NAME

llvm-ld - LLVM linker

SYNOPSIS

llvm-ld <options> <files>

DESCRIPTION

The llvm-ld tool takes a set of LLVM bitcode files and links them together into a single LLVM bitcode file. The output bitcode file can be another bitcode file or an executable bitcode program. Using additional options, llvm-ld is able to produce native code executables.

The llvm-ld tool is the main linker for LLVM. It is used to link together the output of LLVM front-end compilers and run ``link time'' optimizations (mostly the inter-procedural kind).

The llvm-ld tools attempts to mimic the interface provided by the default system linker so that it can act as a drop-in replacement.

Search Order

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

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

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

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.

Link order

All object and bitcode 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.

Library Linkage

Object files and static bitcode 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.

Native code generation

The llvm-ld program has limited support for native code generation, when using the -native or -native-cbe options. Native code generation is performed by converting the linked bitcode into native assembly (.s) or C code and running the system compiler (typically gcc) on the result.

OPTIONS

General Options

-help

Print a summary of command line options.

-v

Specifies verbose mode. In this mode the linker will print additional information about the actions it takes, programs it executes, etc.

-stats

Print statistics.

-time-passes

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

Input/Output Options

-o filename

This overrides the default output file and specifies the name of the file that should be generated by the linker. By default, llvm-ld generates a file named a.out for compatibility with ld. The output will be written to filename.

-lname

This option specifies the name of a library to search when resolving symbols for the program. Only the base name should be specified as name, without a lib prefix or any suffix.

-LPath

This option tells llvm-ld to look in Path to find any library subsequently specified with the -l option. The paths will be searched in the order in which they are specified on the command line. If the library is still not found, a small set of system specific directories will also be searched. Note that libraries specified with the -l option that occur before any -L options will not search the paths given by the -L options following it.

-link-as-library

Link the bitcode files together as a library, not an executable. In this mode, undefined symbols will be permitted.

-r

An alias for -link-as-library.

-march=target

Specifies the kind of machine for which code or assembly should be generated.

-native

Generate a native machine code executable.

When generating native executables, llvm-ld first checks for a bitcode version of the library and links it in, if necessary. If the library is missing, llvm-ld skips it. Then, llvm-ld links in the same libraries as native code.

In this way, llvm-ld should be able to link in optimized bitcode subsets of common libraries and then link in any part of the library that hasn't been converted to bitcode.

-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.

Optimization Options

-O0

An alias for the -O1 option.

-O1

Optimize for linking speed, not execution speed. The optimizer will attempt to reduce the size of the linked program to reduce I/O but will not otherwise perform any link-time optimizations.

-O2

Perform only the minimal or required set of scalar optimizations.

-03

An alias for the -O2 option.

-04

Perform the standard link time inter-procedural optimizations. This will attempt to optimize the program taking the entire program into consideration.

-O5

Perform aggressive link time optimizations. This is the same as -O4 but works more aggressively to optimize the program.

-disable-inlining

Do not run the inlining pass. Functions will not be inlined into other functions.

-disable-opt

Completely disable optimization. The various -On options will be ignored and no link time optimization passes will be run.

-disable-internalize

Do not mark all symbols as internal.

-verify-each

Run the verification pass after each of the passes to verify intermediate results.

-strip-all

Strip all debug and symbol information from the executable to make it smaller.

-strip-debug

Strip all debug information from the executable to make it smaller.

-s

An alias for -strip-all.

-S

An alias for -strip-debug.

-export-dynamic

An alias for -disable-internalize

-load module

Load an optimization module, module, which is expected to be a dynamic library that provides the function name RunOptimizations. This function will be passed the PassManager, and the optimization level (values 0-5 based on the -On option). This function may add passes to the PassManager that should be run. This feature allows the optimization passes of llvm-ld to be extended.

-post-link-optPath

Run post-link optimization program. After linking is completed a bitcode file will be generated. It will be passed to the program specified by Path as the first argument. The second argument to the program will be the name of a temporary file into which the program should place its optimized output. For example, the ``no-op optimization'' would be a simple shell script:

    #!/bin/bash
    cp $1 $2

EXIT STATUS

If llvm-ld succeeds, it will exit with 0 return code. If an error occurs, it will exit with a non-zero return code.

ENVIRONMENT

The LLVM_LIB_SEARCH_PATH environment variable is used to find bitcode libraries. Any paths specified in this variable will be searched after the -L options.

SEE ALSO

llvm-link

AUTHORS

Maintained by the LLVM Team (http://llvm.org).