utils: add an elf module and an helper to read a .BTF section from an…

… ELF file

This helpers is useful to extract .BTF ELF sections from kernel
binaries, e.g. vmlinux and .ko files.

Signed-off-by: Antoine Tenart <[email protected]>

.cirrus.yml

@@ -14,7 +14,7 @@ test_task:
     - rustup component add rustfmt
     - rustup component add clippy
   build_script: cargo build --verbose
-  test_script: cargo test --verbose
+  test_script: cargo test --verbose -F elf
   check_script:
     - cargo fmt --check
     - cargo clippy -- -D warnings

Cargo.toml

@@ -18,9 +18,11 @@ maintenance = { status = "actively-developed" }
 [dependencies]
 anyhow = "1.0"
 byteorder = "1.5"
+elf = { version = "0.7", optional = true }
 
 [dev-dependencies]
 test-case = "3.2"
 
 [features]
+elf = ["dep:elf"]
 test_runtime = []

src/lib.rs

@@ -97,6 +97,8 @@
 //!
 //! ### Feature flags
 //!
+//! - elf: Enable helpers parsing the .BTF section of ELF files in
+//!   `utils::elf`.
 //! - test_runtime: Use the system's runtime BTF files to perform extra
 //!   integration tests.
 

src/utils/elf.rs

@@ -0,0 +1,30 @@
+use std::{
+    fs::{self, File},
+    path::Path,
+};
+
+use anyhow::{anyhow, bail, Result};
+use elf::{endian::AnyEndian, ElfStream};
+
+/// Extract raw BTF data from the .BTF elf section of the given file. Output can
+/// be used to fed `from_bytes` constructors in this library.
+pub fn extract_btf_from_file<P: AsRef<Path>>(path: P) -> Result<Vec<u8>> {
+    let file = File::open(&path)
+        .map_err(|e| anyhow!("Could not open {}: {e}", path.as_ref().display()))?;
+    let mut elf = ElfStream::<AnyEndian, _>::open_stream(file)?;
+
+    let btf_hdr = match elf.section_header_by_name(".BTF")? {
+        Some(hdr) => *hdr,
+        None => bail!("No BTF section in {}", path.as_ref().display()),
+    };
+
+    let (btf, chdr) = elf.section_data(&btf_hdr)?;
+    if chdr.is_some() {
+        bail!(
+            "Compressed BTF sections are not supported ({})",
+            path.as_ref().display()
+        );
+    }
+
+    Ok(btf.to_vec())
+}

src/utils/mod.rs

@@ -2,3 +2,5 @@
 //! use cases.
 
 pub mod collection;
+#[cfg(feature = "elf")]
+pub mod elf;