README
1Welcome to Bionic, Android's small and custom C library for the Android
2platform.
3
4Bionic is mainly a port of the BSD C library to our Linux kernel with the
5following additions/changes:
6
7- no support for locales
8- no support for wide chars (i.e. multi-byte characters)
9- its own smallish implementation of pthreads based on Linux futexes
10- support for x86, ARM and ARM thumb CPU instruction sets and kernel interfaces
11
12Bionic is released under the standard 3-clause BSD License
13
14Bionic doesn't want to implement all features of a traditional C library, we only
15add features to it as we need them, and we try to keep things as simple and small
16as possible. Our goal is not to support scaling to thousands of concurrent threads
17on multi-processors machines; we're running this on cell-phones, damnit !!
18
19Note that Bionic doesn't provide a libthread_db or a libm implementation.
20
21
22Adding new syscalls:
23====================
24
25Bionic provides the gensyscalls.py Python script to automatically generate syscall
26stubs from the list defined in the file SYSCALLS.TXT. You can thus add a new syscall
27by doing the following:
28
29- edit SYSCALLS.TXT
30- add a new line describing your syscall, it should look like:
31
32 return_type syscall_name(parameters) syscall_number
33
34- in the event where you want to differentiate the syscall function from its entry name,
35 use the alternate:
36
37 return_type funcname:syscall_name(parameters) syscall_number
38
39- additionally, if the syscall number is different between ARM and x86, use:
40
41 return_type funcname[:syscall_name](parameters) arm_number,x86_number
42
43- a syscall number can be -1 to indicate that the syscall is not implemented on
44 a given platform, for example:
45
46 void __set_tls(void*) arm_number,-1
47
48
49the comments in SYSCALLS.TXT contain more information about the line format
50
51You can also use the 'checksyscalls.py' script to check that all the syscall
52numbers you entered are correct. It does so by looking at the values defined in
53your Linux kernel headers. The script indicates where the values are incorrect
54and what is expected instead.
55