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 "private/bionic_globals.h" 18 #include "private/bionic_vdso.h" 19 20 #if defined(__aarch64__) || defined(__x86_64__) || defined (__i386__) 21 22 #include <limits.h> 23 #include <link.h> 24 #include <string.h> 25 #include <sys/cdefs.h> 26 #include <sys/time.h> 27 #include <time.h> 28 #include <unistd.h> 29 #include "private/KernelArgumentBlock.h" 30 31 int clock_gettime(int clock_id, timespec* tp) { 32 auto vdso_clock_gettime = reinterpret_cast<decltype(&clock_gettime)>( 33 __libc_globals->vdso[VDSO_CLOCK_GETTIME].fn); 34 if (__predict_true(vdso_clock_gettime)) { 35 return vdso_clock_gettime(clock_id, tp); 36 } 37 return __clock_gettime(clock_id, tp); 38 } 39 40 int gettimeofday(timeval* tv, struct timezone* tz) { 41 auto vdso_gettimeofday = reinterpret_cast<decltype(&gettimeofday)>( 42 __libc_globals->vdso[VDSO_GETTIMEOFDAY].fn); 43 if (__predict_true(vdso_gettimeofday)) { 44 return vdso_gettimeofday(tv, tz); 45 } 46 return __gettimeofday(tv, tz); 47 } 48 49 void __libc_init_vdso(libc_globals* globals, KernelArgumentBlock& args) { 50 auto&& vdso = globals->vdso; 51 vdso[VDSO_CLOCK_GETTIME] = { VDSO_CLOCK_GETTIME_SYMBOL, 52 reinterpret_cast<void*>(__clock_gettime) }; 53 vdso[VDSO_GETTIMEOFDAY] = { VDSO_GETTIMEOFDAY_SYMBOL, 54 reinterpret_cast<void*>(__gettimeofday) }; 55 56 // Do we have a vdso? 57 uintptr_t vdso_ehdr_addr = args.getauxval(AT_SYSINFO_EHDR); 58 ElfW(Ehdr)* vdso_ehdr = reinterpret_cast<ElfW(Ehdr)*>(vdso_ehdr_addr); 59 if (vdso_ehdr == nullptr) { 60 return; 61 } 62 63 // How many symbols does it have? 64 size_t symbol_count = 0; 65 ElfW(Shdr)* vdso_shdr = reinterpret_cast<ElfW(Shdr)*>(vdso_ehdr_addr + vdso_ehdr->e_shoff); 66 for (size_t i = 0; i < vdso_ehdr->e_shnum; ++i) { 67 if (vdso_shdr[i].sh_type == SHT_DYNSYM) { 68 symbol_count = vdso_shdr[i].sh_size / sizeof(ElfW(Sym)); 69 } 70 } 71 if (symbol_count == 0) { 72 return; 73 } 74 75 // Where's the dynamic table? 76 ElfW(Addr) vdso_addr = 0; 77 ElfW(Dyn)* vdso_dyn = nullptr; 78 ElfW(Phdr)* vdso_phdr = reinterpret_cast<ElfW(Phdr)*>(vdso_ehdr_addr + vdso_ehdr->e_phoff); 79 for (size_t i = 0; i < vdso_ehdr->e_phnum; ++i) { 80 if (vdso_phdr[i].p_type == PT_DYNAMIC) { 81 vdso_dyn = reinterpret_cast<ElfW(Dyn)*>(vdso_ehdr_addr + vdso_phdr[i].p_offset); 82 } else if (vdso_phdr[i].p_type == PT_LOAD) { 83 vdso_addr = vdso_ehdr_addr + vdso_phdr[i].p_offset - vdso_phdr[i].p_vaddr; 84 } 85 } 86 if (vdso_addr == 0 || vdso_dyn == nullptr) { 87 return; 88 } 89 90 // Where are the string and symbol tables? 91 const char* strtab = nullptr; 92 ElfW(Sym)* symtab = nullptr; 93 for (ElfW(Dyn)* d = vdso_dyn; d->d_tag != DT_NULL; ++d) { 94 if (d->d_tag == DT_STRTAB) { 95 strtab = reinterpret_cast<const char*>(vdso_addr + d->d_un.d_ptr); 96 } else if (d->d_tag == DT_SYMTAB) { 97 symtab = reinterpret_cast<ElfW(Sym)*>(vdso_addr + d->d_un.d_ptr); 98 } 99 } 100 if (strtab == nullptr || symtab == nullptr) { 101 return; 102 } 103 104 // Are there any symbols we want? 105 for (size_t i = 0; i < symbol_count; ++i) { 106 for (size_t j = 0; j < VDSO_END; ++j) { 107 if (strcmp(vdso[j].name, strtab + symtab[i].st_name) == 0) { 108 vdso[j].fn = reinterpret_cast<void*>(vdso_addr + symtab[i].st_value); 109 } 110 } 111 } 112 } 113 114 #else 115 116 void __libc_init_vdso(libc_globals*, KernelArgumentBlock&) { 117 } 118 119 #endif 120
