tests: Test attach uprobe to specific offset

Add a new test case test_object_uprobe_with_func_offset()
to exercise the new functionality.

Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>

Author: chenhengqi

Cargo.lock

@@ -45,6 +45,7 @@ libbpf-sys = { version = "1.4.1", default-features = false, optional = true }
 tempfile = { version = "3.3", optional = true }
 
 [dev-dependencies]
+goblin = "0.9.3"
 libbpf-rs = {path = ".", features = ["generate-test-files"]}
 libbpf-rs-dev = {path = "dev", features = ["generate-test-files"]}
 log = "0.4.4"

libbpf-rs/Cargo.toml

@@ -1,5 +1,10 @@
+use std::error::Error;
+use std::fs;
+use std::path::Path;
 use std::path::PathBuf;
 
+use goblin::elf::sym;
+use goblin::elf::Elf;
 use libbpf_rs::Map;
 use libbpf_rs::MapCore;
 use libbpf_rs::MapMut;
@@ -85,3 +90,42 @@ where
 
     value
 }
+
+pub fn get_symbol_offset(binary_path: &Path, symbol_name: &str) -> Result<usize, Box<dyn Error>> {
+    let buffer = fs::read(binary_path)?;
+    let elf = Elf::parse(&buffer)?;
+
+    // Check dynamic symbols
+    for sym in elf.dynsyms.iter() {
+        if sym.st_type() != sym::STT_FUNC {
+            continue;
+        }
+        if let Some(name) = elf.dynstrtab.get_at(sym.st_name) {
+            if name == symbol_name {
+                let sec = &elf.section_headers[sym.st_shndx];
+                let offset = sym.st_value - sec.sh_addr + sec.sh_offset;
+                return Ok(offset as usize);
+            }
+        }
+    }
+
+    // Check regular symbols
+    for sym in elf.syms.iter() {
+        if sym.st_type() != sym::STT_FUNC {
+            continue;
+        }
+        if let Some(name) = elf.strtab.get_at(sym.st_name) {
+            if name == symbol_name {
+                let sec = &elf.section_headers[sym.st_shndx];
+                let offset = sym.st_value - sec.sh_addr + sec.sh_offset;
+                return Ok(offset as usize);
+            }
+        }
+    }
+
+    Err(format!(
+        "Symbol `{}` not found in binary {:?}",
+        symbol_name, binary_path
+    )
+    .into())
+}

libbpf-rs/tests/common/mod.rs

@@ -53,6 +53,7 @@ use test_tag::tag;
 use crate::common::get_map;
 use crate::common::get_map_mut;
 use crate::common::get_prog_mut;
+use crate::common::get_symbol_offset;
 use crate::common::get_test_object;
 use crate::common::get_test_object_path;
 use crate::common::open_test_object;
@@ -1700,6 +1701,28 @@ fn test_object_uprobe_with_opts() {
     assert_eq!(result, 1);
 }
 
+#[tag(root)]
+#[test]
+fn test_object_uprobe_with_func_offset() {
+    let mut obj = get_test_object("uprobe.bpf.o");
+    let prog = get_prog_mut(&mut obj, "handle__uprobe");
+
+    let pid = unsafe { libc::getpid() };
+    let path = current_exe().expect("failed to find executable name");
+    let func_offset = get_symbol_offset(&path, "uprobe_target").unwrap();
+    let _link = prog
+        .attach_uprobe_with_opts(pid, path, func_offset, Default::default())
+        .expect("failed to attach prog");
+
+    let map = get_map_mut(&mut obj, "ringbuf");
+    let action = || {
+        let _ = uprobe_target();
+    };
+    let result = with_ringbuffer(&map, action);
+
+    assert_eq!(result, 1);
+}
+
 /// Check that we can attach a BPF program to a uprobe and access the cookie
 /// provided during attach.
 #[tag(root)]