4 What are the big pieces of bionic?
5 ----------------------------------
7 #### libc/ --- libc.so, libc.a
9 The C library. Stuff like `fopen(3)` and `kill(2)`.
11 #### libm/ --- libm.so, libm.a
13 The 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
17 #### libdl/ --- libdl.so
19 The dynamic linker interface library. This is actually just a bunch of stubs
20 that the dynamic linker replaces with pointers to its own implementation at
21 runtime. This is where stuff like `dlopen(3)` lives.
23 #### libstdc++/ --- libstdc++.so
25 The C++ ABI support functions. The C++ compiler doesn't know how to implement
26 thread-safe static initialization and the like, so it just calls functions that
27 are supplied by the system. Stuff like `__cxa_guard_acquire` and
28 `__cxa_pure_virtual` live here.
30 #### linker/ --- /system/bin/linker and /system/bin/linker64
32 The dynamic linker. When you run a dynamically-linked executable, its ELF file
33 has a `DT_INTERP` entry that says "use the following program to start me". On
34 Android, that's either `linker` or `linker64` (depending on whether it's a
35 32-bit or 64-bit executable). It's responsible for loading the ELF executable
36 into memory and resolving references to symbols (so that when your code tries to
37 jump to `fopen(3)`, say, it lands in the right place).
39 #### tests/ --- unit tests
41 The `tests/` directory contains unit tests. Roughly arranged as one file per
42 publicly-exported header file.
44 #### benchmarks/ --- benchmarks
46 The `benchmarks/` directory contains benchmarks.
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.
65 # Every architecture needs a handful of machine-specific assembler files.
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
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.
78 # The syscalls directories contain script-generated assembler files.
79 # See 'Adding system calls' later.
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.
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/.
94 # These are private header files meant for use within bionic itself.
97 # Contains the DNS resolver (originates from NetBSD code).
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...
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.
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.
122 # The code that implements the functionality to enable debugging of
123 # native allocation problems.
126 # These are legacy files of dubious provenance. We're working to clean
127 # this mess up, and this directory should disappear.
130 # Various tools used to maintain bionic.
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
137 # Android-format time zone data.
138 # See 'Updating tzdata' later.
145 Adding a system call usually involves:
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 the function name to the correct section in libc/libc.map.txt and
157 run `./libc/tools/genversion-scripts.py`.
158 6. Add at least basic tests. Even a test that deliberately supplies
159 an invalid argument helps check that we're generating the right symbol
160 and have the right declaration in the header file, and that you correctly
161 updated the maps in step 5. (You can use strace(1) to confirm that the
162 correct system call is being made.)
165 Updating kernel header files
166 ----------------------------
168 As mentioned above, this is currently a two-step process:
170 1. Use generate_uapi_headers.sh to go from a Linux source tree to appropriate
171 contents for external/kernel-headers/.
172 2. Run update_all.py to scrub those headers and import them into bionic.
178 This is fully automated (and these days handled by the libcore team, because
179 they own icu, and that needs to be updated in sync with bionic):
181 1. Run update-tzdata.py in external/icu/tools/.
187 If you make a change that is likely to have a wide effect on the tree (such as a
188 libc header change), you should run `make checkbuild`. A regular `make` will
189 _not_ build the entire tree; just the minimum number of projects that are
190 required for the device. Tests, additional developer tools, and various other
191 modules will not be built. Note that `make checkbuild` will not be complete
192 either, as `make tests` covers a few additional modules, but generally speaking
193 `make checkbuild` is enough.
199 The tests are all built from the tests/ directory.
203 $ mma # In $ANDROID_ROOT/bionic.
204 $ adb root && adb remount && adb sync
205 $ adb shell /data/nativetest/bionic-unit-tests/bionic-unit-tests32
207 /data/nativetest/bionic-unit-tests-static/bionic-unit-tests-static32
208 # Only for 64-bit targets
209 $ adb shell /data/nativetest64/bionic-unit-tests/bionic-unit-tests64
211 /data/nativetest64/bionic-unit-tests-static/bionic-unit-tests-static64
213 Note that we use our own custom gtest runner that offers a superset of the
214 options documented at
215 <https://github.com/google/googletest/blob/master/googletest/docs/AdvancedGuide.md#running-test-programs-advanced-options>,
216 in particular for test isolation and parallelism (both on by default).
218 ### Device tests via CTS
220 Most of the unit tests are executed by CTS. By default, CTS runs as
221 a non-root user, so the unit tests must also pass when not run as root.
222 Some tests cannot do any useful work unless run as root. In this case,
223 the test should check `getuid() == 0` and do nothing otherwise (typically
224 we log in this case to prevent accidents!). Obviously, if the test can be
225 rewritten to not require root, that's an even better solution.
227 Currently, the list of bionic CTS tests is generated at build time by
228 running a host version of the test executable and dumping the list of
229 all tests. In order for this to continue to work, all architectures must
230 have the same number of tests, and the host version of the executable
231 must also have the same number of tests.
233 Running the gtests directly is orders of magnitude faster than using CTS,
234 but in cases where you really have to run CTS:
236 $ make cts # In $ANDROID_ROOT.
237 $ adb unroot # Because real CTS doesn't run as root.
238 # This will sync any *test* changes, but not *code* changes:
240 run singleCommand cts --skip-preconditions -m CtsBionicTestCases
244 The host tests require that you have `lunch`ed either an x86 or x86_64 target.
245 Note that due to ABI limitations (specifically, the size of pthread_mutex_t),
246 32-bit bionic requires PIDs less than 65536. To enforce this, set /proc/sys/kernel/pid_max
249 $ ./tests/run-on-host.sh 32
250 $ ./tests/run-on-host.sh 64 # For x86_64-bit *targets* only.
252 You can supply gtest flags as extra arguments to this script.
256 As a way to check that our tests do in fact test the correct behavior (and not
257 just the behavior we think is correct), it is possible to run the tests against
260 $ ./tests/run-on-host.sh glibc
263 Gathering test coverage
264 -----------------------
266 For either host or target coverage, you must first:
268 * `$ export NATIVE_COVERAGE=true`
269 * Note that the build system is ignorant to this flag being toggled, i.e. if
270 you change this flag, you will have to manually rebuild bionic.
271 * Set `bionic_coverage=true` in `libc/Android.mk` and `libm/Android.mk`.
273 ### Coverage from device tests
278 GCOV_PREFIX=/data/local/tmp/gcov \
279 GCOV_PREFIX_STRIP=`echo $ANDROID_BUILD_TOP | grep -o / | wc -l` \
280 /data/nativetest/bionic-unit-tests/bionic-unit-tests32
283 `acov` will pull all coverage information from the device, push it to the right
284 directories, run `lcov`, and open the coverage report in your browser.
286 ### Coverage from host tests
288 First, build and run the host tests as usual (see above).
291 $ lcov -c -d $ANDROID_PRODUCT_OUT -o coverage.info
292 $ genhtml -o covreport coverage.info # or lcov --list coverage.info
294 The coverage report is now available at `covreport/index.html`.
297 Running the benchmarks
298 ----------------------
300 ### Device benchmarks
305 $ adb shell /data/nativetest/bionic-benchmarks/bionic-benchmarks
306 $ adb shell /data/nativetest64/bionic-benchmarks/bionic-benchmarks
308 You can use `--benchmark_filter=getpid` to just run benchmarks with "getpid"
313 See the "Host tests" section of "Running the tests" above.
316 Attaching GDB to the tests
317 --------------------------
319 Bionic's test runner will run each test in its own process by default to prevent
320 tests failures from impacting other tests. This also has the added benefit of
321 running them in parallel, so they are much faster.
323 However, this also makes it difficult to run the tests under GDB. To prevent
324 each test from being forked, run the tests with the flag `--no-isolate`.
330 This probably belongs in the NDK documentation rather than here, but these
331 are the known ABI bugs in the 32-bit ABI:
333 * `time_t` is 32-bit. <http://b/5819737>. In the 64-bit ABI, time_t is
336 * `off_t` is 32-bit. There is `off64_t`, and in newer releases there is
337 almost-complete support for `_FILE_OFFSET_BITS`. Unfortunately our stdio
338 implementation uses 32-bit offsets and -- worse -- function pointers to
339 functions that use 32-bit offsets, so there's no good way to implement
340 the last few pieces <http://b/24807045>. In the 64-bit ABI, off_t is
343 * `sigset_t` is too small on ARM and x86 (but correct on MIPS), so support
344 for real-time signals is broken. <http://b/5828899> In the 64-bit ABI,
345 `sigset_t` is the correct size for every architecture.