1Working on bionic 2================= 3 4What are the big pieces of bionic? 5---------------------------------- 6 7#### libc/ --- libc.so, libc.a 8 9The C library. Stuff like `fopen(3)` and `kill(2)`. 10 11#### libm/ --- libm.so, libm.a 12 13The math library. Traditionally Unix systems kept stuff like `sin(3)` and 14`cos(3)` in a separate library to save space in the days before shared 15libraries. 16 17#### libdl/ --- libdl.so 18 19The dynamic linker interface library. This is actually just a bunch of stubs 20that the dynamic linker replaces with pointers to its own implementation at 21runtime. This is where stuff like `dlopen(3)` lives. 22 23#### libstdc++/ --- libstdc++.so 24 25The C++ ABI support functions. The C++ compiler doesn't know how to implement 26thread-safe static initialization and the like, so it just calls functions that 27are supplied by the system. Stuff like `__cxa_guard_acquire` and 28`__cxa_pure_virtual` live here. 29 30#### linker/ --- /system/bin/linker and /system/bin/linker64 31 32The dynamic linker. When you run a dynamically-linked executable, its ELF file 33has a `DT_INTERP` entry that says "use the following program to start me". On 34Android, that's either `linker` or `linker64` (depending on whether it's a 3532-bit or 64-bit executable). It's responsible for loading the ELF executable 36into memory and resolving references to symbols (so that when your code tries to 37jump to `fopen(3)`, say, it lands in the right place). 38 39#### tests/ --- unit tests 40 41The `tests/` directory contains unit tests. Roughly arranged as one file per 42publicly-exported header file. 43 44#### benchmarks/ --- benchmarks 45 46The `benchmarks/` directory contains benchmarks. 47 48 49What's in libc/? 50---------------- 51 52<pre> 53libc/ 54 arch-arm/ 55 arch-arm64/ 56 arch-common/ 57 arch-mips/ 58 arch-mips64/ 59 arch-x86/ 60 arch-x86_64/ 61 # Each architecture has its own subdirectory for stuff that isn't shared 62 # because it's architecture-specific. There will be a .mk file in here that 63 # drags in all the architecture-specific files. 64 bionic/ 65 # Every architecture needs a handful of machine-specific assembler files. 66 # They live here. 67 include/ 68 machine/ 69 # The majority of header files are actually in libc/include/, but many 70 # of them pull in a <machine/something.h> for things like limits, 71 # endianness, and how floating point numbers are represented. Those 72 # headers live here. 73 string/ 74 # Most architectures have a handful of optional assembler files 75 # implementing optimized versions of various routines. The <string.h> 76 # functions are particular favorites. 77 syscalls/ 78 # The syscalls directories contain script-generated assembler files. 79 # See 'Adding system calls' later. 80 81 include/ 82 # The public header files on everyone's include path. These are a mixture of 83 # files written by us and files taken from BSD. 84 85 kernel/ 86 # The kernel uapi header files. These are scrubbed copies of the originals 87 # in external/kernel-headers/. These files must not be edited directly. The 88 # generate_uapi_headers.sh script should be used to go from a kernel tree to 89 # external/kernel-headers/ --- this takes care of the architecture-specific 90 # details. The update_all.py script should be used to regenerate bionic's 91 # scrubbed headers from external/kernel-headers/. 92 93 private/ 94 # These are private header files meant for use within bionic itself. 95 96 dns/ 97 # Contains the DNS resolver (originates from NetBSD code). 98 99 upstream-freebsd/ 100 upstream-netbsd/ 101 upstream-openbsd/ 102 # These directories contain unmolested upstream source. Any time we can 103 # just use a BSD implementation of something unmodified, we should. 104 # The structure under these directories mimics the upstream tree, 105 # but there's also... 106 android/ 107 include/ 108 # This is where we keep the hacks necessary to build BSD source 109 # in our world. The *-compat.h files are automatically included 110 # using -include, but we also provide equivalents for missing 111 # header/source files needed by the BSD implementation. 112 113 bionic/ 114 # This is the biggest mess. The C++ files are files we own, typically 115 # because the Linux kernel interface is sufficiently different that we 116 # can't use any of the BSD implementations. The C files are usually 117 # legacy mess that needs to be sorted out, either by replacing it with 118 # current upstream source in one of the upstream directories or by 119 # switching the file to C++ and cleaning it up. 120 121 malloc_debug/ 122 # The code that implements the functionality to enable debugging of 123 # native allocation problems. 124 125 stdio/ 126 # These are legacy files of dubious provenance. We're working to clean 127 # this mess up, and this directory should disappear. 128 129 tools/ 130 # Various tools used to maintain bionic. 131 132 tzcode/ 133 # A modified superset of the IANA tzcode. Most of the modifications relate 134 # to Android's use of a single file (with corresponding index) to contain 135 # time zone data. 136 zoneinfo/ 137 # Android-format time zone data. 138 # See 'Updating tzdata' later. 139</pre> 140 141 142Adding system calls 143------------------- 144 145Adding a system call usually involves: 146 147 1. Add entries to SYSCALLS.TXT. 148 See SYSCALLS.TXT itself for documentation on the format. 149 2. Run the gensyscalls.py script. 150 3. Add constants (and perhaps types) to the appropriate header file. 151 Note that you should check to see whether the constants are already in 152 kernel uapi header files, in which case you just need to make sure that 153 the appropriate POSIX header file in libc/include/ includes the 154 relevant file or files. 155 4. Add function declarations to the appropriate header file. 156 5. Add at least basic tests. Even a test that deliberately supplies 157 an invalid argument helps check that we're generating the right symbol 158 and have the right declaration in the header file. (And strace(1) can 159 confirm that the correct system call is being made.) 160 161 162Updating kernel header files 163---------------------------- 164 165As mentioned above, this is currently a two-step process: 166 167 1. Use generate_uapi_headers.sh to go from a Linux source tree to appropriate 168 contents for external/kernel-headers/. 169 2. Run update_all.py to scrub those headers and import them into bionic. 170 171 172Updating tzdata 173--------------- 174 175This is fully automated (and these days handled by the libcore team, because 176they own icu, and that needs to be updated in sync with bionic): 177 178 1. Run update-tzdata.py in external/icu/tools/. 179 180 181Verifying changes 182----------------- 183 184If you make a change that is likely to have a wide effect on the tree (such as a 185libc header change), you should run `make checkbuild`. A regular `make` will 186_not_ build the entire tree; just the minimum number of projects that are 187required for the device. Tests, additional developer tools, and various other 188modules will not be built. Note that `make checkbuild` will not be complete 189either, as `make tests` covers a few additional modules, but generally speaking 190`make checkbuild` is enough. 191 192 193Running the tests 194----------------- 195 196The tests are all built from the tests/ directory. 197 198### Device tests 199 200 $ mma 201 $ adb remount 202 $ adb sync 203 $ adb shell /data/nativetest/bionic-unit-tests/bionic-unit-tests32 204 $ adb shell \ 205 /data/nativetest/bionic-unit-tests-static/bionic-unit-tests-static32 206 # Only for 64-bit targets 207 $ adb shell /data/nativetest64/bionic-unit-tests/bionic-unit-tests64 208 $ adb shell \ 209 /data/nativetest64/bionic-unit-tests-static/bionic-unit-tests-static64 210 211### Host tests 212 213The host tests require that you have `lunch`ed either an x86 or x86_64 target. 214 215 $ mma 216 $ mm bionic-unit-tests-run-on-host32 217 $ mm bionic-unit-tests-run-on-host64 # For 64-bit *targets* only. 218 219### Against glibc 220 221As a way to check that our tests do in fact test the correct behavior (and not 222just the behavior we think is correct), it is possible to run the tests against 223the host's glibc. The executables are already in your path. 224 225 $ mma 226 $ bionic-unit-tests-glibc32 227 $ bionic-unit-tests-glibc64 228 229 230Gathering test coverage 231----------------------- 232 233For either host or target coverage, you must first: 234 235 * `$ export NATIVE_COVERAGE=true` 236 * Note that the build system is ignorant to this flag being toggled, i.e. if 237 you change this flag, you will have to manually rebuild bionic. 238 * Set `bionic_coverage=true` in `libc/Android.mk` and `libm/Android.mk`. 239 240### Coverage from device tests 241 242 $ mma 243 $ adb sync 244 $ adb shell \ 245 GCOV_PREFIX=/data/local/tmp/gcov \ 246 GCOV_PREFIX_STRIP=`echo $ANDROID_BUILD_TOP | grep -o / | wc -l` \ 247 /data/nativetest/bionic-unit-tests/bionic-unit-tests32 248 $ acov 249 250`acov` will pull all coverage information from the device, push it to the right 251directories, run `lcov`, and open the coverage report in your browser. 252 253### Coverage from host tests 254 255First, build and run the host tests as usual (see above). 256 257 $ croot 258 $ lcov -c -d $ANDROID_PRODUCT_OUT -o coverage.info 259 $ genhtml -o covreport coverage.info # or lcov --list coverage.info 260 261The coverage report is now available at `covreport/index.html`. 262 263 264Attaching GDB to the tests 265-------------------------- 266 267Bionic's test runner will run each test in its own process by default to prevent 268tests failures from impacting other tests. This also has the added benefit of 269running them in parallel, so they are much faster. 270 271However, this also makes it difficult to run the tests under GDB. To prevent 272each test from being forked, run the tests with the flag `--no-isolate`. 273 274 27532-bit ABI bugs 276--------------- 277 278This probably belongs in the NDK documentation rather than here, but these 279are the known ABI bugs in the 32-bit ABI: 280 281 * `time_t` is 32-bit. <http://b/5819737>. In the 64-bit ABI, time_t is 282 64-bit. 283 284 * `off_t` is 32-bit. There is `off64_t`, and in newer releases there is 285 almost-complete support for `_FILE_OFFSET_BITS`. Unfortunately our stdio 286 implementation uses 32-bit offsets and -- worse -- function pointers to 287 functions that use 32-bit offsets, so there's no good way to implement 288 the last few pieces <http://b/24807045>. In the 64-bit ABI, off_t is 289 off64_t. 290 291 * `sigset_t` is too small on ARM and x86 (but correct on MIPS), so support 292 for real-time signals is broken. <http://b/5828899> In the 64-bit ABI, 293 `sigset_t` is the correct size for every architecture. 294