btf: add integration tests for relocations

Add new integrations tests for BTF relocations.

test/integration-test/Cargo.toml

@@ -18,3 +18,4 @@ log = "0.4"
 object = { version = "0.30", default-features = false, features = ["std", "read_core", "elf"] }
 rbpf = "0.1.0"
 regex = "1"
+tempfile = "3.3.0"

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

@@ -7,6 +7,7 @@ use std::{ffi::CStr, mem};
 pub mod elf;
 pub mod load;
 pub mod rbpf;
+pub mod relocations;
 pub mod smoke;
 
 pub use integration_test_macros::integration_test;

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

@@ -0,0 +1,226 @@
+use anyhow::{Context, Result};
+use std::{process::Command, thread::sleep, time::Duration};
+
+use aya::{maps::Array, programs::TracePoint, BpfLoader, Btf, Endianness};
+
+use super::{integration_test, IntegrationTest};
+
+#[integration_test]
+fn relocate_field() {
+    let test = RelocationTest {
+        local_definition: r#"
+            struct foo {
+              __u8 a;
+              __u8 b;
+              __u8 c;
+              __u8 d;
+            } __attribute__((preserve_access_index));
+        "#,
+        target_btf: r#"
+            struct foo {
+              __u8 a;
+              __u8 c;
+              __u8 b;
+              __u8 d;
+            } s1;
+        "#,
+        relocation_code: r#"
+            __u8 memory[] = {1, 2, 3, 4};
+            __u32 value = BPF_CORE_READ((struct foo *)&memory, c);
+        "#,
+    }
+    .build()
+    .unwrap();
+    assert_eq!(test.run().unwrap(), 2);
+    assert_eq!(test.run_no_btf().unwrap(), 3);
+}
+
+#[integration_test]
+fn relocate_enum() {
+    let test = RelocationTest {
+        local_definition: r#"
+            enum foo { D = 1 };
+        "#,
+        target_btf: r#"
+            enum foo { D = 4 } e1;
+        "#,
+        relocation_code: r#"
+            __u32 value = bpf_core_enum_value(enum foo, D);
+        "#,
+    }
+    .build()
+    .unwrap();
+    assert_eq!(test.run().unwrap(), 4);
+    assert_eq!(test.run_no_btf().unwrap(), 0);
+}
+
+/// Utility code for running relocation tests:
+/// - Generates the eBPF program using probided local definition and relocation code
+/// - Generates the BTF from the target btf code
+struct RelocationTest {
+    /// Data structure definition, local to the eBPF program and embedded in the eBPF bytecode
+    local_definition: &'static str,
+    /// Target data structure definition. What the vmlinux would actually contain.
+    target_btf: &'static str,
+    /// Code executed by the eBPF program to test the relocation.
+    /// The format should be:
+    // __u8 memory[] = { ... };
+    // __u32 value = BPF_CORE_READ((struct foo *)&memory, ...);
+    //
+    // The generated code will be executed by attaching a tracepoint to sched_switch
+    // and emitting `__u32 value` an a map. See the code template below for more details.
+    relocation_code: &'static str,
+}
+
+impl RelocationTest {
+    /// Build a RelocationTestRunner
+    fn build(&self) -> Result<RelocationTestRunner> {
+        Ok(RelocationTestRunner {
+            ebpf: self.build_ebpf()?,
+            btf: self.build_btf()?,
+        })
+    }
+
+    /// - Generate the source eBPF filling a template
+    /// - Compile it with clang
+    fn build_ebpf(&self) -> Result<Vec<u8>> {
+        let local_definition = self.local_definition;
+        let relocation_code = self.relocation_code;
+        let tmp_dir = tempfile::tempdir().context("Error making temp dir")?;
+        let ebpf_file = tmp_dir.path().join("ebpf_program.c");
+        std::fs::write(
+            &ebpf_file,
+            format!(
+                r#"
+                    #include <linux/bpf.h>
+
+                    #include <bpf/bpf_core_read.h>
+                    #include <bpf/bpf_helpers.h>
+                    #include <bpf/bpf_tracing.h>
+
+                    {local_definition}
+
+                    struct {{
+                      __uint(type, BPF_MAP_TYPE_ARRAY);
+                      __type(key, __u32);
+                      __type(value, __u32);
+                      __uint(max_entries, 1);
+                    }} output_map SEC(".maps");
+
+                    SEC("tracepoint/bpf_prog") int bpf_prog(void *ctx) {{
+                      __u32 key = 0;
+                      {relocation_code}
+                      bpf_map_update_elem(&output_map, &key, &value, BPF_ANY);
+                      return 0;
+                    }}
+
+                    char _license[] SEC("license") = "GPL";
+                "#
+            ),
+        )
+        .context("Writing bpf program failed")?;
+        Command::new("clang")
+            .current_dir(tmp_dir.path())
+            .args(["-c", "-g", "-O2", "-target", "bpf"])
+            .args([
+                "-I",
+                &std::env::var("LIBBPF_INCLUDE").context("LIBBPF_INCLUDE not set")?,
+            ])
+            .arg(&ebpf_file)
+            .status()
+            .context("Failed to run clang")?
+            .success()
+            .then_some(())
+            .context("Failed to compile eBPF program")?;
+        let ebpf = std::fs::read(ebpf_file.with_extension("o"))
+            .context("Error reading compiled eBPF program")?;
+        Ok(ebpf)
+    }
+
+    /// - Generate the target BTF source with a mock main()
+    /// - Compile it with clang
+    /// - Extract the BTF with pahole
+    fn build_btf(&self) -> Result<Btf> {
+        let target_btf = self.target_btf;
+        let tmp_dir = tempfile::tempdir().context("Error making temp dir")?;
+        // BTF files can be generated and inspected with these commands:
+        // $ clang -c -g -O2 -target bpf target.c
+        // $ pahole --btf_encode_detached=target.btf -V target.o
+        // $ bpftool btf dump file ./target.btf  format c
+        let btf_file = tmp_dir.path().join("target_btf.c");
+        std::fs::write(
+            &btf_file,
+            format!(
+                r#"
+                    #include <linux/types.h>
+                    {target_btf}
+                    int main() {{ return 0; }}
+                "#
+            ),
+        )
+        .context("Writing bpf program failed")?;
+        Command::new("clang")
+            .current_dir(tmp_dir.path())
+            .args(["-c", "-g", "-O2", "-target", "bpf"])
+            .arg(&btf_file)
+            .status()
+            .context("Failed to run clang")?
+            .success()
+            .then_some(())
+            .context("Failed to compile BTF")?;
+        Command::new("pahole")
+            .current_dir(tmp_dir.path())
+            .arg("--btf_encode_detached=target.btf")
+            .arg(btf_file.with_extension("o"))
+            .status()
+            .context("Failed to run pahole")?
+            .success()
+            .then_some(())
+            .context("Failed to extract BTF")?;
+        let btf = Btf::parse_file(tmp_dir.path().join("target.btf"), Endianness::default())
+            .context("Error parsing generated BTF")?;
+        Ok(btf)
+    }
+}
+
+struct RelocationTestRunner {
+    ebpf: Vec<u8>,
+    btf: Btf,
+}
+
+impl RelocationTestRunner {
+    /// Run test and return the output value
+    fn run(&self) -> Result<u32> {
+        self.run_internal(true)
+    }
+
+    /// Run without loading btf
+    fn run_no_btf(&self) -> Result<u32> {
+        self.run_internal(false)
+    }
+
+    fn run_internal(&self, with_relocations: bool) -> Result<u32> {
+        let mut loader = BpfLoader::new();
+        if with_relocations {
+            loader.btf(Some(&self.btf));
+        }
+        let mut bpf = loader.load(&self.ebpf).context("Loading eBPF failed")?;
+        let program: &mut TracePoint = bpf
+            .program_mut("bpf_prog")
+            .context("bpf_prog not found")?
+            .try_into()
+            .context("program not a tracepoint")?;
+        program.load().context("Loading tracepoint failed")?;
+        // Attach to sched_switch and wait some time to make sure it executed at least once
+        program
+            .attach("sched", "sched_switch")
+            .context("attach failed")?;
+        sleep(Duration::from_millis(1000));
+        // To inspect the loaded eBPF bytecode, increse the timeout and run:
+        // $ sudo bpftool prog dump xlated name bpf_prog
+
+        let output_map: Array<_, u32> = bpf.take_map("output_map").unwrap().try_into().unwrap();
+        let key = 0;
+        output_map.get(&key, 0).context("Getting key 0 failed")
+    }
+}

xtask/src/build_ebpf.rs

@@ -103,6 +103,7 @@ fn build_c_ebpf(opts: &BuildEbpfOptions) -> anyhow::Result<()> {
 
     let include_path = out_path.join("include");
     get_libbpf_headers(&opts.libbpf_dir, &include_path)?;
+    std::env::set_var("LIBBPF_INCLUDE", &include_path);
     let files = fs::read_dir(&src).unwrap();
     for file in files {
         let p = file.unwrap().path();