mozglue/build/arm.cpp

   1 /* This Source Code Form is subject to the terms of the Mozilla Public
   2  * License, v. 2.0. If a copy of the MPL was not distributed with this
   3  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   4
   5 /* compile-time and runtime tests for whether to use various ARM extensions */
   6
   7 #include "arm.h"
   8
   9 #if defined(MOZILLA_ARM_HAVE_CPUID_DETECTION)
  10
  11 // arm.h has parallel #ifs which declare MOZILLA_ARM_HAVE_CPUID_DETECTION.
  12 // We don't check it here so that we get compile errors if it's defined, but
  13 // we don't compile one of these detection methods. The detection code here is
  14 // based on the CPU detection in libtheora.
  15
  16 #  if defined(__linux__) || defined(ANDROID)
  17 #    include <stdio.h>
  18 #    include <stdlib.h>
  19 #    include <string.h>
  20
  21 enum {
  22   MOZILLA_HAS_EDSP_FLAG = 1,
  23   MOZILLA_HAS_ARMV6_FLAG = 2,
  24   MOZILLA_HAS_ARMV7_FLAG = 4,
  25   MOZILLA_HAS_NEON_FLAG = 8
  26 };
  27
  28 static unsigned get_arm_cpu_flags(void) {
  29   unsigned flags;
  30   FILE* fin;
  31   bool armv6_processor = false;
  32   flags = 0;
  33   /*Reading /proc/self/auxv would be easier, but that doesn't work reliably on
  34     Android. This also means that detection will fail in Scratchbox, which is
  35     desirable, as NEON does not work in the qemu shipped with the Maemo 5 SDK.
  36     I don't know if /proc/self/auxv would do any better in that case, anyway,
  37     or if it would return random flags from the host CPU.*/
  38   fin = fopen("/proc/cpuinfo", "r");
  39   if (fin != nullptr) {
  40     /*512 should be enough for anybody (it's even enough for all the flags that
  41       x86 has accumulated... so far).*/
  42     char buf[512];
  43     while (fgets(buf, 511, fin) != nullptr) {
  44       if (memcmp(buf, "Features", 8) == 0) {
  45         char* p;
  46         p = strstr(buf, " edsp");
  47         if (p != nullptr && (p[5] == ' ' || p[5] == '\n'))
  48           flags |= MOZILLA_HAS_EDSP_FLAG;
  49         p = strstr(buf, " neon");
  50         if (p != nullptr && (p[5] == ' ' || p[5] == '\n'))
  51           flags |= MOZILLA_HAS_NEON_FLAG;
  52       }
  53       if (memcmp(buf, "CPU architecture:", 17) == 0) {
  54         int version;
  55         version = atoi(buf + 17);
  56         if (version >= 6) flags |= MOZILLA_HAS_ARMV6_FLAG;
  57         if (version >= 7) flags |= MOZILLA_HAS_ARMV7_FLAG;
  58       }
  59       /* media/webrtc/trunk/src/system_wrappers/source/cpu_features_arm.c
  60        * Unfortunately, it seems that certain ARMv6-based CPUs
  61        * report an incorrect architecture number of 7!
  62        *
  63        * We try to correct this by looking at the 'elf_format'
  64        * field reported by the 'Processor' field, which is of the
  65        * form of "(v7l)" for an ARMv7-based CPU, and "(v6l)" for
  66        * an ARMv6-one.
  67        */
  68       if (memcmp(buf, "Processor\t:", 11) == 0) {
  69         if (strstr(buf, "(v6l)") != 0) {
  70           armv6_processor = true;
  71         }
  72       }
  73     }
  74     fclose(fin);
  75   }
  76   if (armv6_processor) {
  77     // ARMv6 pretending to be ARMv7? clear flag
  78     if (flags & MOZILLA_HAS_ARMV7_FLAG) {
  79       flags &= ~MOZILLA_HAS_ARMV7_FLAG;
  80     }
  81   }
  82   return flags;
  83 }
  84
  85 // Cache a local copy so we only have to read /proc/cpuinfo once.
  86 static unsigned arm_cpu_flags = get_arm_cpu_flags();
  87
  88 #    if !defined(MOZILLA_PRESUME_EDSP)
  89 static bool check_edsp(void) {
  90   return (arm_cpu_flags & MOZILLA_HAS_EDSP_FLAG) != 0;
  91 }
  92 #    endif
  93
  94 #    if !defined(MOZILLA_PRESUME_ARMV6)
  95 static bool check_armv6(void) {
  96   return (arm_cpu_flags & MOZILLA_HAS_ARMV6_FLAG) != 0;
  97 }
  98 #    endif
  99
 100 #    if !defined(MOZILLA_PRESUME_ARMV7)
 101 static bool check_armv7(void) {
 102   return (arm_cpu_flags & MOZILLA_HAS_ARMV7_FLAG) != 0;
 103 }
 104 #    endif
 105
 106 #    if !defined(MOZILLA_PRESUME_NEON)
 107 static bool check_neon(void) {
 108   return (arm_cpu_flags & MOZILLA_HAS_NEON_FLAG) != 0;
 109 }
 110 #    endif
 111
 112 #  endif  // defined(__linux__) || defined(ANDROID)
 113
 114 namespace mozilla {
 115 namespace arm_private {
 116 #  if !defined(MOZILLA_PRESUME_EDSP)
 117 bool edsp_enabled = check_edsp();
 118 #  endif
 119 #  if !defined(MOZILLA_PRESUME_ARMV6)
 120 bool armv6_enabled = check_armv6();
 121 #  endif
 122 #  if !defined(MOZILLA_PRESUME_ARMV7)
 123 bool armv7_enabled = check_armv7();
 124 #  endif
 125 #  if !defined(MOZILLA_PRESUME_NEON)
 126 bool neon_enabled = check_neon();
 127 #  endif
 128 }  // namespace arm_private
 129 }  // namespace mozilla
 130
 131 #endif  // MOZILLA_ARM_HAVE_CPUID_DETECTION