ldflags

LDFLAGS is an environment variable used by compilers and linkers to specify flags for the linking stage of building software. It is intended to influence the behavior of the linker, such as locating libraries and configuring linkage, rather than affecting the compilation of source files. It is commonly used alongside other variables like CFLAGS (compile-time flags) and LIBS (libraries to link against).

Common uses of LDFLAGS include adding library search paths, linking against specific libraries, and setting runtime link behavior. For example, LDFLAGS="-L/usr/local/lib -Wl,-rpath,/usr/local/lib" adds /usr/local/lib to the linker’s search path and embeds a runtime library path so the dynamic linker can find the libraries at runtime. Another example is including -static or -shared to influence whether the linker performs static or shared linkage. The -Wl, option can be used to pass flags directly to the linker, such as LDFLAGS="-Wl,--as-needed".

Differentiating LDFLAGS from other variables is important. LIBS typically contains library names (such as -lm or -ldl), while -L directives and other linker options belong in LDFLAGS. Some build systems allow placing library names in LIBS as well, but LDFLAGS is the conventional container for linker options that affect the linking process as a whole.

Cross-compilation and sysroot considerations often appear in LDFLAGS, with settings like --sysroot=DIR and appropriate -L and -l paths to locate target libraries for the intended target environment.

In practice, LDFLAGS is set in the environment or a Makefile to ensure the linker receives the desired options during the final linking step, shaping how executables and libraries are produced.