1 page.title=Understanding 64-bit Builds 2 @jd:body 3 4 <!-- 5 Copyright 2015 The Android Open Source Project 6 7 Licensed under the Apache License, Version 2.0 (the "License"); 8 you may not use this file except in compliance with the License. 9 You may obtain a copy of the License at 10 11 http://www.apache.org/licenses/LICENSE-2.0 12 13 Unless required by applicable law or agreed to in writing, software 14 distributed under the License is distributed on an "AS IS" BASIS, 15 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 16 See the License for the specific language governing permissions and 17 limitations under the License. 18 --> 19 <div id="qv-wrapper"> 20 <div id="qv"> 21 <h2>In this document</h2> 22 <ol id="auto-toc"> 23 </ol> 24 </div> 25 </div> 26 27 <h2 id=overview>Overview</h2> 28 29 <p>From the build systems perspective, the most prominent change is that now it 30 supports building binaries for two target CPU architectures (64-bit and 32-bit) 31 in the same build. Thats also known as <em>Multilib build</em>.</p> 32 33 <p>For native static libraries and shared libraries, the build system sets up 34 rules to build binaries for both architectures. The product configuration 35 (PRODUCT_PACKAGES), together with the dependency graph, determines which 36 binaries are built and installed to the system image.</p> 37 38 <p>For executables and apps, the build system builds only the 64-bit version by 39 default, but you can override this setting by using a global 40 <code>BoardConfig.mk</code> variable or a module-scoped variable.</p> 41 42 <p class="caution"><strong>Caution:</strong> If an app exposes an API to other 43 apps that can be either 32- or 64-bit, the app must have the 44 <code>android:multiarch</code> property set to a value of <code>true</code> 45 within its manifest to avoid potential errors.</p> 46 47 <h2 id=product_configuration>Product Configuration</h2> 48 49 50 <p>In <code>BoardConfig.mk</code>, we added the following variables to 51 configure the second CPU architecture and ABI:</p> 52 53 <pre class=prettyprint> 54 TARGET_2ND_ARCH 55 TARGET_2ND_ARCH_VARIANT 56 TARGET_2ND_CPU_VARIANT 57 TARGET_2ND_CPU_ABI 58 TARGET_2ND_CPU_ABI2 59 </pre> 60 61 62 <p>You can see an example in <code>build/target/board/generic_arm64/BoardConfig.mk</code>.</p> 63 64 <p>If you want the build system to build 32-bit executables and apps by default, 65 set the following variable:</p> 66 67 <pre class=prettyprint> 68 TARGET_PREFER_32_BIT := true 69 </pre> 70 71 <p>However, you can override this setting by using module-specific variables in 72 <code>Android.mk</code>.</p> 73 74 <p>In a Multilib build, module names in <code>PRODUCT_PACKAGES</code> cover 75 both the 32-bit and 64-bit binaries, as long as they are defined by the build 76 system. For libraries pulled in by dependency, a 32-bit library is installed 77 only if its required by another 32-bit library or executable. The same is true 78 for 64-bit libraries.</p> 79 80 <p>However, module names on the <code>make</code> command line cover only the 81 64-bit version. For example, after running <code>lunch 82 aosp_arm64-eng</code>,<code>make libc</code> builds only the 64-bit libc. To 83 build the 32-bit libc, you need to run <code>make libc_32</code>.</p> 84 85 <h2 id=module_definition_in_android_mk>Module Definition in Android.mk</h2> 86 87 <p>You can use the <code>LOCAL_MULTILIB</code> variable to configure your build 88 for 32-bit and/or 64-bit and override the global 89 <code>TARGET_PREFER_32_BIT</code>.</p> 90 91 <p>Set <code>LOCAL_MULTILIB</code> to one of the following:</p> 92 93 <ul> 94 <li>"both: build both 32-bit and 64-bit.</li> 95 <li>32: build only 32-bit.</li> 96 <li>64: build only 64-bit.</li> 97 <li>first: build for only the first arch (32-bit in 32-bit devices and 64-bit 98 in 64-bit devices).</li> 99 <li>: the default; the build system decides what arch to build based on the 100 module class and other LOCAL_ variables, such as LOCAL_MODULE_TARGET_ARCH, 101 LOCAL_32_BIT_ONLY, etc.</li> 102 </ul> 103 104 <p>In a Multilib build, conditionals like <code>ifeq $(TARGET_ARCH)</code> dont work any 105 more. </p> 106 107 <p>If you want to build your module for some specific arch(s), the following 108 variables can help you:</p> 109 110 <ul> 111 <li>LOCAL_MODULE_TARGET_ARCH<br>It can be set to a list of archs, something 112 like arm x86 arm64. Only if the arch being built is among that list will the 113 current module be included by the build system.</li> 114 115 <li>LOCAL_MODULE_UNSUPPORTED_TARGET_ARCH<br>The opposite of 116 LOCAL_MODULE_TARGET_ARCH. Only if the arch being built is not among the list, 117 the current module will be included.</li> 118 </ul> 119 120 <p>There are minor variants of the above two variables:</p> 121 122 <ul> 123 <li>LOCAL_MODULE_TARGET_ARCH_WARN</li> 124 <li>LOCAL_MODULE_UNSUPPORTED_TARGET_ARCH_WARN</li> 125 </ul> 126 127 <p>The build system will give warning if the current module is skipped due to 128 archs limited by them.</p> 129 130 <p>To set up arch-specific build flags, use the arch-specific LOCAL_ variables. An 131 arch-specific LOCAL_ variable is a normal LOCAL_ variable with an arch suffix, 132 for example:</p> 133 134 <ul> 135 <li> <code>LOCAL_SRC_FILES_arm, LOCAL_SRC_FILES_x86,</code> 136 <li> <code>LOCAL_CFLAGS_arm, LOCAL_CFLAGS_arm64,</code> 137 <li> <code>LOCAL_LDFLAGS_arm, LOCAL_LDFLAGS_arm64,</code> 138 </ul> 139 140 <p>Those variables will be applied only if a binary is currently being built for 141 that arch.</p> 142 143 <p>Sometimes its more convenient to set up flags based on whether the binary is 144 currently being built for 32-bit or 64-bit. In that case you can use the LOCAL_ 145 variable with a _32 or _64 suffix, for example:</p> 146 147 <ul> 148 <li> <code>LOCAL_SRC_FILES_32, LOCAL_SRC_FILES_64,</code> 149 <li> <code>LOCAL_CFLAGS_32, LOCAL_CFLAGS_64,</code> 150 <li> <code>LOCAL_LDFLAGS_32, LOCAL_LDFLAGS_64,</code> 151 </ul> 152 153 <p>Note that not all of the LOCAL_ variables support the arch-specific variants. 154 For an up-to-date list of such variables, refer to <code>build/core/clear_vars.mk</code>.</p> 155 156 <h2 id=install_path>Install path</h2> 157 158 159 <p>In the past, you could use LOCAL_MODULE_PATH to install a library to a 160 location other than the default one. For example, <code>LOCAL_MODULE_PATH := 161 $(TARGET_OUT_SHARED_LIBRARIES)/hw</code>.</p> 162 163 <p>In Multilib build, use LOCAL_MODULE_RELATIVE_PATH instead:</p> 164 165 <pre class=prettyprint> 166 LOCAL_MODULE_RELATIVE_PATH := hw 167 </pre> 168 169 170 <p>so that both the 64-bit and 32-bit libraries can be installed to the right 171 place.</p> 172 173 <p>If you build an executable as both 32-bit and 64-bit, youll need to use one of 174 the following variables to distinguish the install path:</p> 175 176 <ul> 177 <li><code>LOCAL_MODULE_STEM_32, LOCAL_MODULE_STEM_64</code><br>Specifies the installed file name. 178 <li><code>LOCAL_MODULE_PATH_32, LOCAL_MODULE_PATH_64</code><br>Specifies the install path. 179 </ul> 180 181 <h2 id=generated_sources>Generated sources </h2> 182 183 <p>In a Multilib build, if you generate source files to 184 <code>$(local-intermediates-dir)</code> (or <code>$(intermediates-dir-for) 185 </code>with explicit variables), it wont reliably work any more. Thats 186 because the intermediate generated sources will be required by both 32-bit and 187 64-bit build, but <code>$(local-intermediates-dir)</code> only points to one of 188 the two intermediate directories.</p> 189 190 <p>Happily, the build system now provides a dedicated, Multilib-friendly, 191 intermediate directory for generating sources. You can call<code> 192 $(local-generated-sources-dir)</code> or 193 <code>$(generated-sources-dir-for)</code> to get the directorys path. Their 194 usages are similar to <code>$(local-intermediates-dir)</code> and 195 <code>$(intermediates-dir-for)</code>. </p> 196 197 <p>If a source file is generated to the new dedicated directory and picked up 198 by <code>LOCAL_GENERATED_SOURCES</code>, it is built for both 32-bit and 64-bit 199 in multilib build.</p> 200 201 <h2 id=prebuilts>Prebuilts</h2> 202 203 204 <p>In Multilib, you cant use <code>TARGET_ARCH</code> (or together with 205 <code>TARGET_2ND_ARCH</code>) to tell the build system what arch the prebuilt 206 binary is targeted for. Use the aforementioned <code>LOCAL_</code> variable 207 <code>LOCAL_MODULE_TARGET_ARCH</code> or 208 <code>LOCAL_MODULE_UNSUPPORTED_TARGET_ARCH</code> instead.</p> 209 210 <p>With these variables, the build system can choose the corresponding 32-bit 211 prebuilt binary even if its currently doing a 64-bit Multilib build.</p> 212 213 <p>If you want to use the chosen arch to compute the source path for the prebuilt 214 binary , you can call<code> $(get-prebuilt-src-arch)</code>.</p> 215 216 <h2 id=dex-preopt>Dex-preopt</h2> 217 218 219 <p>For 64-bit devices, by default we generate both 32-bit and 64-bit odex files 220 for the boot image and any Java libraries. For APKs, by default we generate 221 odex only for the primary 64-bit arch. If an app will be launched in both 222 32-bit and 64-bit processes, please use <code>LOCAL_MULTILIB := both</code> to make sure 223 both 32-bit and 64-bit odex files are generated. That flag also tells the build 224 system to include both 32-bit and 64-bit JNI libraries, if the app has any.</p> 225 226
