I recently needed to generate an ELF binary with both RPATH and RUNPATH entries. I could not figure out how to produce this using linker command line arguments.

I was considering attempting a linker script, but first I switched to my Lisp REPL buffer ¹ and found that (ql:quickload "elf") loaded a promising-looking Common Lisp ELF library.

I created a stub library with RPATH using gcc and an empty C file, then loaded it with (elf:read-elf).

With the SLIME inspector (M-x slime-inspect) I could traverse the structure of the ELF headers. I eventually found the RPATH entry.

In the REPL I built up a function to search for RPATH then push a new RUNPATH entry alongside it.

It turned out the ELF library had no support for the RUNPATH entry, so I redefined its dyn-tag dictionary to include it.

After adding RUNPATH, I wrote the modified ELF structures to a file using (elf:write-elf). The generated ELF file sufficed for the test case.

I thought this was an interesting use case to share, demonstrating unique properties of the Lisp environment. I published the result (I realize now I should have written generate-example-library.sh in Lisp instead of shell!; oh well).

1. Which I have been trying to keep open lately, inspired by this post.