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).
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...
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.
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.
123 # These are legacy files of dubious provenance. We're working to clean
124 # this mess up, and this directory should disappear.
127 # Various tools used to maintain bionic.
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
134 # Android-format time zone data.
135 # See 'Updating tzdata' later.
142 Adding a system call usually involves:
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.)
159 Updating kernel header files
160 ----------------------------
162 As mentioned above, this is currently a two-step process:
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.
172 This is fully automated:
174 1. Run update-tzdata.py.
180 If you make a change that is likely to have a wide effect on the tree (such as a
181 libc 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
183 required for the device. Tests, additional developer tools, and various other
184 modules will not be built. Note that `make checkbuild` will not be complete
185 either, as `make tests` covers a few additional modules, but generally speaking
186 `make checkbuild` is enough.
192 The tests are all built from the tests/ directory.
198 $ adb shell /data/nativetest/bionic-unit-tests/bionic-unit-tests32
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
204 /data/nativetest/bionic-unit-tests-static/bionic-unit-tests-static64
208 The host tests require that you have `lunch`ed either an x86 or x86_64 target.
211 $ mm bionic-unit-tests-run-on-host32
212 $ mm bionic-unit-tests-run-on-host64 # For 64-bit *targets* only.
216 As a way to check that our tests do in fact test the correct behavior (and not
217 just the behavior we think is correct), it is possible to run the tests against
218 the host's glibc. The executables are already in your path.
221 $ bionic-unit-tests-glibc32
222 $ bionic-unit-tests-glibc64
225 Gathering test coverage
226 -----------------------
228 For either host or target coverage, you must first:
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`.
235 ### Coverage from device tests
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
245 `acov` will pull all coverage information from the device, push it to the right
246 directories, run `lcov`, and open the coverage report in your browser.
248 ### Coverage from host tests
250 First, build and run the host tests as usual (see above).
253 $ lcov -c -d $ANDROID_PRODUCT_OUT -o coverage.info
254 $ genhtml -o covreport coverage.info # or lcov --list coverage.info
256 The coverage report is now available at `covreport/index.html`.
262 This probably belongs in the NDK documentation rather than here, but these
263 are the known ABI bugs in LP32:
265 * `time_t` is 32-bit. <http://b/5819737>
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
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>