forked from OSchip/llvm-project
176 lines
5.0 KiB
Plaintext
176 lines
5.0 KiB
Plaintext
=pod
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=head1 NAME
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gccld - optimizing LLVM linker
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=head1 SYNOPSIS
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B<gccld> [I<options>] I<filename ...>
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=head1 DESCRIPTION
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The B<gccld> utility takes a set of LLVM bytecode files and links them
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together into a single LLVM bytecode file. The output bytecode file can be
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another bytecode library or an executable bytecode program. Using additional
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options, B<gccld> is able to produce native code executables.
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The B<gccld> utility is primarily used by the L<llvmgcc> and
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L<llvmg++|llvmgxx> front-ends, and as such, attempts to mimic the interface
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provided by the default system linker so that it can act as a ``drop-in''
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replacement.
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The B<gccld> tool performs a small set of interprocedural, post-link
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optimizations on the program.
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=head2 Search Order
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When looking for objects specified on the command line, B<gccld> will search for
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the object first in the current directory and then in the directory specified by
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the B<LLVM_LIB_SEARCH_PATH> environment variable. If it cannot find the object,
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it fails.
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When looking for a library specified with the B<-l> option, B<gccld> first
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attempts to load a file with that name from the current directory. If that
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fails, it looks for libI<library>.bc, libI<library>.a, or libI<library>.I<shared
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library extension>, in that order, in each directory added to the library search
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path with the B<-L> option. These directories are searched in the order they
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were specified. If the library cannot be located, then B<gccld> looks in the
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directory specified by the B<LLVM_LIB_SEARCH_PATH> environment variable. If it
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does not find a library there, it fails.
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The shared library extension may be I<.so>, I<.dyld>, I<.dll>, or something
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different, depending upon the system.
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The B<-L> option is global. It does not matter where it is specified in the
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list of command line arguments; the directory is simply added to the search path
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and is applied to all libraries, preceding or succeeding, in the command line.
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=head2 Link order
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All object files are linked first in the order they were specified on the
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command line. All library files are linked next. Some libraries may not be
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linked into the object program; see below.
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=head2 Library Linkage
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Object files and static bytecode objects are always linked into the output
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file. Library archives (.a files) load only the objects within the archive
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that define symbols needed by the output file. Hence, libraries should be
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listed after the object files and libraries which need them; otherwise, the
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library may not be linked in, and the dependent library will not have its
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undefined symbols defined.
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=head2 Native code generation
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The B<gccld> program has limited support for native code generation, when
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using the B<-native> or B<-native-cbe> options.
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=head1 OPTIONS
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=over
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=item B<-help>
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Print a summary of command line options.
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=item B<-o> I<filename>
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Specify the output filename which will hold the linked bytecode.
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=item B<-stats>
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Print statistics.
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=item B<-time-passes>
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Record the amount of time needed for each pass and print it to standard
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error.
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=item B<-verify>
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Verify each pass result.
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=item B<-disable-opt>
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Disable all link-time optimization passes.
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=item B<-disable-inlining>
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Do not run the inliner pass.
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=item B<-L>I<directory>
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Add directory to the list of directories to search when looking for
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libraries.
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=item B<-disable-internalize>
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Do not mark all symbols as internal.
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=item B<-internalize-public-api-file> I<filename>
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Preserve the list of symbol names in the file filename.
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=item B<-internalize-public-api-list <list>>
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Preserve the symbol names in list.
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=item B<-l>I<library>
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Specify libraries to include when linking the output file. When linking,
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B<gccld> will first attempt to load a file with the pathname B<library>. If
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that fails, it will then attempt to load libI<library>.bc, libI<library>.a, and
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libI<library>.I<shared library extension>, in that order.
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=item B<-link-as-library>
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Link the .bc files together as a library, not an executable.
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=item B<-native>
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Generate a native machine code executable.
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When generating native executables, B<gccld> first checks for a bytecode
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version of the library and links it in, if necessary. If the library is
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missing, B<gccld> skips it. Then, B<gccld> links in the same
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libraries as native code.
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In this way, B<gccld> should be able to link in optimized bytecode
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subsets of common libraries and then link in any part of the library that
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hasn't been converted to bytecode.
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=item B<-native-cbe>
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Generate a native machine code executable with the LLVM C backend.
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This option is identical to the B<-native> option, but uses the
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C backend to generate code for the program instead of an LLVM native
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code generator.
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=item B<-s>
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Strip symbol information from the generated executable.
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=item B<-v>
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Print information about actions taken.
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=back
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=head1 EXIT STATUS
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If B<gccld> succeeds, it will exit with an exit status of 0.
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Otherwise, if an error occurs, it will exit with a non-zero exit
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status.
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=head1 SEE ALSO
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L<llvm-link|llvm-link>, L<gccas|gccas>
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=head1 AUTHORS
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Maintained by the LLVM Team (L<http://llvm.cs.uiuc.edu>).
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=cut
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