ldshim

This is a simple shim for avoiding the system's global dynamic linker (e.g., /lib64/ld-linux-x86-64.so.2) to maintain path agonism.

Why?

Packaging dynamically linked binaries that are fully path agonistic requires that we override paths to avoid system-wide paths.

For shared libraries, this can be done by defining the ELF rpath to a relative path using $ORIGIN. For example: if rpath = $ORIGIN/../lib, the dynamic linker will look for binaries at <location of binary>/../lib/. This allows for bundling dynamically linked libraries in a package.

However, the dynamic linker path is placed in the .interp section of the ELF header. This value must be an absolute path, so we cannot use the technique used for shared libraries! This problem is addressed with ldshim, which manually invokes the dynamic linker from a relative path (../lib/ld-linux-x86-64.so.2), preventing the system from using the ELF-specified dynamic linker.

Building

Use make to build with GCC. This will create a static ldshim binary.

Usage

1. Determine a binary that you want to shim, for example bin/bash
2. Move the actual, dynamically linked binary to dynbin/bash
3. Place a copy of ldshim at bin/bash
4. Place a dynamic linker at lib/ld-linux-x86-64.so.2
5. Running the ldshim at bin/bash will invoke dynbin/bash using the dynamic linker at lib/ld-linux-x86-64.so.2

License

SPDX-License-Identifier: Apache-2.0 OR MIT