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* README: Rewrite, with some notes on unsupported features.

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Ian Lance Taylor 2008-03-25 21:14:45 +00:00
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2008-03-25 Ian Lance Taylor <iant@google.com>
* README: Rewrite, with some notes on unsupported features.
2008-03-24 Cary Coutant <ccoutant@google.com>
* i386.cc (Target_i386::Got_type): New enum declaration.

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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.
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.
It is written in C++. It is (intended to be) a GNU program, and
therefore follows the GNU formatting standards as modified for C++.
Source documents in order of precedence:
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
* linker map files (-M, -Map)
* cross-reference reports (--cref)
* linker garbage collection (--gc-sections)
* position independent executables (-pie)
* 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,
which still supporting the normal case of native linking as fast as
possible. This makes the code more complex.
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.
Many functions are actually templates whose parameter is the ELF file
class (e.g., 32 bits or 64 bits). The code is the same, but we don't
want to pay the execution time cost of always using 64-bit integers if
the target is 32 bits.
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.