Linux Linker Environment Variables

LD_PRELOAD

• Points the dynamic linker at a library path that should load before other libraries.
• Symbols and functions from that preloaded library override later-linked ones with the same names.
• Useful for redirecting shared-library calls and applying runtime patches.

LD_SHOW_AUXV

• Tells the program loader to print the process auxiliary vector while the program runs.
• The auxiliary vector sits on the program stack (placed by the kernel's ELF loading path) and carries process-specific data into the dynamic linker.
• That data is useful for reversing and debugging.

• For the memory address of the VDSO page in the process image, check AT_SYSINFO.

Linker scripts

• The linker reads a linker script to decide section layout, memory, and symbols.
• Dump the default script with ld -verbose.
• ld interprets the script when it takes inputs such as relocatable objects, shared libraries, and headers.
• The script says how to build the output (for example an executable).
• For an ELF executable, it controls placement and which sections land in which segments.
• .bss always ends up at the end of the data segment because the linker script puts it there.
• Understanding the link step during compilation matters: gcc leans on the linker and other tools for that work.
• Being able to steer executable layout is a practical control point, not a curiosity.