docs/CommandGuide/gccld.pod

=pod

=head1 NAME

gccld - optimizing LLVM linker

=head1 SYNOPSIS

B<gccld> [I<options>] I<filename ...>

=head1 DESCRIPTION

The B<gccld> 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, B<gccld> is able to produce native code executables.

The B<gccld> utility is primarily used by the L<llvmgcc> and
L<llvmg++|llvmgxx> 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.

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

=head2 Search Order

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

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

The shared library extension may be I<.so>, I<.dyld>, I<.dll>, or something
different, depending upon the system.

The B<-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.

=head2 Link order

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.

=head2 Library Linkage

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.

=head2 Native code generation

The B<gccld> program has limited support for native code generation, when
using the B<-native> or B<-native-cbe> options.

=head1 OPTIONS

=over

=item B<-help>

Print a summary of command line options.

=item B<-o> I<filename>

Specify the output filename which will hold the linked bytecode.

=item B<-stats>

Print statistics.

=item B<-time-passes>

Record the amount of time needed for each pass and print it to standard
error.

=item B<-verify>

Verify each pass result.

=item B<-disable-opt>

Disable all link-time optimization passes.

=item B<-disable-inlining>

Do not run the inliner pass.

=item B<-L>I<directory>

Add directory to the list of directories to search when looking for
libraries.

=item B<-disable-internalize>

Do not mark all symbols as internal.

=item B<-internalize-public-api-file> I<filename>

Preserve the list of symbol names in the file filename.

=item B<-internalize-public-api-list> I<list>

Preserve the symbol names in list.

=item B<-l>I<library>

Specify libraries to include when linking the output file.  When linking,
B<gccld> will first attempt to load a file with the pathname B<library>.  If
that fails, it will then attempt to load libI<library>.bc, libI<library>.a, and
libI<library>.I<shared library extension>, in that order.

=item B<-link-as-library>

Link the .bc files together as a library, not an executable.

=item B<-native>

Generate a native machine code executable.

When generating native executables, B<gccld> first checks for a bytecode
version of the library and links it in, if necessary.  If the library is
missing, B<gccld> skips it.  Then, B<gccld> links in the same
libraries as native code.

In this way, B<gccld> 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.

=item B<-native-cbe>

Generate a native machine code executable with the LLVM C backend.
      
This option is identical to the B<-native> option, but uses the
C backend to generate code for the program instead of an LLVM native
code generator.

=item B<-s>

Strip symbol information from the generated executable.

=item B<-v>

Print information about actions taken.

=back

=head1 EXIT STATUS

If B<gccld> succeeds, it will exit with an exit status of 0.
Otherwise, if an error occurs, it will exit with a non-zero exit
status.

=head1 SEE ALSO

L<llvm-link|llvm-link>, L<gccas|gccas>

=head1 AUTHORS

Maintained by the LLVM Team (L<http://llvm.cs.uiuc.edu>).

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