1 2 /* 3 * Copyright 2012 The Android Open Source Project 4 * 5 * Use of this source code is governed by a BSD-style license that can be 6 * found in the LICENSE file. 7 */ 8 9 #include "SkUtilsArm.h" 10 11 #if SK_ARM_NEON_IS_DYNAMIC 12 13 #include <unistd.h> 14 #include <fcntl.h> 15 #include <errno.h> 16 #include <string.h> 17 #include <pthread.h> 18 19 // Set USE_ANDROID_NDK_CPU_FEATURES to use the Android NDK's 20 // cpu-features helper library to detect NEON at runtime. See 21 // http://crbug.com/164154 to see why this is needed in Chromium 22 // for Android. 23 #if defined(SK_BUILD_FOR_ANDROID) 24 # define USE_ANDROID_NDK_CPU_FEATURES 1 25 #else 26 # define USE_ANDROID_NDK_CPU_FEATURES 0 27 #endif 28 29 #if USE_ANDROID_NDK_CPU_FEATURES 30 # include <cpu-features.h> 31 #endif 32 33 // Set NEON_DEBUG to 1 to allow debugging of the CPU features probing. 34 // For now, we always set it for SK_DEBUG builds. 35 #ifdef SK_DEBUG 36 # define NEON_DEBUG 1 37 #else 38 # define NEON_DEBUG 0 39 #endif 40 41 #if NEON_DEBUG 42 # ifdef SK_BUILD_FOR_ANDROID 43 // used to declare PROP_VALUE_MAX and __system_property_get() 44 # include <sys/system_properties.h> 45 # endif 46 #endif 47 48 // A function used to determine at runtime if the target CPU supports 49 // the ARM NEON instruction set. This implementation is Linux-specific. 50 static bool sk_cpu_arm_check_neon(void) { 51 bool result = false; 52 53 #if NEON_DEBUG 54 // Allow forcing the mode through the environment during debugging. 55 # ifdef SK_BUILD_FOR_ANDROID 56 // On Android, we use a system property 57 # define PROP_NAME "debug.skia.arm_neon_mode" 58 char prop[PROP_VALUE_MAX]; 59 if (__system_property_get(PROP_NAME, prop) > 0) { 60 # else 61 # define PROP_NAME "SKIA_ARM_NEON_MODE" 62 // On ARM Linux, we use an environment variable 63 const char* prop = getenv(PROP_NAME); 64 if (prop != NULL) { 65 # endif 66 SkDebugf("%s: %s", PROP_NAME, prop); 67 if (!strcmp(prop, "1")) { 68 SkDebugf("Forcing ARM Neon mode to full!\n"); 69 return true; 70 } 71 if (!strcmp(prop, "0")) { 72 SkDebugf("Disabling ARM NEON mode\n"); 73 return false; 74 } 75 } 76 SkDebugf("Running dynamic CPU feature detection\n"); 77 #endif 78 79 #if USE_ANDROID_NDK_CPU_FEATURES 80 81 result = (android_getCpuFeatures() & ANDROID_CPU_ARM_FEATURE_NEON) != 0; 82 83 #else // USE_ANDROID_NDK_CPU_FEATURES 84 85 // There is no user-accessible CPUID instruction on ARM that we can use. 86 // Instead, we must parse /proc/cpuinfo and look for the 'neon' feature. 87 // For example, here's a typical output (Nexus S running ICS 4.0.3): 88 /* 89 Processor : ARMv7 Processor rev 2 (v7l) 90 BogoMIPS : 994.65 91 Features : swp half thumb fastmult vfp edsp thumbee neon vfpv3 92 CPU implementer : 0x41 93 CPU architecture: 7 94 CPU variant : 0x2 95 CPU part : 0xc08 96 CPU revision : 2 97 98 Hardware : herring 99 Revision : 000b 100 Serial : 3833c77d6dc000ec 101 */ 102 char buffer[4096]; 103 104 // If we fail any of the following, assume we don't have NEON instructions 105 // This allows us to return immediately in case of error. 106 result = false; 107 108 do { 109 // open /proc/cpuinfo 110 int fd = TEMP_FAILURE_RETRY(open("/proc/cpuinfo", O_RDONLY)); 111 if (fd < 0) { 112 SkDebugf("Could not open /proc/cpuinfo: %s\n", strerror(errno)); 113 break; 114 } 115 116 // Read the file. To simplify our search, we're going to place two 117 // sentinel '\n' characters: one at the start of the buffer, and one at 118 // the end. This means we reserve the first and last buffer bytes. 119 buffer[0] = '\n'; 120 int size = TEMP_FAILURE_RETRY(read(fd, buffer+1, sizeof(buffer)-2)); 121 close(fd); 122 123 if (size < 0) { // should not happen 124 SkDebugf("Could not read /proc/cpuinfo: %s\n", strerror(errno)); 125 break; 126 } 127 128 SkDebugf("START /proc/cpuinfo:\n%.*s\nEND /proc/cpuinfo\n", 129 size, buffer+1); 130 131 // Compute buffer limit, and place final sentinel 132 char* buffer_end = buffer + 1 + size; 133 buffer_end[0] = '\n'; 134 135 // Now, find a line that starts with "Features", i.e. look for 136 // '\nFeatures ' in our buffer. 137 const char features[] = "\nFeatures\t"; 138 const size_t features_len = sizeof(features)-1; 139 140 char* line = (char*) memmem(buffer, buffer_end - buffer, 141 features, features_len); 142 if (line == NULL) { // Weird, no Features line, bad kernel? 143 SkDebugf("Could not find a line starting with 'Features'" 144 "in /proc/cpuinfo ?\n"); 145 break; 146 } 147 148 line += features_len; // Skip the "\nFeatures\t" prefix 149 150 // Find the end of the current line 151 char* line_end = (char*) memchr(line, '\n', buffer_end - line); 152 if (line_end == NULL) 153 line_end = buffer_end; 154 155 // Now find an instance of 'neon' in the flags list. We want to 156 // ensure it's only 'neon' and not something fancy like 'noneon' 157 // so check that it follows a space. 158 const char neon[] = " neon"; 159 const size_t neon_len = sizeof(neon)-1; 160 const char* flag = (const char*) memmem(line, line_end - line, 161 neon, neon_len); 162 if (flag == NULL) 163 break; 164 165 // Ensure it is followed by a space or a newline. 166 if (flag[neon_len] != ' ' && flag[neon_len] != '\n') 167 break; 168 169 // Fine, we support Arm NEON ! 170 result = true; 171 172 } while (0); 173 174 #endif // USE_ANDROID_NDK_CPU_FEATURES 175 176 if (result) { 177 SkDebugf("Device supports ARM NEON instructions!\n"); 178 } else { 179 SkDebugf("Device does NOT support ARM NEON instructions!\n"); 180 } 181 return result; 182 } 183 184 static pthread_once_t sOnce; 185 static bool sHasArmNeon; 186 187 // called through pthread_once() 188 void sk_cpu_arm_probe_features(void) { 189 sHasArmNeon = sk_cpu_arm_check_neon(); 190 } 191 192 bool sk_cpu_arm_has_neon(void) { 193 pthread_once(&sOnce, sk_cpu_arm_probe_features); 194 return sHasArmNeon; 195 } 196 197 #endif // SK_ARM_NEON_IS_DYNAMIC 198
