW(Sym) *dynsym_;
116 const ElfW(Versym) *versym_;
117 const ElfW(Verdef) *verdef_;
118 const ElfW(Word) *hash_;
119 const char *dynstr_;
120 size_t strsize_;
121 size_t verdefnum_;
122 ElfW(Addr) link_base_; // Link-time base (p_vaddr of first PT_LOAD).
123};
124
125} // namespace debugging_internal
126} // namespace absl
127
128#endif // ABSL_HAVE_ELF_MEM_IMAGE
129
130#endif // ABSL_DEBUGGING_INTERNAL_ELF_MEM_IMAGE_H_
131