1/*
2 * Copyright (C) 2014 The Android Open Source Project
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 *      http://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#include <link.h>
18#include <sys/auxv.h>
19#include <unistd.h>
20
21// x86 has a vdso, but there's nothing useful to us in it.
22#if defined(__aarch64__) || defined(__x86_64__)
23
24#if defined(__aarch64__)
25#define VDSO_CLOCK_GETTIME_SYMBOL "__kernel_clock_gettime"
26#define VDSO_GETTIMEOFDAY_SYMBOL  "__kernel_gettimeofday"
27#elif defined(__x86_64__)
28#define VDSO_CLOCK_GETTIME_SYMBOL "__vdso_clock_gettime"
29#define VDSO_GETTIMEOFDAY_SYMBOL  "__vdso_gettimeofday"
30#endif
31
32#include <time.h>
33
34extern "C" int __clock_gettime(int, timespec*);
35extern "C" int __gettimeofday(timeval*, struct timezone*);
36
37struct vdso_entry {
38  const char* name;
39  void* fn;
40};
41
42enum {
43  VDSO_CLOCK_GETTIME = 0,
44  VDSO_GETTIMEOFDAY,
45  VDSO_END
46};
47
48static vdso_entry vdso_entries[] = {
49  [VDSO_CLOCK_GETTIME] = { VDSO_CLOCK_GETTIME_SYMBOL, reinterpret_cast<void*>(__clock_gettime) },
50  [VDSO_GETTIMEOFDAY] = { VDSO_GETTIMEOFDAY_SYMBOL, reinterpret_cast<void*>(__gettimeofday) },
51};
52
53int clock_gettime(int clock_id, timespec* tp) {
54  static int (*vdso_clock_gettime)(int, timespec*) =
55      (int (*)(int, timespec*)) vdso_entries[VDSO_CLOCK_GETTIME].fn;
56  return vdso_clock_gettime(clock_id, tp);
57}
58
59int gettimeofday(timeval* tv, struct timezone* tz) {
60  static int (*vdso_gettimeofday)(timeval*, struct timezone*) =
61      (int (*)(timeval*, struct timezone*)) vdso_entries[VDSO_GETTIMEOFDAY].fn;
62  return vdso_gettimeofday(tv, tz);
63}
64
65void __libc_init_vdso() {
66  // Do we have a vdso?
67  uintptr_t vdso_ehdr_addr = getauxval(AT_SYSINFO_EHDR);
68  ElfW(Ehdr)* vdso_ehdr = reinterpret_cast<ElfW(Ehdr)*>(vdso_ehdr_addr);
69  if (vdso_ehdr == NULL) {
70    return;
71  }
72
73  // How many symbols does it have?
74  size_t symbol_count = 0;
75  ElfW(Shdr)* vdso_shdr = reinterpret_cast<ElfW(Shdr)*>(vdso_ehdr_addr + vdso_ehdr->e_shoff);
76  for (size_t i = 0; i < vdso_ehdr->e_shnum; ++i) {
77    if (vdso_shdr[i].sh_type == SHT_DYNSYM) {
78      symbol_count = vdso_shdr[i].sh_size / sizeof(ElfW(Sym));
79    }
80  }
81  if (symbol_count == 0) {
82    return;
83  }
84
85  // Where's the dynamic table?
86  ElfW(Addr) vdso_addr = 0;
87  ElfW(Dyn)* vdso_dyn = NULL;
88  ElfW(Phdr)* vdso_phdr = reinterpret_cast<ElfW(Phdr)*>(vdso_ehdr_addr + vdso_ehdr->e_phoff);
89  for (size_t i = 0; i < vdso_ehdr->e_phnum; ++i) {
90    if (vdso_phdr[i].p_type == PT_DYNAMIC) {
91      vdso_dyn = reinterpret_cast<ElfW(Dyn)*>(vdso_ehdr_addr + vdso_phdr[i].p_offset);
92    } else if (vdso_phdr[i].p_type == PT_LOAD) {
93      vdso_addr = vdso_ehdr_addr + vdso_phdr[i].p_offset - vdso_phdr[i].p_vaddr;
94    }
95  }
96  if (vdso_addr == 0 || vdso_dyn == NULL) {
97    return;
98  }
99
100  // Where are the string and symbol tables?
101  const char* strtab = NULL;
102  ElfW(Sym)* symtab = NULL;
103  for (ElfW(Dyn)* d = vdso_dyn; d->d_tag != DT_NULL; ++d) {
104    if (d->d_tag == DT_STRTAB) {
105      strtab = reinterpret_cast<const char*>(vdso_addr + d->d_un.d_ptr);
106    } else if (d->d_tag == DT_SYMTAB) {
107      symtab = reinterpret_cast<ElfW(Sym)*>(vdso_addr + d->d_un.d_ptr);
108    }
109  }
110  if (strtab == NULL || symtab == NULL) {
111    return;
112  }
113
114  // Are there any symbols we want?
115  for (size_t i = 0; i < symbol_count; ++i) {
116    for (size_t j = 0; j < VDSO_END; ++j) {
117      if (strcmp(vdso_entries[j].name, strtab + symtab[i].st_name) == 0) {
118        vdso_entries[j].fn = reinterpret_cast<void*>(vdso_addr + symtab[i].st_value);
119      }
120    }
121  }
122}
123
124#else
125
126void __libc_init_vdso() {
127}
128
129#endif
130