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gold is an ELF linker.  It is intended to have complete support for

ELF and to run as fast as possible on modern systems.  For normal use

it is a drop-in replacement for the older GNU linker.

gold is part of the GNU binutils.  See ../binutils/README for more

general notes, including where to send bug reports.

gold was originally developed at Google, and was contributed to the

Free Software Foundation in March 2008.  At Google it was designed by

Ian Lance Taylor, with major contributions by Cary Coutant, Craig

Silverstein, and Andrew Chatham.

The existing GNU linker manual is intended to be accurate

documentation for features which gold supports.  gold supports most of

the features of the GNU linker for ELF targets.  Notable

omissions--features of the GNU linker not currently supported in

gold--are:

  * MEMORY regions in linker scripts

  * MRI compatible linker scripts

  * cross-reference reports (--cref)

  * various other minor options

Notes on the code

=================

These are some notes which may be helpful to people working on the

source code of gold itself.

gold is written in C++.  It is a GNU program, and therefore follows

the GNU formatting standards as modified for C++.  Source documents in

order of decreasing precedence:

    http://www.gnu.org/prep/standards/

    http://gcc.gnu.org/onlinedocs/libstdc++/17_intro/C++STYLE

    http://www.zembu.com/eng/procs/c++style.html

The linker is intended to have complete support for cross-compilation,

while still supporting the normal case of native linking as fast as

possible.  In order to do this, many classes are actually templates

whose parameter is the ELF file class (e.g., 32 bits or 64 bits).  The

C++ code is the same, but we don't pay the execution time cost of

always using 64-bit integers if the target is 32 bits.  Many of these

class templates also have an endianness parameter: true for

big-endian, false for little-endian.

The linker is multi-threaded.  The Task class represents a single unit

of work.  Task objects are stored on a single Workqueue object.  Tasks

communicate via Task_token objects.  Task_token objects are only

manipulated while holding the master Workqueue lock.  Relatively few

mutexes are used.

Build requirements

==================

The gold source code uses templates heavily.  Building it requires a

recent version of g++.  g++ 4.0.3 is known to work.  g++ 3.2 and g++

3.4.3 are known to fail.

The linker script parser uses features which are only in newer

versions of bison.  bison 2.3 is known to work.  bison 1.26 is known

to fail.  If you are building gold from an official binutils release,

the bison output should already be included.