UNIX BUILD NOTES
====================
Some notes on how to build twister in Unix. 

To Build
---------------------

	./bootstrap.sh
	make

Dependencies
---------------------

 Library     Purpose           Description
 -------     -------           -----------
 libssl      SSL Support       Secure communications
 libdb4.8    Berkeley DB       Blockchain & wallet storage
 libboost    Boost             C++ Library

IPv6 support may be disabled by setting:

	USE_IPV6=0    Disable IPv6 support

Licenses of statically linked libraries:
 Berkeley DB   New BSD license with additional requirement that linked
               software must be free open source
 Boost         MIT-like license

- Versions used in this release:
-  GCC           4.3.3
-  OpenSSL       1.0.1c
-  Berkeley DB   4.8.30.NC
-  Boost         1.37

Dependency Build Instructions: Ubuntu & Debian
----------------------------------------------
Build requirements:

	sudo apt-get install build-essential
	sudo apt-get install libssl-dev

for Ubuntu 12.04:

	sudo apt-get install libboost-all-dev

 db4.8 packages are available [here](https://launchpad.net/~bitcoin/+archive/bitcoin).

 Ubuntu precise has packages for libdb5.1-dev and libdb5.1++-dev,
 but using these will break binary wallet compatibility, and is not recommended.

for other Ubuntu & Debian:

	sudo apt-get install libdb4.8-dev
	sudo apt-get install libdb++-dev
	sudo apt-get install libboost-all-dev
	
 (If using Boost 1.37, append -mt to the boost libraries in the makefile)


Dependency Build Instructions: Gentoo
-------------------------------------

Note: If you just want to install bitcoind on Gentoo, you can add the Bitcoin overlay and use your package manager:

	layman -a bitcoin && emerge bitcoind
	emerge -av1 --noreplace boost glib openssl sys-libs/db:4.8

Take the following steps to build (no UPnP support):

	cd ${BITCOIN_DIR}/src
	make -f makefile.unix USE_IPV6=1 BDB_INCLUDE_PATH='/usr/include/db4.8'
	strip bitcoind


Notes
-----
The release is built with GCC and then "strip bitcoind" to strip the debug
symbols, which reduces the executable size by about 90%.


Berkeley DB
-----------
You need Berkeley DB 4.8.  If you have to build Berkeley DB yourself:

	../dist/configure --enable-cxx
	make


Boost
-----
If you need to build Boost yourself:

	sudo su
	./bootstrap.sh
	./bjam install


Security
--------
To help make your bitcoin installation more secure by making certain attacks impossible to
exploit even if a vulnerability is found, you can take the following measures:

* Position Independent Executable
    Build position independent code to take advantage of Address Space Layout Randomization
    offered by some kernels. An attacker who is able to cause execution of code at an arbitrary
    memory location is thwarted if he doesn't know where anything useful is located.
    The stack and heap are randomly located by default but this allows the code section to be
    randomly located as well.

    On an Amd64 processor where a library was not compiled with -fPIC, this will cause an error
    such as: "relocation R_X86_64_32 against `......' can not be used when making a shared object;"

    To build with PIE, use:

    	make -f makefile.unix ... -e PIE=1

    To test that you have built PIE executable, install scanelf, part of paxutils, and use:

    	scanelf -e ./bitcoin

    The output should contain:
     TYPE
    ET_DYN

* Non-executable Stack
    If the stack is executable then trivial stack based buffer overflow exploits are possible if
    vulnerable buffers are found. By default, bitcoin should be built with a non-executable stack
    but if one of the libraries it uses asks for an executable stack or someone makes a mistake
    and uses a compiler extension which requires an executable stack, it will silently build an
    executable without the non-executable stack protection.

    To verify that the stack is non-executable after compiling use:
    `scanelf -e ./bitcoin`

    the output should contain:
	STK/REL/PTL
	RW- R-- RW-

    The STK RW- means that the stack is readable and writeable but not executable.