Add option to replace an imported symbol #416
Description
Is your feature request related to a problem? Please describe.
Using the rpath arguments (e.g. --add-rpath), patchelf can override the location of libraries. However, libraries have other ways of depending on file system paths. A common example is drivers containing a hard-coded path to firmware binaries, which the library fopen()s.
Example: Broadcom fingerprint driver, the .so contains a hardcoded path to /var/lib/fprint/fw.
Currently it is difficult to replace such paths.
Describe the solution you'd like
Add a new argument to patchelf, --replace-symbol NAME_ORIG NAME_NEW. If specified, patchelf will iterate over the symbol table (.dynsym section), and replace the symbol with the name NAME_ORIG with NAME_NEW, adding it to the .dynstr section if neccessary.
This allows one to replace the fopen call from the library with a wrapper function, which can inspect the path it receives and change it if neccessary.
Example invocation:
$ # assume that fopen_wrapper.c defines a `fopen_wrapper()` function with the same signature as `fopen()`
$ cc -fPIC -shared fopen_wrapper.c -o libfopen_wrapper.so
$ patchelf \
--replace-symbol fopen fopen_wrapper \
--add-needed libfopen_wrapper.so \
libdriver.so
Describe alternatives you've considered
- Use
buildFHSUserEnvfrom nixpkgs to give the process the filesystem layout it needs. - Use LD_PRELOAD to inject the wrapper into the process.
These methods have the disadvantage that they affect an entire process tree, not just the single library that needs patching.
Additional context
I have a prototype quality implementation of this feature. If this feature request is accepted, I'll clean it up and add tests/documentation for it.
Upstreaming of this feature has been requested by the iscan-snap project, which attempts to package scanner drivers using snap.