Evgeniy Stepanov cd15bacf33 Fix segv when unwinding stack past __libc_init.
This change fixes a segmentation fault in the libc unwinder when it goes
past __libc_init.

Unwind instructions for __libc_init direct it to grab the return address from
the stack frame. Without this change, the unwinder gets a wild address and
looks up further unwind instructions for the routine at that address. If it's
unlucky enough to hit an existing function, it will try to unwind it. Bad
things happen then.

With this change, the return address always points to the _start function,
which does not have unwind instructions associated with it. This stop the
unwind process.

__libc_init never returns, so this does not affect program execution, other
than adding 4 bytes on the main thread stack.

Change-Id: Id58612172e8825c8729cccd081541a13bff96bd0
2012-04-10 16:45:54 +04:00
..
2012-02-01 09:46:08 -08:00
2010-12-20 15:58:06 +01:00
2011-06-09 13:03:17 -07:00
2012-03-09 11:50:46 -08:00
2012-04-02 07:43:15 -07:00
2012-04-02 07:43:15 -07:00
2010-10-19 15:12:40 -07:00

Welcome to Bionic, Android's small and custom C library for the Android
platform.

Bionic is mainly a port of the BSD C library to our Linux kernel with the
following additions/changes:

- no support for locales
- no support for wide chars (i.e. multi-byte characters)
- its own smallish implementation of pthreads based on Linux futexes
- support for x86, ARM and ARM thumb CPU instruction sets and kernel interfaces

Bionic is released under the standard 3-clause BSD License

Bionic doesn't want to implement all features of a traditional C library, we only
add features to it as we need them, and we try to keep things as simple and small
as possible. Our goal is not to support scaling to thousands of concurrent threads
on multi-processors machines; we're running this on cell-phones, damnit !!

Note that Bionic doesn't provide a libthread_db or a libm implementation.


Adding new syscalls:
====================

Bionic provides the gensyscalls.py Python script to automatically generate syscall
stubs from the list defined in the file SYSCALLS.TXT. You can thus add a new syscall
by doing the following:

- edit SYSCALLS.TXT
- add a new line describing your syscall, it should look like:

   return_type  syscall_name(parameters)    syscall_number

- in the event where you want to differentiate the syscall function from its entry name,
  use the alternate:

   return_type  funcname:syscall_name(parameters)  syscall_number

- additionally, if the syscall number is different between ARM and x86, use:

   return_type  funcname[:syscall_name](parameters)   arm_number,x86_number

- a syscall number can be -1 to indicate that the syscall is not implemented on
  a given platform, for example:

   void   __set_tls(void*)   arm_number,-1


the comments in SYSCALLS.TXT contain more information about the line format

You can also use the 'checksyscalls.py' script to check that all the syscall
numbers you entered are correct. It does so by looking at the values defined in
your Linux kernel headers. The script indicates where the values are incorrect
and what is expected instead.