Crate dynamic_loader_cache

Reader of the dynamic loader shared libraries cache

On certain operating systems, the component that loads an executable and prepares it for execution needs to resolve the shared libraries (also known as dynamically-linked libraries) that the executable depends on. These dependencies are usually only-partly specified in the executable file. The mapping from the partially-specified library to the full path of the library can be an expensive operation, so caches are usually maintained in order to speed up the mapping.

This crate gives read-only access to these caches, allowing resolution of a partially-specified library name to a full path of the library file. For example, querying the library name libc.so.6 may return a list of likely library paths:

• /usr/lib/x86_64-linux-gnu/libc.so.6
• /usr/lib/i386-linux-gnu/libc.so.6

use dynamic_loader_cache::{Cache, Result};

fn main() -> Result<()> {
    let cache = Cache::load()?;
    let libc_iter = cache
        .iter()?
        // Ignore entries with errors.
        .filter_map(Result::ok)
        // Select entries for "libc.so.6".
        .filter_map(|entry| (*entry.file_name == *"libc.so.6").then_some(entry.full_path));

    for full_path in libc_iter {
        println!("{}", full_path.display());
    }
    Ok(())
}

The crate presents a simple interface, but extracts and aggregates information from all the caches supported and present on the system. Here is an example that uses this interface:

use dynamic_loader_cache::{Cache, Result};

fn main() -> Result<()> {
    let cache = Cache::load()?;

    for entry in cache.iter()? {
        let entry = entry?;
        println!("{} => {}", entry.file_name.to_str().unwrap(), entry.full_path.display());
    }
    Ok(())
}

This crate also allows loading of a specific dynamic loader cache, instead of automatic discovery and aggregation of all supported and present caches. In order to do that, checkout the following structures: glibc_ld_so_cache_1dot1::Cache, ld_elf_so_hints::Cache, ld_so_1dot7::Cache, ld_so_hints::Cache.

Supported operating systems

The following operating systems are currently supported:

• FreeBSD: dynamic loader cache files /var/run/ld-elf.so.hints and /var/run/ld-elf32.so.hints.
• GNU/Linux: dynamic loader cache file /etc/ld.so.cache, in ld.so-1.7.0 or glibc-ld.so.cache1.1 formats, in little-endian or big-endian byte orders.
• OpenBSD/NetBSD: dynamic loader cache file /var/run/ld.so.hints.

Versioning

This project adheres to Semantic Versioning. The CHANGELOG.md file details notable changes over time.

Modules

• glibc_ld_so_cache_1dot1
  Cache of the GNU/Linux dynamic loader.
• ld_elf_so_hints
  Cache of the FreeBSD dynamic loader.
• ld_so_1dot7
  Cache of the GNU/Linux old dynamic loader.
• ld_so_hints
  Cache of the OpenBSD or NetBSD dynamic loader.

Structs

• Cache
  Reader of the dynamic loader shared libraries cache.
• Entry
  Cache entry.

Enums

• Error
  Information about a failure of an operation.

Type Aliases

• Result
  Result of a fallible operation.