tests: explain libbpf env variable

test/integration-test/src/tests/relocations.rs

@@ -14,7 +14,7 @@ fn relocate_field() {
               __u8 b;
               __u8 c;
               __u8 d;
-            } __attribute__((preserve_access_index));
+            };
         "#,
         target_btf: r#"
             struct foo {
@@ -141,6 +141,8 @@ impl RelocationTest {
         Command::new("clang")
             .current_dir(tmp_dir.path())
             .args(["-c", "-g", "-O2", "-target", "bpf"])
+            // NOTE: these tests depend on libbpf, LIBBPF_INCLUDE must point its headers.
+            // This is set automatically by the integration-test xtask.
             .args([
                 "-I",
                 &std::env::var("LIBBPF_INCLUDE").context("LIBBPF_INCLUDE not set")?,

xtask/src/build_ebpf.rs

@@ -103,7 +103,12 @@ fn build_c_ebpf(opts: &BuildEbpfOptions) -> anyhow::Result<()> {
 
     let include_path = out_path.join("include");
     get_libbpf_headers(&opts.libbpf_dir, &include_path)?;
+    // Export libbpf location as an env variable since it's needed for building
+    // the relocation tests at test/integration-test/src/tests/relocations.rs
+    // We decided to make an exception and build its eBPF programs at run-time
+    // because of the many different permutations.
     std::env::set_var("LIBBPF_INCLUDE", &include_path);
+
     let files = fs::read_dir(&src).unwrap();
     for file in files {
         let p = file.unwrap().path();