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gold is an ELF linker. It is intended to have complete support for
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ELF and to run as fast as possible on modern systems. For normal use
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it is a drop-in replacement for the older GNU linker.
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gold is part of the GNU binutils. See ../binutils/README for more
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general notes, including where to send bug reports.
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gold was originally developed at Google, and was contributed to the
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Free Software Foundation in March 2008. At Google it was designed by
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Ian Lance Taylor, with major contributions by Cary Coutant, Craig
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Silverstein, and Andrew Chatham.
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The existing GNU linker manual is intended to be accurate
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documentation for features which gold supports. gold supports most of
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the features of the GNU linker for ELF targets. Notable
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omissions--features of the GNU linker not currently supported in
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gold--are:
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* MRI compatible linker scripts
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* cross-reference reports (--cref)
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* various other minor options
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Notes on the code
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=================
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These are some notes which may be helpful to people working on the
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source code of gold itself.
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gold is written in C++. It is a GNU program, and therefore follows
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the GNU formatting standards as modified for C++. Source documents in
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order of decreasing precedence:
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http://www.gnu.org/prep/standards/
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http://gcc.gnu.org/onlinedocs/libstdc++/17_intro/C++STYLE
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http://www.zembu.com/eng/procs/c++style.html
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The linker is intended to have complete support for cross-compilation,
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while still supporting the normal case of native linking as fast as
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possible. In order to do this, many classes are actually templates
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whose parameter is the ELF file class (e.g., 32 bits or 64 bits). The
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C++ code is the same, but we don't pay the execution time cost of
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always using 64-bit integers if the target is 32 bits. Many of these
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class templates also have an endianness parameter: true for
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big-endian, false for little-endian.
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The linker is multi-threaded. The Task class represents a single unit
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of work. Task objects are stored on a single Workqueue object. Tasks
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communicate via Task_token objects. Task_token objects are only
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manipulated while holding the master Workqueue lock. Relatively few
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mutexes are used.
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Build requirements
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==================
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The gold source code uses templates heavily. Building it requires a
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recent version of g++. g++ 4.0.3 and 4.1.3 are known to work. g++
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3.2, 3.4.3, and 4.1.2 are known to fail.
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The linker script parser uses features which are only in newer
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versions of bison. bison 2.3 is known to work. bison 1.26 is known
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to fail. If you are building gold from an official binutils release,
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the bison output should already be included.
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