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Android.mk A D04-Dec-2017672

CPPLINT.cfg A D04-Dec-201775

CleanSpec.mk A D04-Dec-20172.4 KiB

README.md A D04-Dec-20179.3 KiB

README.md

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-dlmalloc/
100  upstream-freebsd/
101  upstream-netbsd/
102  upstream-openbsd/
103    # These directories contain unmolested upstream source. Any time we can
104    # just use a BSD implementation of something unmodified, we should.
105    # The structure under these directories mimics the upstream tree,
106    # but there's also...
107    android/
108      include/
109        # This is where we keep the hacks necessary to build BSD source
110        # in our world. The *-compat.h files are automatically included
111        # using -include, but we also provide equivalents for missing
112        # header/source files needed by the BSD implementation.
113
114  bionic/
115    # This is the biggest mess. The C++ files are files we own, typically
116    # because the Linux kernel interface is sufficiently different that we
117    # can't use any of the BSD implementations. The C files are usually
118    # legacy mess that needs to be sorted out, either by replacing it with
119    # current upstream source in one of the upstream directories or by
120    # switching the file to C++ and cleaning it up.
121
122  stdio/
123    # These are legacy files of dubious provenance. We're working to clean
124    # this mess up, and this directory should disappear.
125
126  tools/
127    # Various tools used to maintain bionic.
128
129  tzcode/
130    # A modified superset of the IANA tzcode. Most of the modifications relate
131    # to Android's use of a single file (with corresponding index) to contain
132    # time zone data.
133  zoneinfo/
134    # Android-format time zone data.
135    # See 'Updating tzdata' later.
136</pre>
137
138
139Adding system calls
140-------------------
141
142Adding a system call usually involves:
143
144  1. Add entries to SYSCALLS.TXT.
145     See SYSCALLS.TXT itself for documentation on the format.
146  2. Run the gensyscalls.py script.
147  3. Add constants (and perhaps types) to the appropriate header file.
148     Note that you should check to see whether the constants are already in
149     kernel uapi header files, in which case you just need to make sure that
150     the appropriate POSIX header file in libc/include/ includes the
151     relevant file or files.
152  4. Add function declarations to the appropriate header file.
153  5. Add at least basic tests. Even a test that deliberately supplies
154     an invalid argument helps check that we're generating the right symbol
155     and have the right declaration in the header file. (And strace(1) can
156     confirm that the correct system call is being made.)
157
158
159Updating kernel header files
160----------------------------
161
162As mentioned above, this is currently a two-step process:
163
164  1. Use generate_uapi_headers.sh to go from a Linux source tree to appropriate
165     contents for external/kernel-headers/.
166  2. Run update_all.py to scrub those headers and import them into bionic.
167
168
169Updating tzdata
170---------------
171
172This is fully automated:
173
174  1. Run update-tzdata.py.
175
176
177Verifying changes
178-----------------
179
180If you make a change that is likely to have a wide effect on the tree (such as a
181libc header change), you should run `make checkbuild`. A regular `make` will
182_not_ build the entire tree; just the minimum number of projects that are
183required for the device. Tests, additional developer tools, and various other
184modules will not be built. Note that `make checkbuild` will not be complete
185either, as `make tests` covers a few additional modules, but generally speaking
186`make checkbuild` is enough.
187
188
189Running the tests
190-----------------
191
192The tests are all built from the tests/ directory.
193
194### Device tests
195
196    $ mma
197    $ adb sync
198    $ adb shell /data/nativetest/bionic-unit-tests/bionic-unit-tests32
199    $ adb shell \
200        /data/nativetest/bionic-unit-tests-static/bionic-unit-tests-static32
201    # Only for 64-bit targets
202    $ adb shell /data/nativetest/bionic-unit-tests/bionic-unit-tests64
203    $ adb shell \
204        /data/nativetest/bionic-unit-tests-static/bionic-unit-tests-static64
205
206### Host tests
207
208The host tests require that you have `lunch`ed either an x86 or x86_64 target.
209
210    $ mma
211    $ mm bionic-unit-tests-run-on-host32
212    $ mm bionic-unit-tests-run-on-host64  # For 64-bit *targets* only.
213
214### Against glibc
215
216As a way to check that our tests do in fact test the correct behavior (and not
217just the behavior we think is correct), it is possible to run the tests against
218the host's glibc. The executables are already in your path.
219
220    $ mma
221    $ bionic-unit-tests-glibc32
222    $ bionic-unit-tests-glibc64
223
224
225Gathering test coverage
226-----------------------
227
228For either host or target coverage, you must first:
229
230 * `$ export NATIVE_COVERAGE=true`
231     * Note that the build system is ignorant to this flag being toggled, i.e. if
232       you change this flag, you will have to manually rebuild bionic.
233 * Set `bionic_coverage=true` in `libc/Android.mk` and `libm/Android.mk`.
234
235### Coverage from device tests
236
237    $ mma
238    $ adb sync
239    $ adb shell \
240        GCOV_PREFIX=/data/local/tmp/gcov \
241        GCOV_PREFIX_STRIP=`echo $ANDROID_BUILD_TOP | grep -o / | wc -l` \
242        /data/nativetest/bionic-unit-tests/bionic-unit-tests32
243    $ acov
244
245`acov` will pull all coverage information from the device, push it to the right
246directories, run `lcov`, and open the coverage report in your browser.
247
248### Coverage from host tests
249
250First, build and run the host tests as usual (see above).
251
252    $ croot
253    $ lcov -c -d $ANDROID_PRODUCT_OUT -o coverage.info
254    $ genhtml -o covreport coverage.info # or lcov --list coverage.info
255
256The coverage report is now available at `covreport/index.html`.
257
258
259LP32 ABI bugs
260-------------
261
262This probably belongs in the NDK documentation rather than here, but these
263are the known ABI bugs in LP32:
264
265 * `time_t` is 32-bit. <http://b/5819737>
266
267 * `off_t` is 32-bit. There is `off64_t`, but no `_FILE_OFFSET_BITS` support.
268   Many of the `off64_t` functions are missing in older releases, and
269   stdio uses 32-bit offsets, so there's no way to fully implement
270   `_FILE_OFFSET_BITS`.
271
272 * `sigset_t` is too small on ARM and x86 (but correct on MIPS), so support
273   for real-time signals is broken. <http://b/5828899>
274