llvm/docs/CommandGuide/gccld.html

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<title>LLVM: gccld tool</title>

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<center><h1>LLVM: <tt>gccld</tt> tool</h1></center>
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<h3>NAME</h3>
<tt>gccld</tt>

<h3>SYNOPSIS</h3>
<tt>gccld [options] &lt; filename&gt; [ filename ...]</tt>

<h3>DESCRIPTION</h3>

The <tt>gccld</tt> utility takes a set of LLVM bytecode files and links them
together into a single LLVM bytecode file.  The output bytecode file can be
another bytecode library or an executable bytecode program.  Using additional
options, <tt>gccld</tt> is able to produce native code executables.
<p>

The <tt>gccld</tt> utility is primarily used by the <a href="llvmgcc.html">C</a>
and <a href="llvmgxx.html">C++</a> front-ends, and as such, attempts to mimic
the interface provided by the default system linker so that it can act as a
"drop-in" replacement.
<p>

The <tt>gccld</tt> tool performs a small set of interprocedural, post-link,
optimizations on the program.


<h4>Search Order</h4>

<p>
When looking for objects specified on the command line, <tt>gccld</tt> will
search for the object first in the current directory and then in the directory
specified by the <tt>LLVM_LIB_SEARCH_PATH</tt> environment variable.  If it
cannot find the object, it fails.
</p>

<p>
When looking for a library specified with the -l option, <tt>gccld</tt> first
attempts to load a file with that name from the current directory.  If that
fails, it looks for lib&lt;library&gt;.bc, lib&lt;library&gt;.a, or
lib&lt;library&gt;.&lt;shared library extension&gt;, in that order, in each
directory added to the library search path with the -L option.  These
directories are searched in the order they
were specified.  If the library cannot be located, then <tt>gccld</tt> looks in
the directory specified by the <tt>LLVM_LIB_SEARCH_PATH</tt> environment
variable.  If it does not find a library there, it fails.
</p>

<p>
The shared library extension is usually <tt>.so</tt>, but it may differ
depending upon the system.
</p>

<p>
The -L option is global.  It does not matter where it is specified in the list
of command line arguments; the directory is simply added to the search path and
is applied to all libraries, preceding or succeeding, in the command line.
</p>

<h4>Link order</h4>

All object files are linked first in the order they were specified on the
command line.  All library files are linked next.  Some libraries may not be
linked into the object program; see below.

<h4>Library Linkage</h4>

Object files and static bytecode objects are always linked into the output
file.  Library archives (.a files) load only the objects within the archive
that define symbols needed by the output file.  Hence, libraries should be
listed after the object files and libraries which need them; otherwise, the
library may not be linked in, and the dependent library will not have its
undefined symbols defined.

<h4>Native code generation</h4>

The <tt>gccld</tt> program has limited support for native code generation, when
using the -native option.


<h3>OPTIONS</h3>

<ul>
	<li> -help
	<br>
	Print a summary of command line options.
	<p>

	<li> -o &lt;filename&gt;
	<br>
	Specify the output filename which will hold the linked bytecode.
	<p>

	<li> -stats
	<br>
	Print statistics.
	<p>

	<li> -time-passes
	<br>
	Record the amount of time needed for each pass and print it to standard
	error.
	<p>

	<li> -verify
	<br>
	Verify each pass result.
	<p>

	<li> -disable-opt
	<br>
  Disable all link-time optimization passes.
	<p>

	<li> -disable-inlining
	<br>
  Do not run the inliner pass.
	<p>

	<li> -L=&lt;directory&gt;
	<br>
	Add directory to the list of directories to search when looking for
	libraries.
	<p>

	<li> -disable-internalize
	<br>
	Do not mark all symbols as internal.
	<p>

	<li> -internalize-public-api-file &lt;filename&gt;
	<br>
	Preserve the list of symbol names in the file filename.
	<p>

	<li> -internalize-public-api-list &lt;list&gt;
	<br>
	Preserve the symbol names in list.
	<p>

	<li> -l=&lt;library&gt;
	<br>
	Specify libraries to include when linking the output file.  When
	linking, <tt>gccld</tt> will first attempt to load a file with the
	pathname <tt>library</tt>.  If that fails, it will then attempt to load
	lib&lt;library&gt;.bc, lib&lt;library&gt;.a, and
  lib&lt;library&gt;.&lt;shared library extension&gt;, in that order.
	<p>

	<li> -link-as-library
	<br>
	Link the .bc files together as a library, not an executable.
	<p>

	<li> -native
	<br>
	Generate a native, machine code executable.
  <p>
  When generating native executables, <tt>gccld</tt> first checks for a bytecode
  version of the library and links it in, if necessary.  If the library is
  missing, <tt>gccld</tt> skips it.  Then, <tt>gccld</tt> links in the same
  libraries as native code.
  <p>
  In this way, <tt>gccld</tt> should be able to link in optimized bytecode
  subsets of common libraries and then link in any part of the library that
  hasn't been converted to bytecode.
	<p>

	<li> -s
	<br>
	Strip symbol information from the generated executable.
	<p>

	<li> -v
	<br>
	Print information about actions taken.
</ul>

<h3>EXIT STATUS</h3>

If <tt>gccld</tt> succeeds, it will exit with 0.  Otherwise, if an error occurs,
it will exit with a non-zero value.

<h3>SEE ALSO</h3>
<a href="llvm-link.html"><tt>llvm-link</tt></a>
<a href="gccas.html"><tt>gccas</tt></a>

<h3>BUGS</h3>
The -L option cannot be used for find native code libraries when using the
-native option.

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Maintained by the <a href="http://llvm.cs.uiuc.edu">LLVM Team</a>.
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