• Home
  • History
  • Annotate
  • only in this directory
NameDateSize

..10-Sep-20194 KiB

.clang-formatH A D09-Sep-2019292

.gitignoreH A D09-Sep-201932

android-changes-for-ndk-developers.mdH A D09-Sep-201918.2 KiB

Android.bpH A D09-Sep-201916

Android.mkH A D09-Sep-201981

benchmarks/H09-Sep-20194 KiB

build/H09-Sep-20194 KiB

CleanSpec.mkH A D09-Sep-20192.6 KiB

CPPLINT.cfgH A D09-Sep-201975

docs/H09-Sep-20194 KiB

libc/H09-Sep-20194 KiB

libdl/H09-Sep-20194 KiB

libm/H09-Sep-20194 KiB

libstdc++/H09-Sep-20194 KiB

linker/H09-Sep-20194 KiB

OWNERSH A D09-Sep-2019222

PREUPLOAD.cfgH A D09-Sep-2019167

README.mdH A D09-Sep-201912.3 KiB

tests/H09-Sep-201912 KiB

tools/H09-Sep-20194 KiB

README.md

1Using bionic
2============
3
4See the [additional documentation](docs/).
5
6Working on bionic
7=================
8
9What are the big pieces of bionic?
10----------------------------------
11
12#### libc/ --- libc.so, libc.a
13
14The C library. Stuff like `fopen(3)` and `kill(2)`.
15
16#### libm/ --- libm.so, libm.a
17
18The math library. Traditionally Unix systems kept stuff like `sin(3)` and
19`cos(3)` in a separate library to save space in the days before shared
20libraries.
21
22#### libdl/ --- libdl.so
23
24The dynamic linker interface library. This is actually just a bunch of stubs
25that the dynamic linker replaces with pointers to its own implementation at
26runtime. This is where stuff like `dlopen(3)` lives.
27
28#### libstdc++/ --- libstdc++.so
29
30The C++ ABI support functions. The C++ compiler doesn't know how to implement
31thread-safe static initialization and the like, so it just calls functions that
32are supplied by the system. Stuff like `__cxa_guard_acquire` and
33`__cxa_pure_virtual` live here.
34
35#### linker/ --- /system/bin/linker and /system/bin/linker64
36
37The dynamic linker. When you run a dynamically-linked executable, its ELF file
38has a `DT_INTERP` entry that says "use the following program to start me".  On
39Android, that's either `linker` or `linker64` (depending on whether it's a
4032-bit or 64-bit executable). It's responsible for loading the ELF executable
41into memory and resolving references to symbols (so that when your code tries to
42jump to `fopen(3)`, say, it lands in the right place).
43
44#### tests/ --- unit tests
45
46The `tests/` directory contains unit tests. Roughly arranged as one file per
47publicly-exported header file.
48
49#### benchmarks/ --- benchmarks
50
51The `benchmarks/` directory contains benchmarks, with its own [documentation](benchmarks/README.md).
52
53
54What's in libc/?
55----------------
56
57<pre>
58libc/
59  arch-arm/
60  arch-arm64/
61  arch-common/
62  arch-mips/
63  arch-mips64/
64  arch-x86/
65  arch-x86_64/
66    # Each architecture has its own subdirectory for stuff that isn't shared
67    # because it's architecture-specific. There will be a .mk file in here that
68    # drags in all the architecture-specific files.
69    bionic/
70      # Every architecture needs a handful of machine-specific assembler files.
71      # They live here.
72    include/
73      machine/
74        # The majority of header files are actually in libc/include/, but many
75        # of them pull in a <machine/something.h> for things like limits,
76        # endianness, and how floating point numbers are represented. Those
77        # headers live here.
78    string/
79      # Most architectures have a handful of optional assembler files
80      # implementing optimized versions of various routines. The <string.h>
81      # functions are particular favorites.
82    syscalls/
83      # The syscalls directories contain script-generated assembler files.
84      # See 'Adding system calls' later.
85
86  include/
87    # The public header files on everyone's include path. These are a mixture of
88    # files written by us and files taken from BSD.
89
90  kernel/
91    # The kernel uapi header files. These are scrubbed copies of the originals
92    # in external/kernel-headers/. These files must not be edited directly. The
93    # generate_uapi_headers.sh script should be used to go from a kernel tree to
94    # external/kernel-headers/ --- this takes care of the architecture-specific
95    # details. The update_all.py script should be used to regenerate bionic's
96    # scrubbed headers from external/kernel-headers/.
97
98  private/
99    # These are private header files meant for use within bionic itself.
100
101  dns/
102    # Contains the DNS resolver (originates from NetBSD code).
103
104  upstream-freebsd/
105  upstream-netbsd/
106  upstream-openbsd/
107    # These directories contain unmolested upstream source. Any time we can
108    # just use a BSD implementation of something unmodified, we should.
109    # The structure under these directories mimics the upstream tree,
110    # but there's also...
111    android/
112      include/
113        # This is where we keep the hacks necessary to build BSD source
114        # in our world. The *-compat.h files are automatically included
115        # using -include, but we also provide equivalents for missing
116        # header/source files needed by the BSD implementation.
117
118  bionic/
119    # This is the biggest mess. The C++ files are files we own, typically
120    # because the Linux kernel interface is sufficiently different that we
121    # can't use any of the BSD implementations. The C files are usually
122    # legacy mess that needs to be sorted out, either by replacing it with
123    # current upstream source in one of the upstream directories or by
124    # switching the file to C++ and cleaning it up.
125
126  malloc_debug/
127    # The code that implements the functionality to enable debugging of
128    # native allocation problems.
129
130  stdio/
131    # These are legacy files of dubious provenance. We're working to clean
132    # this mess up, and this directory should disappear.
133
134  tools/
135    # Various tools used to maintain bionic.
136
137  tzcode/
138    # A modified superset of the IANA tzcode. Most of the modifications relate
139    # to Android's use of a single file (with corresponding index) to contain
140    # time zone data.
141  zoneinfo/
142    # Android-format time zone data.
143    # See 'Updating tzdata' later.
144</pre>
145
146
147Adding libc wrappers for system calls
148-------------------------------------
149
150The first question you should ask is "should I add a libc wrapper for
151this system call?". The answer is usually "no".
152
153The answer is "yes" if the system call is part of the POSIX standard.
154
155The answer is probably "yes" if the system call has a wrapper in at
156least one other C library.
157
158The answer may be "yes" if the system call has three/four distinct
159users in different projects, and there isn't a more specific library
160that would make more sense as the place to add the wrapper.
161
162In all other cases, you should use
163[syscall(3)](http://man7.org/linux/man-pages/man2/syscall.2.html) instead.
164
165Adding a system call usually involves:
166
167  1. Add entries to SYSCALLS.TXT.
168     See SYSCALLS.TXT itself for documentation on the format.
169  2. Run the gensyscalls.py script.
170  3. Add constants (and perhaps types) to the appropriate header file.
171     Note that you should check to see whether the constants are already in
172     kernel uapi header files, in which case you just need to make sure that
173     the appropriate POSIX header file in libc/include/ includes the
174     relevant file or files.
175  4. Add function declarations to the appropriate header file. Don't forget
176     to include the appropriate `__INTRODUCED_IN()`.
177  5. Add the function name to the correct section in libc/libc.map.txt and
178     run `./libc/tools/genversion-scripts.py`.
179  6. Add at least basic tests. Even a test that deliberately supplies
180     an invalid argument helps check that we're generating the right symbol
181     and have the right declaration in the header file, and that you correctly
182     updated the maps in step 5. (You can use strace(1) to confirm that the
183     correct system call is being made.)
184
185
186Updating kernel header files
187----------------------------
188
189As mentioned above, this is currently a two-step process:
190
191  1. Use generate_uapi_headers.sh to go from a Linux source tree to appropriate
192     contents for external/kernel-headers/.
193  2. Run update_all.py to scrub those headers and import them into bionic.
194
195Note that if you're actually just trying to expose device-specific headers to
196build your device drivers, you shouldn't modify bionic. Instead use
197`TARGET_DEVICE_KERNEL_HEADERS` and friends described in [config.mk](https://android.googlesource.com/platform/build/+/master/core/config.mk#186).
198
199
200Updating tzdata
201---------------
202
203This is fully automated (and these days handled by the libcore team, because
204they own icu, and that needs to be updated in sync with bionic):
205
206  1. Run update-tzdata.py in external/icu/tools/.
207
208
209Verifying changes
210-----------------
211
212If you make a change that is likely to have a wide effect on the tree (such as a
213libc header change), you should run `make checkbuild`. A regular `make` will
214_not_ build the entire tree; just the minimum number of projects that are
215required for the device. Tests, additional developer tools, and various other
216modules will not be built. Note that `make checkbuild` will not be complete
217either, as `make tests` covers a few additional modules, but generally speaking
218`make checkbuild` is enough.
219
220
221Running the tests
222-----------------
223
224The tests are all built from the tests/ directory.
225
226### Device tests
227
228    $ mma # In $ANDROID_ROOT/bionic.
229    $ adb root && adb remount && adb sync
230    $ adb shell /data/nativetest/bionic-unit-tests/bionic-unit-tests
231    $ adb shell \
232        /data/nativetest/bionic-unit-tests-static/bionic-unit-tests-static
233    # Only for 64-bit targets
234    $ adb shell /data/nativetest64/bionic-unit-tests/bionic-unit-tests
235    $ adb shell \
236        /data/nativetest64/bionic-unit-tests-static/bionic-unit-tests-static
237
238Note that we use our own custom gtest runner that offers a superset of the
239options documented at
240<https://github.com/google/googletest/blob/master/googletest/docs/AdvancedGuide.md#running-test-programs-advanced-options>,
241in particular for test isolation and parallelism (both on by default).
242
243### Device tests via CTS
244
245Most of the unit tests are executed by CTS. By default, CTS runs as
246a non-root user, so the unit tests must also pass when not run as root.
247Some tests cannot do any useful work unless run as root. In this case,
248the test should check `getuid() == 0` and do nothing otherwise (typically
249we log in this case to prevent accidents!). Obviously, if the test can be
250rewritten to not require root, that's an even better solution.
251
252Currently, the list of bionic CTS tests is generated at build time by
253running a host version of the test executable and dumping the list of
254all tests. In order for this to continue to work, all architectures must
255have the same number of tests, and the host version of the executable
256must also have the same number of tests.
257
258Running the gtests directly is orders of magnitude faster than using CTS,
259but in cases where you really have to run CTS:
260
261    $ make cts # In $ANDROID_ROOT.
262    $ adb unroot # Because real CTS doesn't run as root.
263    # This will sync any *test* changes, but not *code* changes:
264    $ cts-tradefed \
265        run singleCommand cts --skip-preconditions -m CtsBionicTestCases
266
267### Host tests
268
269The host tests require that you have `lunch`ed either an x86 or x86_64 target.
270Note that due to ABI limitations (specifically, the size of pthread_mutex_t),
27132-bit bionic requires PIDs less than 65536. To enforce this, set /proc/sys/kernel/pid_max
272to 65536.
273
274    $ ./tests/run-on-host.sh 32
275    $ ./tests/run-on-host.sh 64   # For x86_64-bit *targets* only.
276
277You can supply gtest flags as extra arguments to this script.
278
279### Against glibc
280
281As a way to check that our tests do in fact test the correct behavior (and not
282just the behavior we think is correct), it is possible to run the tests against
283the host's glibc.
284
285    $ ./tests/run-on-host.sh glibc
286
287
288Gathering test coverage
289-----------------------
290
291For either host or target coverage, you must first:
292
293 * `$ export NATIVE_COVERAGE=true`
294     * Note that the build system is ignorant to this flag being toggled, i.e. if
295       you change this flag, you will have to manually rebuild bionic.
296 * Set `bionic_coverage=true` in `libc/Android.mk` and `libm/Android.mk`.
297
298### Coverage from device tests
299
300    $ mma
301    $ adb sync
302    $ adb shell \
303        GCOV_PREFIX=/data/local/tmp/gcov \
304        GCOV_PREFIX_STRIP=`echo $ANDROID_BUILD_TOP | grep -o / | wc -l` \
305        /data/nativetest/bionic-unit-tests/bionic-unit-tests
306    $ acov
307
308`acov` will pull all coverage information from the device, push it to the right
309directories, run `lcov`, and open the coverage report in your browser.
310
311### Coverage from host tests
312
313First, build and run the host tests as usual (see above).
314
315    $ croot
316    $ lcov -c -d $ANDROID_PRODUCT_OUT -o coverage.info
317    $ genhtml -o covreport coverage.info # or lcov --list coverage.info
318
319The coverage report is now available at `covreport/index.html`.
320
321
322Attaching GDB to the tests
323--------------------------
324
325Bionic's test runner will run each test in its own process by default to prevent
326tests failures from impacting other tests. This also has the added benefit of
327running them in parallel, so they are much faster.
328
329However, this also makes it difficult to run the tests under GDB. To prevent
330each test from being forked, run the tests with the flag `--no-isolate`.
331
332
33332-bit ABI bugs
334---------------
335
336See [32-bit ABI bugs](docs/32-bit-abi.md).
337