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README

      1 Welcome to Bionic, Android's small and custom C library for the Android
      2 platform.
      3 
      4 Bionic is mainly a port of the BSD C library to our Linux kernel with the
      5 following 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 
     12 Bionic is released under the standard 3-clause BSD License
     13 
     14 Bionic doesn't want to implement all features of a traditional C library, we only
     15 add features to it as we need them, and we try to keep things as simple and small
     16 as possible. Our goal is not to support scaling to thousands of concurrent threads
     17 on multi-processors machines; we're running this on cell-phones, damnit !!
     18 
     19 Note that Bionic doesn't provide a libthread_db or a libm implementation.
     20 
     21 
     22 Adding new syscalls:
     23 ====================
     24 
     25 Bionic provides the gensyscalls.py Python script to automatically generate syscall
     26 stubs from the list defined in the file SYSCALLS.TXT. You can thus add a new syscall
     27 by 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 
     49 the comments in SYSCALLS.TXT contain more information about the line format
     50 
     51 You can also use the 'checksyscalls.py' script to check that all the syscall
     52 numbers you entered are correct. It does so by looking at the values defined in
     53 your Linux kernel headers. The script indicates where the values are incorrect
     54 and what is expected instead.
     55