base/os_compat_android.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "base/os_compat_android.h"
   6
   7 #include <errno.h>
   8 #include <math.h>
   9 #include <sys/stat.h>
  10 #include <time64.h>
  11
  12 #include "base/rand_util.h"
  13 #include "base/string_piece.h"
  14 #include "base/stringprintf.h"
  15
  16 // There is no futimes() avaiable in Bionic, so we provide our own
  17 // implementation until it is there.
  18 extern "C" {
  19
  20 int futimes(int fd, const struct timeval tv[2]) {
  21   const std::string fd_path = StringPrintf("/proc/self/fd/%d", fd);
  22   return utimes(fd_path.c_str(), tv);
  23 }
  24
  25 // Android has only timegm64() and no timegm().
  26 // We replicate the behaviour of timegm() when the result overflows time_t.
  27 time_t timegm(struct tm* const t) {
  28   // time_t is signed on Android.
  29   static const time_t kTimeMax = ~(1 << (sizeof(time_t) * CHAR_BIT - 1));
  30   static const time_t kTimeMin = (1 << (sizeof(time_t) * CHAR_BIT - 1));
  31   time64_t result = timegm64(t);
  32   if (result < kTimeMin || result > kTimeMax)
  33     return -1;
  34   return result;
  35 }
  36
  37 // The following is only needed when building with GCC 4.6 or higher
  38 // (i.e. not with Android GCC 4.4.3, nor with Clang).
  39 //
  40 // GCC is now capable of optimizing successive calls to sin() and cos() into
  41 // a single call to sincos(). This means that source code that looks like:
  42 //
  43 //     double c, s;
  44 //     c = cos(angle);
  45 //     s = sin(angle);
  46 //
  47 // Will generate machine code that looks like:
  48 //
  49 //     double c, s;
  50 //     sincos(angle, &s, &c);
  51 //
  52 // Unfortunately, sincos() and friends are not part of the Android libm.so
  53 // library provided by the NDK for API level 9. When the optimization kicks
  54 // in, it makes the final build fail with a puzzling message (puzzling
  55 // because 'sincos' doesn't appear anywhere in the sources!).
  56 //
  57 // To solve this, we provide our own implementation of the sincos() function
  58 // and related friends. Note that we must also explicitely tell GCC to disable
  59 // optimizations when generating these. Otherwise, the generated machine code
  60 // for each function would simply end up calling itself, resulting in a
  61 // runtime crash due to stack overflow.
  62 //
  63 #if defined(__GNUC__) && !defined(__clang__)
  64
  65 // For the record, Clang does not support the 'optimize' attribute.
  66 // In the unlikely event that it begins performing this optimization too,
  67 // we'll have to find a different way to achieve this. NOTE: Tested with O1
  68 // which still performs the optimization.
  69 //
  70 #define GCC_NO_OPTIMIZE  __attribute__((optimize("O0")))
  71
  72 GCC_NO_OPTIMIZE
  73 void sincos(double angle, double* s, double *c) {
  74   *c = cos(angle);
  75   *s = sin(angle);
  76 }
  77
  78 GCC_NO_OPTIMIZE
  79 void sincosf(float angle, float* s, float* c) {
  80   *c = cosf(angle);
  81   *s = sinf(angle);
  82 }
  83
  84 #endif // __GNUC__ && !__clang__
  85
  86 // An implementation of mkdtemp, since it is not exposed by the NDK
  87 // for native API level 9 that we target.
  88 //
  89 // For any changes in the mkdtemp function, you should manually run the unittest
  90 // OsCompatAndroidTest.DISABLED_TestMkdTemp in your local machine to check if it
  91 // passes. Please don't enable it, since it creates a directory and may be
  92 // source of flakyness.
  93 char* mkdtemp(char* path) {
  94   if (path == NULL) {
  95     errno = EINVAL;
  96     return NULL;
  97   }
  98
  99   const int path_len = strlen(path);
 100
 101   // The last six characters of 'path' must be XXXXXX.
 102   const base::StringPiece kSuffix("XXXXXX");
 103   const int kSuffixLen = kSuffix.length();
 104   if (!base::StringPiece(path, path_len).ends_with(kSuffix)) {
 105     errno = EINVAL;
 106     return NULL;
 107   }
 108
 109   // If the path contains a directory, as in /tmp/foo/XXXXXXXX, make sure
 110   // that /tmp/foo exists, otherwise we're going to loop a really long
 111   // time for nothing below
 112   char* dirsep = strrchr(path, '/');
 113   if (dirsep != NULL) {
 114     struct stat st;
 115     int ret;
 116
 117     *dirsep = '\0';  // Terminating directory path temporarily
 118
 119     ret = stat(path, &st);
 120
 121     *dirsep = '/';  // Restoring directory separator
 122     if (ret < 0)  // Directory probably does not exist
 123       return NULL;
 124     if (!S_ISDIR(st.st_mode)) {  // Not a directory
 125       errno = ENOTDIR;
 126       return NULL;
 127     }
 128   }
 129
 130   // Max number of tries using different random suffixes.
 131   const int kMaxTries = 100;
 132
 133   // Now loop until we CAN create a directory by that name or we reach the max
 134   // number of tries.
 135   for (int i = 0; i < kMaxTries; ++i) {
 136     // Fill the suffix XXXXXX with a random string composed of a-z chars.
 137     for (int pos = 0; pos < kSuffixLen; ++pos) {
 138       char rand_char = static_cast<char>(base::RandInt('a', 'z'));
 139       path[path_len - kSuffixLen + pos] = rand_char;
 140     }
 141     if (mkdir(path, 0700) == 0) {
 142       // We just created the directory succesfully.
 143       return path;
 144     }
 145     if (errno != EEXIST) {
 146       // The directory doesn't exist, but an error occured
 147       return NULL;
 148     }
 149   }
 150
 151   // We reached the max number of tries.
 152   return NULL;
 153 }
 154
 155 }  // extern "C"