LLVM: `gccld` tool

NAME

gccld

SYNOPSIS

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

DESCRIPTION

The 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, gccld is able to produce native code executables.

The gccld utility is primarily used by the C and C++ 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 gccld tool performs a small set of interprocedural, post-link, optimizations on the program.

Search Order

When looking for objects specified on the command line, gccld 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, gccld first attempts to load a file with that name from the current directory. If that fails, it looks for lib<library>.bc, lib<library>.a, or lib<library>.<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 were specified. If the library cannot be located, then gccld 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 is usually .so, but it may differ 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 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 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.

Native code generation

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

OPTIONS

-help
Print a summary of command line options.
-o <filename>
Specify the output filename which will hold the linked bytecode.
-stats
Print statistics.
-time-passes
Record the amount of time needed for each pass and print it to standard error.
-verify
Verify each pass result.
-disable-opt
Disable all link-time optimization passes.
-disable-inlining
Do not run the inliner pass.
-L=<directory>
Add directory to the list of directories to search when looking for libraries.
-disable-internalize
Do not mark all symbols as internal.
-internalize-public-api-file <filename>
Preserve the list of symbol names in the file filename.
-internalize-public-api-list <list>
Preserve the symbol names in list.
-l=<library>
Specify libraries to include when linking the output file. When linking, gccld will first attempt to load a file with the pathname library. If that fails, it will then attempt to load lib<library>.bc, lib<library>.a, and lib<library>.<shared library extension>, in that order.
-link-as-library
Link the .bc files together as a library, not an executable.
-native
Generate a native, machine code executable.
When generating native executables, gccld first checks for a bytecode version of the library and links it in, if necessary. If the library is missing, gccld skips it. Then, gccld links in the same libraries as native code.
In this way, 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.
-s
Strip symbol information from the generated executable.
-v
Print information about actions taken.

EXIT STATUS

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

BUGS

The -L option cannot be used for find native code libraries when using the -native option.

Maintained by the LLVM Team.

LLVM: gccld tool