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

1 files changed, 45 insertions, 10 deletions

diff --git a/gold/README b/gold/README
index aa318f2daa..49de60ad87 100644
--- a/gold/README
+++ b/gold/README
@@ -1,18 +1,53 @@
 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.