ld

Additional Notes

ld is the GNU linker that takes one or more object files produced by a compiler (such as gcc), resolves symbol references, relocates code, and produces an executable, shared library, or object file. It is the final stage of the compilation pipeline.

In practice, developers rarely invoke ld directly. The compiler driver (e.g., gcc or clang) calls ld behind the scenes with the correct arguments. Direct use of ld is needed for low-level tasks such as linkers scripts, bootloaders, kernel modules, or embedded development where full control over memory layout is required.

Syntax

ld [options] object-files...

Parameters

• object-files: One or more .o files, static libraries (.a), or shared objects (.so) to link.

Common Options

• -o file: Set the output file name.
• -l library: Link against a library (e.g., -lm for libm).
• -L path: Add a directory to the library search path.
• -shared: Create a shared library instead of an executable.
• -r, --relocateable: Produce a relocatable object file (partial linking).
• -e symbol: Set the entry point symbol.
• -T script, --script script: Use a custom linker script.
• -Map file: Write a link map to the specified file.
• -static: Produce a statically linked binary.
• -pie: Produce a position-independent executable.
• --gc-sections: Remove unused sections from the output.
• -M: Print the link map to stdout.
• -v: Display version and show the linker emulation.

Examples

ld -o hello hello.o -lc

Link hello.o with the C library to produce an executable called hello.

ld -shared -o libfoo.so foo.o bar.o

Create a shared library from two object files.

ld -r -o combined.o part1.o part2.o

Partially link two object files into a single relocatable object.

ld -T kernel.ld -o kernel.bin boot.o main.o

Link kernel object files using a custom linker script.

ld -Map output.map -o program prog.o -lc

Generate a link map file showing symbol addresses and section layout.

Practical Notes

• Use gcc -v or gcc -Wl,--verbose to see the linker commands that the compiler generates. This helps when you need to reproduce or customize linker behavior.
• Linker scripts (.ld files) control the layout of sections, memory regions, and symbol addresses. They are essential for embedded and OS development.
• The -l flag searches for lib<name>.so or lib<name>.a in the standard library paths and any paths added with -L.
• Use ldd to inspect which shared libraries a linked binary depends on.
• The collect2 tool wraps ld on many systems; calling ld directly bypasses constructor/destructor handling.