285 lines
9.7 KiB
Markdown
285 lines
9.7 KiB
Markdown
Working on bionic
|
|
=================
|
|
|
|
What are the big pieces of bionic?
|
|
----------------------------------
|
|
|
|
#### libc/ --- libc.so, libc.a
|
|
|
|
The C library. Stuff like `fopen(3)` and `kill(2)`.
|
|
|
|
#### libm/ --- libm.so, libm.a
|
|
|
|
The math library. Traditionally Unix systems kept stuff like `sin(3)` and
|
|
`cos(3)` in a separate library to save space in the days before shared
|
|
libraries.
|
|
|
|
#### libdl/ --- libdl.so
|
|
|
|
The dynamic linker interface library. This is actually just a bunch of stubs
|
|
that the dynamic linker replaces with pointers to its own implementation at
|
|
runtime. This is where stuff like `dlopen(3)` lives.
|
|
|
|
#### libstdc++/ --- libstdc++.so
|
|
|
|
The C++ ABI support functions. The C++ compiler doesn't know how to implement
|
|
thread-safe static initialization and the like, so it just calls functions that
|
|
are supplied by the system. Stuff like `__cxa_guard_acquire` and
|
|
`__cxa_pure_virtual` live here.
|
|
|
|
#### linker/ --- /system/bin/linker and /system/bin/linker64
|
|
|
|
The dynamic linker. When you run a dynamically-linked executable, its ELF file
|
|
has a `DT_INTERP` entry that says "use the following program to start me". On
|
|
Android, that's either `linker` or `linker64` (depending on whether it's a
|
|
32-bit or 64-bit executable). It's responsible for loading the ELF executable
|
|
into memory and resolving references to symbols (so that when your code tries to
|
|
jump to `fopen(3)`, say, it lands in the right place).
|
|
|
|
#### tests/ --- unit tests
|
|
|
|
The `tests/` directory contains unit tests. Roughly arranged as one file per
|
|
publicly-exported header file.
|
|
|
|
#### benchmarks/ --- benchmarks
|
|
|
|
The `benchmarks/` directory contains benchmarks.
|
|
|
|
|
|
What's in libc/?
|
|
----------------
|
|
|
|
<pre>
|
|
libc/
|
|
arch-arm/
|
|
arch-arm64/
|
|
arch-common/
|
|
arch-mips/
|
|
arch-mips64/
|
|
arch-x86/
|
|
arch-x86_64/
|
|
# Each architecture has its own subdirectory for stuff that isn't shared
|
|
# because it's architecture-specific. There will be a .mk file in here that
|
|
# drags in all the architecture-specific files.
|
|
bionic/
|
|
# Every architecture needs a handful of machine-specific assembler files.
|
|
# They live here.
|
|
include/
|
|
machine/
|
|
# The majority of header files are actually in libc/include/, but many
|
|
# of them pull in a <machine/something.h> for things like limits,
|
|
# endianness, and how floating point numbers are represented. Those
|
|
# headers live here.
|
|
string/
|
|
# Most architectures have a handful of optional assembler files
|
|
# implementing optimized versions of various routines. The <string.h>
|
|
# functions are particular favorites.
|
|
syscalls/
|
|
# The syscalls directories contain script-generated assembler files.
|
|
# See 'Adding system calls' later.
|
|
|
|
include/
|
|
# The public header files on everyone's include path. These are a mixture of
|
|
# files written by us and files taken from BSD.
|
|
|
|
kernel/
|
|
# The kernel uapi header files. These are scrubbed copies of the originals
|
|
# in external/kernel-headers/. These files must not be edited directly. The
|
|
# generate_uapi_headers.sh script should be used to go from a kernel tree to
|
|
# external/kernel-headers/ --- this takes care of the architecture-specific
|
|
# details. The update_all.py script should be used to regenerate bionic's
|
|
# scrubbed headers from external/kernel-headers/.
|
|
|
|
private/
|
|
# These are private header files meant for use within bionic itself.
|
|
|
|
dns/
|
|
# Contains the DNS resolver (originates from NetBSD code).
|
|
|
|
upstream-dlmalloc/
|
|
upstream-freebsd/
|
|
upstream-netbsd/
|
|
upstream-openbsd/
|
|
# These directories contain unmolested upstream source. Any time we can
|
|
# just use a BSD implementation of something unmodified, we should.
|
|
# The structure under these directories mimics the upstream tree,
|
|
# but there's also...
|
|
android/
|
|
include/
|
|
# This is where we keep the hacks necessary to build BSD source
|
|
# in our world. The *-compat.h files are automatically included
|
|
# using -include, but we also provide equivalents for missing
|
|
# header/source files needed by the BSD implementation.
|
|
|
|
bionic/
|
|
# This is the biggest mess. The C++ files are files we own, typically
|
|
# because the Linux kernel interface is sufficiently different that we
|
|
# can't use any of the BSD implementations. The C files are usually
|
|
# legacy mess that needs to be sorted out, either by replacing it with
|
|
# current upstream source in one of the upstream directories or by
|
|
# switching the file to C++ and cleaning it up.
|
|
|
|
stdio/
|
|
# These are legacy files of dubious provenance. We're working to clean
|
|
# this mess up, and this directory should disappear.
|
|
|
|
tools/
|
|
# Various tools used to maintain bionic.
|
|
|
|
tzcode/
|
|
# A modified superset of the IANA tzcode. Most of the modifications relate
|
|
# to Android's use of a single file (with corresponding index) to contain
|
|
# time zone data.
|
|
zoneinfo/
|
|
# Android-format time zone data.
|
|
# See 'Updating tzdata' later.
|
|
</pre>
|
|
|
|
|
|
Adding system calls
|
|
-------------------
|
|
|
|
Adding a system call usually involves:
|
|
|
|
1. Add entries to SYSCALLS.TXT.
|
|
See SYSCALLS.TXT itself for documentation on the format.
|
|
2. Run the gensyscalls.py script.
|
|
3. Add constants (and perhaps types) to the appropriate header file.
|
|
Note that you should check to see whether the constants are already in
|
|
kernel uapi header files, in which case you just need to make sure that
|
|
the appropriate POSIX header file in libc/include/ includes the
|
|
relevant file or files.
|
|
4. Add function declarations to the appropriate header file.
|
|
5. Add at least basic tests. Even a test that deliberately supplies
|
|
an invalid argument helps check that we're generating the right symbol
|
|
and have the right declaration in the header file. (And strace(1) can
|
|
confirm that the correct system call is being made.)
|
|
|
|
|
|
Updating kernel header files
|
|
----------------------------
|
|
|
|
As mentioned above, this is currently a two-step process:
|
|
|
|
1. Use generate_uapi_headers.sh to go from a Linux source tree to appropriate
|
|
contents for external/kernel-headers/.
|
|
2. Run update_all.py to scrub those headers and import them into bionic.
|
|
|
|
|
|
Updating tzdata
|
|
---------------
|
|
|
|
This is fully automated:
|
|
|
|
1. Run update-tzdata.py.
|
|
|
|
|
|
Verifying changes
|
|
-----------------
|
|
|
|
If you make a change that is likely to have a wide effect on the tree (such as a
|
|
libc header change), you should run `make checkbuild`. A regular `make` will
|
|
_not_ build the entire tree; just the minimum number of projects that are
|
|
required for the device. Tests, additional developer tools, and various other
|
|
modules will not be built. Note that `make checkbuild` will not be complete
|
|
either, as `make tests` covers a few additional modules, but generally speaking
|
|
`make checkbuild` is enough.
|
|
|
|
|
|
Running the tests
|
|
-----------------
|
|
|
|
The tests are all built from the tests/ directory.
|
|
|
|
### Device tests
|
|
|
|
$ mma
|
|
$ adb remount
|
|
$ adb sync
|
|
$ adb shell /data/nativetest/bionic-unit-tests/bionic-unit-tests32
|
|
$ adb shell \
|
|
/data/nativetest/bionic-unit-tests-static/bionic-unit-tests-static32
|
|
# Only for 64-bit targets
|
|
$ adb shell /data/nativetest64/bionic-unit-tests/bionic-unit-tests64
|
|
$ adb shell \
|
|
/data/nativetest64/bionic-unit-tests-static/bionic-unit-tests-static64
|
|
|
|
### Host tests
|
|
|
|
The host tests require that you have `lunch`ed either an x86 or x86_64 target.
|
|
|
|
$ mma
|
|
$ mm bionic-unit-tests-run-on-host32
|
|
$ mm bionic-unit-tests-run-on-host64 # For 64-bit *targets* only.
|
|
|
|
### Against glibc
|
|
|
|
As a way to check that our tests do in fact test the correct behavior (and not
|
|
just the behavior we think is correct), it is possible to run the tests against
|
|
the host's glibc. The executables are already in your path.
|
|
|
|
$ mma
|
|
$ bionic-unit-tests-glibc32
|
|
$ bionic-unit-tests-glibc64
|
|
|
|
|
|
Gathering test coverage
|
|
-----------------------
|
|
|
|
For either host or target coverage, you must first:
|
|
|
|
* `$ export NATIVE_COVERAGE=true`
|
|
* Note that the build system is ignorant to this flag being toggled, i.e. if
|
|
you change this flag, you will have to manually rebuild bionic.
|
|
* Set `bionic_coverage=true` in `libc/Android.mk` and `libm/Android.mk`.
|
|
|
|
### Coverage from device tests
|
|
|
|
$ mma
|
|
$ adb sync
|
|
$ adb shell \
|
|
GCOV_PREFIX=/data/local/tmp/gcov \
|
|
GCOV_PREFIX_STRIP=`echo $ANDROID_BUILD_TOP | grep -o / | wc -l` \
|
|
/data/nativetest/bionic-unit-tests/bionic-unit-tests32
|
|
$ acov
|
|
|
|
`acov` will pull all coverage information from the device, push it to the right
|
|
directories, run `lcov`, and open the coverage report in your browser.
|
|
|
|
### Coverage from host tests
|
|
|
|
First, build and run the host tests as usual (see above).
|
|
|
|
$ croot
|
|
$ lcov -c -d $ANDROID_PRODUCT_OUT -o coverage.info
|
|
$ genhtml -o covreport coverage.info # or lcov --list coverage.info
|
|
|
|
The coverage report is now available at `covreport/index.html`.
|
|
|
|
|
|
Attaching GDB to the tests
|
|
--------------------------
|
|
|
|
Bionic's test runner will run each test in its own process by default to prevent
|
|
tests failures from impacting other tests. This also has the added benefit of
|
|
running them in parallel, so they are much faster.
|
|
|
|
However, this also makes it difficult to run the tests under GDB. To prevent
|
|
each test from being forked, run the tests with the flag `--no-isolate`.
|
|
|
|
|
|
LP32 ABI bugs
|
|
-------------
|
|
|
|
This probably belongs in the NDK documentation rather than here, but these
|
|
are the known ABI bugs in LP32:
|
|
|
|
* `time_t` is 32-bit. <http://b/5819737>
|
|
|
|
* `off_t` is 32-bit. There is `off64_t`, but no `_FILE_OFFSET_BITS` support.
|
|
Many of the `off64_t` functions are missing in older releases, and
|
|
stdio uses 32-bit offsets, so there's no way to fully implement
|
|
`_FILE_OFFSET_BITS`.
|
|
|
|
* `sigset_t` is too small on ARM and x86 (but correct on MIPS), so support
|
|
for real-time signals is broken. <http://b/5828899>
|