Explain up-front what bionic actually _is_.
Also fix formatting of "What's in libc/?" section, and remove obsolete include/machine. Also unify # vs --- syntax. Bug: N/A Test: N/A Change-Id: I6a7a2828e700d5e03c7209f55691278326230bd1
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Elliott Hughes
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README.md
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README.md
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Using bionic
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============
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# bionic
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See the [additional documentation](docs/).
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[bionic](https://en.wikipedia.org/wiki/Bionic_(software)) is Android's
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C library, math library, and dynamic linker.
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Working on bionic
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=================
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# Using bionic as an app developer
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What are the big pieces of bionic?
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----------------------------------
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See the [user documentation](docs/).
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# Working on bionic itself
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This documentation is about making changes to bionic itself.
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## What are the big pieces of bionic?
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#### libc/ --- libc.so, libc.a
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@ -51,10 +55,9 @@ publicly-exported header file.
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The `benchmarks/` directory contains benchmarks, with its own [documentation](benchmarks/README.md).
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What's in libc/?
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----------------
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## What's in libc/?
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<pre>
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```
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libc/
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arch-arm/
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arch-arm64/
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@ -69,12 +72,6 @@ libc/
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bionic/
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# Every architecture needs a handful of machine-specific assembler files.
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# They live here.
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include/
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machine/
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# The majority of header files are actually in libc/include/, but many
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# of them pull in a <machine/something.h> for things like limits,
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# endianness, and how floating point numbers are represented. Those
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# headers live here.
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string/
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# Most architectures have a handful of optional assembler files
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# implementing optimized versions of various routines. The <string.h>
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@ -141,11 +138,10 @@ libc/
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zoneinfo/
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# Android-format time zone data.
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# See 'Updating tzdata' later.
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</pre>
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```
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Adding libc wrappers for system calls
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-------------------------------------
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## Adding libc wrappers for system calls
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The first question you should ask is "should I add a libc wrapper for
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this system call?". The answer is usually "no".
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@ -183,8 +179,7 @@ Adding a system call usually involves:
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correct system call is being made.)
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Updating kernel header files
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----------------------------
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## Updating kernel header files
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As mentioned above, this is currently a two-step process:
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@ -197,8 +192,7 @@ build your device drivers, you shouldn't modify bionic. Instead use
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`TARGET_DEVICE_KERNEL_HEADERS` and friends described in [config.mk](https://android.googlesource.com/platform/build/+/master/core/config.mk#186).
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Updating tzdata
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---------------
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## Updating tzdata
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This is fully automated (and these days handled by the libcore team, because
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they own icu, and that needs to be updated in sync with bionic):
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@ -206,8 +200,7 @@ they own icu, and that needs to be updated in sync with bionic):
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1. Run update-tzdata.py in external/icu/tools/.
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Verifying changes
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-----------------
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## Verifying changes
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If you make a change that is likely to have a wide effect on the tree (such as a
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libc header change), you should run `make checkbuild`. A regular `make` will
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@ -218,8 +211,7 @@ either, as `make tests` covers a few additional modules, but generally speaking
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`make checkbuild` is enough.
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Running the tests
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-----------------
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## Running the tests
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The tests are all built from the tests/ directory.
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@ -285,8 +277,7 @@ the host's glibc.
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$ ./tests/run-on-host.sh glibc
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Gathering test coverage
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-----------------------
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## Gathering test coverage
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For either host or target coverage, you must first:
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@ -319,8 +310,7 @@ First, build and run the host tests as usual (see above).
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The coverage report is now available at `covreport/index.html`.
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Attaching GDB to the tests
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--------------------------
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## Attaching GDB to the tests
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Bionic's test runner will run each test in its own process by default to prevent
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tests failures from impacting other tests. This also has the added benefit of
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@ -330,7 +320,6 @@ However, this also makes it difficult to run the tests under GDB. To prevent
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each test from being forked, run the tests with the flag `--no-isolate`.
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32-bit ABI bugs
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---------------
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## 32-bit ABI bugs
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See [32-bit ABI bugs](docs/32-bit-abi.md).
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