GNU Linker

Another ELF linker, gold, is now available in addition to ld, the existing GNU linker. gold is intended to be a drop-in replacement for ld, so ld's documentation is intended to be the reference documentation.

gold supports most of ld's features, except notable ones such as MRI-compatible linker scripts, cross-

reference reports (--cref), and various other minor options. It also provides significantly improved link time with very large C++ applications.

In Red Hat Developer Toolset, the gold linker is not enabled by default. Users can explicitly switch between ld and gold by using the alternatives mechanism.

A.3.1.1. New Features

Changes Since Red Hat Enterprise Linux 6.2

The following features have been added since the release of binutils included in Red Hat Enterprise Linux 6.2:

A new INPUT_SECTION_FLAGS keyword has been added to the linker script language. This keyword can be used to select input sections by section header flags.

A new SORT_BY_INIT_PRIORITY keyword has been added to the linker script language. This keyword can be used to sort sections by numerical value of the GCC init_priority attribute encoded in the section name.

Changes Since Red Hat Enterprise Linux 5.8

In addition to the above changes, the following features have been added since the release of the binutils included in Red Hat Enterprise Linux 5.8:

GNU/Linux targets now support the STB_GNU_UNIQUE symbol binding, a GNU extension to the standard set of ELF symbol bindings. The binding is passed on to the dynamic linker, which ensures that in the entire process there is only one symbol with the given name and type in use.

Note

The implementation of this feature depends on capabilities only found in newer versions of the glibc library. Consequently, this feature is currently available in Red Hat Developer Toolset for Red Hat Enterprise Linux 6.

A new command line option --no-export-dynamic has been added. This option can be used to undo the effect of the -E and --export-dynamic options.

A new command line option --warn-alternate-em has been added. This option can be used to display a warning if an ELF format object file uses an alternate machine code.

A new linker script function REGION_ALIAS has been added. This function can be used to create alias names of memory regions.

A new command line option -Ttext-segment address has been added for ELF-based targets. This option can be used to set the address of the first byte of the text segment.

A new linker script command INSERT has been added. This command can be used to augment the default script.

In a linker script input section, it is now possible to specify a file within an archive by using the

archive:file syntax.

The --sort-common command line option now accepts ascending and descending as optional arguments. This can be used to specify which sorting order to use.

A new command line option --build-id has been added for ELF-based targets. This option can be used to generate a unique per-binary identifier embedded in a note section.

A new command line option --default-script=file_name (or -dT file_name) has been added. This option can be used to specify a replacement for the built-in linker script.

A new command line option -Bsymbolic-functions has been added. When creating a shared library, this option will cause references to global function symbols to be bound to the definitions with the shared library, if such exist.

The new command line options --dynamic-list-cpp-new and --dynamic-list-data have been added, which can be used to modify the dynamic list.

A.3.1.2. Compatibility Changes

Changes Since Red Hat Enterprise Linux 6.2

The following changes have been made since the release of the binutils included in Red Hat Enterprise Linux 6.2:

The --copy-dt-needed-entries command line option is no longer enabled by default. Instead, -

-no-copy-dt-needed-entries is now the default option.

Evaluation of linker script expressions has been significantly improved. Note that this can negatively affect scripts that rely on undocumented behavior of the old expression evaluation.

Changes Since Red Hat Enterprise Linux 5.8

In addition to the above changes, the following changes have been made since the release of the binutils included in Red Hat Enterprise Linux 5.8:

The --add-needed command line option has been renamed to --copy-dt-needed-entries in order to avoid confusion with the --as-needed option.

For GNU/Linux systems, the linker no longer processes any relocations made against symbols of the

ST T _GNU_IFUNC type. Instead, it emits them into the resulting binary for processing by the loader.

Note

The implementation of this feature depends on capabilities only found in newer versions of the glibc library. Consequently, this feature is currently available in Red Hat Developer Toolset for Red Hat Enterprise Linux 6.

The --as-needed command line option has been adapted to link in a dynamic library in the following two cases:

1. if the dynamic library satisfies undefined symbols in regular objects, and

2. if the dynamic library satisfies undefined symbols in other dynamic libraries unless the library is already found in a DT_NEEDED entry of one of the libraries that are already linked.

The -l:file_name command line option now searches the library path for a file name called

A.3.2. GNU Assembler