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// Copyright (c) Meta Platforms, Inc. and affiliates.
//
// This software may be used and distributed according to the terms of the
// GNU General Public License version 2.
use anyhow::anyhow;
use anyhow::bail;
use anyhow::Context;
use anyhow::Result;
use glob::glob;
use libbpf_cargo::SkeletonBuilder;
use sscanf::sscanf;
use std::collections::BTreeSet;
use std::collections::HashMap;
use std::env;
use std::path::Path;
use std::path::PathBuf;
use std::process::Command;
lazy_static::lazy_static! {
// Map clang archs to the __TARGET_ARCH list in
// tools/lib/bpf/bpf_tracing.h in the kernel tree.
static ref ARCH_MAP: HashMap<&'static str, &'static str> = vec![
("x86", "x86"),
("x86_64", "x86"),
("s390", "s390"),
("s390x", "s390"),
("arm", "arm"),
("aarch64", "arm64"),
("mips", "mips"),
("mips64", "mips"),
("ppc32", "powerpc"),
("ppc64", "powerpc"),
("ppc64le", "powerpc"),
("sparc", "sparc"),
("sparcv9", "sparc"),
("riscv32", "riscv"),
("riscv64", "riscv"),
("arc", "arc"), // unsure this is supported
("loongarch64", "loongarch"), // ditto
].into_iter().collect();
}
#[derive(Debug)]
/// # Build helpers for sched_ext schedulers with Rust userspace component
///
/// This is to be used from `build.rs` of a cargo project which implements a
/// [sched_ext](https://github.com/sched-ext/scx) scheduler with C BPF
/// component and Rust userspace component. `BpfBuilder` provides everything
/// necessary to build the BPF component and generate Rust bindings.
/// BpfBuilder provides the followings.
///
/// 1. *`vmlinux.h` and other common BPF header files*
///
/// All sched_ext BPF implementations require `vmlinux.h` and many make use
/// of common constructs such as
/// [`user_exit_info`](https://github.com/sched-ext/scx/blob/main/scheds/include/common/user_exit_info.h).
/// `BpfBuilder` makes these headers available when compiling BPF source
/// code and generating bindings for it. The included headers can be browsed
/// at <https://github.com/sched-ext/scx/tree/main/scheds/include>.
///
/// These headers can be superseded using environment variables which will
/// be discussed later.
///
/// 2. *Header bindings using `bindgen`*
///
/// If enabled with `.enable_intf()`, the input `.h` file is processed by
/// `bindgen` to generate Rust bindings. This is useful in establishing
/// shared constants and data types between the BPF and user components.
///
/// Note that the types generated with `bindgen` are different from the
/// types used by the BPF skeleton even when they are the same types in BPF.
/// This is a source of ugliness and we are hoping to address it by
/// improving `libbpf-cargo` in the future.
///
/// 3. *BPF compilation and generation of the skeleton and its bindings*
///
/// If enabled with `.enable_skel()`, the input `.bpf.c` file is compiled
/// and its skeleton and bindings are generated using `libbpf-cargo`.
///
/// ## An Example
///
/// This section shows how `BpfBuilder` can be used in an example project.
/// For a concrete example, take a look at
/// [`scx_rusty`](https://github.com/sched-ext/scx/tree/main/scheds/rust/scx_rusty).
///
/// A minimal source tree using all features would look like the following:
///
/// ```text
/// scx_hello_world
/// |-- Cargo.toml
/// |-- build.rs
/// \-- src
/// |-- main.rs
/// |-- bpf_intf.rs
/// |-- bpf_skel.rs
/// \-- bpf
/// |-- intf.h
/// \-- main.c
/// ```
///
/// The following three files would contain the actual implementation:
///
/// - `src/main.rs`: Rust userspace component which loads the BPF blob and
/// interacts it using the generated bindings.
///
/// - `src/bpf/intf.h`: C header file definining constants and structs
/// that will be used by both the BPF and userspace components.
///
/// - `src/bpf/main.c`: C source code implementing the BPF component -
/// including `struct sched_ext_ops`.
///
/// And then there are boilerplates to generate the bindings and make them
/// available as modules to `main.rs`.
///
/// - `Cargo.toml`: Includes `scx_utils` in the `[build-dependencies]`
/// section.
///
/// - `build.rs`: Uses `scx_utils::BpfBuilder` to build and generate
/// bindings for the BPF component. For this project, it can look like the
/// following.
///
/// ```should_panic
/// fn main() {
/// scx_utils::BpfBuilder::new()
/// .unwrap()
/// .enable_intf("src/bpf/intf.h", "bpf_intf.rs")
/// .enable_skel("src/bpf/main.bpf.c", "bpf")
/// .build()
/// .unwrap();
/// }
/// ```
///
/// - `bpf_intf.rs`: Import the bindings generated by `bindgen` into a
/// module. Above, we told `.enable_intf()` to generate the bindings into
/// `bpf_intf.rs`, so the file would look like the following. The `allow`
/// directives are useful if the header is including `vmlinux.h`.
///
/// ```ignore
/// #![allow(non_upper_case_globals)]
/// #![allow(non_camel_case_types)]
/// #![allow(non_snake_case)]
/// #![allow(dead_code)]
///
/// include!(concat!(env!("OUT_DIR"), "/bpf_intf.rs"));
/// ```
///
/// - `bpf_skel.rs`: Import the BPF skeleton bindings generated by
/// `libbpf-cargo` into a module. Above, we told `.enable_skel()` to use the
/// skeleton name `bpf`, so the file would look like the following.
///
/// ```ignore
/// include!(concat!(env!("OUT_DIR"), "/bpf_skel.rs"));
/// ```
///
/// ## Compiler Flags and Environment Variables
///
/// BPF being its own CPU architecture and independent runtime environment,
/// build environment and steps are already rather complex. The need to
/// interface between two different languages - C and Rust - adds further
/// complexities. `BpfBuilder` automates most of the process. The determined
/// build environment is recorded in the `build.rs` output and can be
/// obtained with a command like the following:
///
/// ```text
/// $ grep '^scx_utils:clang=' target/release/build/scx_rusty-*/output
/// ```
///
/// While the automatic settings should work most of the time, there can be
/// times when overriding them is necessary. The following environment
/// variables can be used to customize the build environment.
///
/// - `BPF_CLANG`: The clang command to use. (Default: `clang`)
///
/// - `BPF_CFLAGS`: Compiler flags to use when building BPF source code. If
/// specified, the flags from this variable are the only flags passed to
/// the compiler. `BpfBuilder` won't generate any flags including `-I`
/// flags for the common header files and other `CFLAGS` related variables
/// are ignored.
///
/// - `BPF_BASE_CFLAGS`: Override the non-include part of cflags.
///
/// - `BPF_EXTRA_CFLAGS_PRE_INCL`: Add cflags before the automic include
/// search path options. Header files in the search paths added by this
/// variable will supercede the automatic ones.
///
/// - `BPF_EXTRA_CFLAGS_POST_INCL`: Add cflags after the automic include
/// search path options. Header paths added by this variable will be
/// searched only if the target header file can't be found in the
/// automatic header paths.
///
/// - `RUSTFLAGS`: This is a generic `cargo` flag and can be useful for
/// specifying extra linker flags.
///
/// A common case for using the above flags is using the latest `libbpf`
/// from the kernel tree. Let's say the kernel tree is at `$KERNEL` and
/// `libbpf`. The following builds `libbpf` shipped with the kernel:
///
/// ```test
/// $ cd $KERNEL
/// $ make -C tools/bpf/bpftool
/// ```
///
/// To link the scheduler against the resulting `libbpf`:
///
/// ```test
/// $ env BPF_EXTRA_CFLAGS_POST_INCL=$KERNEL/tools/bpf/bpftool/libbpf/include \
/// RUSTFLAGS="-C link-args=-lelf -C link-args=-lz -C link-args=-lzstd \
/// -L$KERNEL/tools/bpf/bpftool/libbpf" cargo build --release
/// ```
pub struct BpfBuilder {
clang: (String, String, String), // (clang, ver, arch)
cflags: Vec<String>,
out_dir: PathBuf,
intf_input_output: Option<(String, String)>,
skel_input_name: Option<(String, String)>,
skel_deps: Option<Vec<String>>,
}
impl BpfBuilder {
fn skip_clang_version_prefix(line: &str) -> &str {
if let Some(index) = line.find("clang version") {
&line[index..]
} else {
line
}
}
fn find_clang() -> Result<(String, String, String)> {
let clang = env::var("BPF_CLANG").unwrap_or("clang".into());
let output = Command::new(&clang)
.args(["--version"])
.output()
.with_context(|| format!("Failed to run \"{} --version\"", &clang))?;
let stdout = String::from_utf8(output.stdout)?;
let (mut ver, mut arch) = (None, None);
for line in stdout.lines() {
if let Ok(v) = sscanf!(
Self::skip_clang_version_prefix(line),
"clang version {String}"
) {
// Version could be followed by (URL SHA1). Only take
// the first word.
ver = Some(v.split_whitespace().next().unwrap().to_string());
continue;
}
if let Ok(v) = sscanf!(line, "Target: {String}") {
arch = Some(v.split('-').next().unwrap().to_string());
continue;
}
}
let (ver, arch) = (
ver.ok_or(anyhow!("Failed to read clang version"))?,
arch.ok_or(anyhow!("Failed to read clang target arch"))?,
);
if version_compare::compare(&ver, "16") == Ok(version_compare::Cmp::Lt) {
bail!(
"clang < 16 loses high 32 bits of 64 bit enums when compiling BPF ({:?} ver={:?})",
&clang,
&ver
);
}
if version_compare::compare(&ver, "17") == Ok(version_compare::Cmp::Lt) {
println!(
"cargo:warning=clang >= 17 recommended ({:?} ver={:?})",
&clang, &ver
);
}
Ok((clang, ver, arch))
}
fn determine_base_cflags(
(clang, _ver, arch): &(String, String, String),
) -> Result<Vec<String>> {
// Determine kernel target arch.
let kernel_target = match ARCH_MAP.get(arch.as_str()) {
Some(v) => v,
None => bail!("CPU arch {:?} not found in ARCH_MAP", &arch),
};
// Determine system includes.
let output = Command::new(&clang)
.args(["-v", "-E", "-"])
.output()
.with_context(|| format!("Failed to run \"{} -v -E - < /dev/null", &clang))?;
let stderr = String::from_utf8(output.stderr)?;
let mut sys_incls = None;
for line in stderr.lines() {
if line == "#include <...> search starts here:" {
sys_incls = Some(vec![]);
continue;
}
if sys_incls.is_none() {
continue;
}
if line == "End of search list." {
break;
}
sys_incls.as_mut().unwrap().push(line.trim());
}
let sys_incls = match sys_incls {
Some(v) => v,
None => bail!("Failed to find system includes from {:?}", &clang),
};
// Determine endian.
let output = Command::new(&clang)
.args(["-dM", "-E", "-"])
.output()
.with_context(|| format!("Failed to run \"{} -dM E - < /dev/null", &clang))?;
let stdout = String::from_utf8(output.stdout)?;
let mut endian = None;
for line in stdout.lines() {
match sscanf!(line, "#define __BYTE_ORDER__ {str}") {
Ok(v) => {
endian = Some(match v {
"__ORDER_LITTLE_ENDIAN__" => "little",
"__ORDER_BIG_ENDIAN__" => "big",
v => bail!("Unknown __BYTE_ORDER__ {:?}", v),
});
break;
}
_ => {}
}
}
let endian = match endian {
Some(v) => v,
None => bail!("Failed to find __BYTE_ORDER__ from {:?}", &clang),
};
// Assemble cflags.
let mut cflags: Vec<String> =
["-g", "-O2", "-Wall", "-Wno-compare-distinct-pointer-types'"]
.into_iter()
.map(|x| x.into())
.collect();
cflags.push(format!("-D__TARGET_ARCH_{}", &kernel_target));
cflags.push("-mcpu=v3".into());
cflags.push(format!("-m{}-endian", endian));
cflags.append(
&mut sys_incls
.into_iter()
.flat_map(|x| ["-idirafter".into(), x.into()])
.collect(),
);
Ok(cflags)
}
const BPF_H_TAR: &'static [u8] = include_bytes!(concat!(env!("OUT_DIR"), "/bpf_h.tar"));
fn install_bpf_h<P: AsRef<Path>>(dest: P) -> Result<()> {
let mut ar = tar::Archive::new(Self::BPF_H_TAR);
ar.unpack(dest)?;
Ok(())
}
/// Return `(VER, SHA1)` from which the bulit-in `vmlinux.h` is generated.
pub fn vmlinux_h_ver_sha1() -> (String, String) {
let mut ar = tar::Archive::new(Self::BPF_H_TAR);
for file in ar.entries().unwrap() {
let file = file.unwrap();
if file.header().path().unwrap() != Path::new("vmlinux/vmlinux.h") {
continue;
}
let name = file
.link_name()
.unwrap()
.unwrap()
.to_string_lossy()
.to_string();
return sscanf!(name, "vmlinux-v{String}-g{String}.h").unwrap();
}
panic!("vmlinux/vmlinux.h not found");
}
fn determine_cflags<P>(clang: &(String, String, String), out_dir: P) -> Result<Vec<String>>
where
P: AsRef<Path> + std::fmt::Debug,
{
let bpf_h = out_dir
.as_ref()
.join("scx_utils-bpf_h")
.to_str()
.ok_or(anyhow!(
"{:?}/scx_utils-bph_h can't be converted to str",
&out_dir
))?
.to_string();
Self::install_bpf_h(&bpf_h)?;
let mut cflags = Vec::<String>::new();
cflags.append(&mut match env::var("BPF_BASE_CFLAGS") {
Ok(v) => v.split_whitespace().map(|x| x.into()).collect(),
_ => Self::determine_base_cflags(&clang)?,
});
cflags.append(&mut match env::var("BPF_EXTRA_CFLAGS_PRE_INCL") {
Ok(v) => v.split_whitespace().map(|x| x.into()).collect(),
_ => vec![],
});
cflags.push(format!("-I{}", &bpf_h));
cflags.push(format!("-I{}/vmlinux", &bpf_h));
cflags.push(format!("-I{}/bpf-compat", &bpf_h));
cflags.append(&mut match env::var("BPF_EXTRA_CFLAGS_POST_INCL") {
Ok(v) => v.split_whitespace().map(|x| x.into()).collect(),
_ => vec![],
});
Ok(cflags)
}
/// Create a new `BpfBuilder` struct. Call `enable` and `set` methods to
/// configure and `build` method to compile and generate bindings. See
/// the struct documentation for details.
pub fn new() -> Result<Self> {
let out_dir = PathBuf::from(env::var("OUT_DIR")?);
let clang = Self::find_clang()?;
let cflags = match env::var("BPF_CFLAGS") {
Ok(v) => v.split_whitespace().map(|x| x.into()).collect(),
_ => Self::determine_cflags(&clang, &out_dir)?,
};
println!("scx_utils:clang={:?} {:?}", &clang, &cflags);
Ok(Self {
clang,
cflags,
out_dir,
intf_input_output: None,
skel_input_name: None,
skel_deps: None,
})
}
/// Enable generation of header bindings using `bindgen`. `@input` is
/// the `.h` file defining the constants and types to be shared between
/// BPF and Rust components. `@output` is the `.rs` file to be
/// generated.
pub fn enable_intf(&mut self, input: &str, output: &str) -> &mut Self {
self.intf_input_output = Some((input.into(), output.into()));
self
}
/// Enable compilation of BPF code and generation of the skeleton and
/// its Rust bindings. `@input` is the `.bpf.c` file containing the BPF
/// source code and `@output` is the `.rs` file to be generated.
pub fn enable_skel(&mut self, input: &str, name: &str) -> &mut Self {
self.skel_input_name = Some((input.into(), name.into()));
self
}
/// By default, all `.[hc]` files in the same directory as the source
/// BPF `.c` file are treated as dependencies and the skeleton is
/// regenerated if any has changed. This method replaces the automatic
/// dependencies with `@deps`.
pub fn set_skel_deps<'a, I>(&mut self, deps: I) -> &mut Self
where
I: IntoIterator<Item = &'a str>,
{
self.skel_deps = Some(deps.into_iter().map(|d| d.to_string()).collect());
self
}
fn bindgen_bpf_intf(&self, deps: &mut BTreeSet<String>) -> Result<()> {
let (input, output) = match &self.intf_input_output {
Some(pair) => pair,
None => return Ok(()),
};
// Tell cargo to invalidate the built crate whenever the wrapper changes
deps.insert(input.to_string());
// FIXME - bindgen's API changed between 0.68 and 0.69 so that
// `bindgen::CargoCallbacks::new()` should be used instead of
// `bindgen::CargoCallbacks`. Unfortunately, as of Dec 2023, fedora
// is shipping 0.68. To accommodate fedora, allow both 0.68 and 0.69
// of bindgen and suppress deprecation warning. Remove the following
// once fedora can be updated to bindgen >= 0.69.
#[allow(deprecated)]
// The bindgen::Builder is the main entry point to bindgen, and lets
// you build up options for the resulting bindings.
let bindings = bindgen::Builder::default()
// Should run clang with the same -I options as BPF compilation.
.clang_args(
self.cflags
.iter()
.chain(["-target".into(), "bpf".into()].iter()),
)
// The input header we would like to generate bindings for.
.header(input)
// Tell cargo to invalidate the built crate whenever any of the
// included header files changed.
.parse_callbacks(Box::new(bindgen::CargoCallbacks))
.generate()
.context("Unable to generate bindings")?;
bindings
.write_to_file(self.out_dir.join(output))
.context("Couldn't write bindings")
}
fn gen_bpf_skel(&self, deps: &mut BTreeSet<String>) -> Result<()> {
let (input, name) = match &self.skel_input_name {
Some(pair) => pair,
None => return Ok(()),
};
let obj = self.out_dir.join(format!("{}.bpf.o", name));
let skel_path = self.out_dir.join(format!("{}_skel.rs", name));
SkeletonBuilder::new()
.source(input)
.obj(&obj)
.clang(&self.clang.0)
.clang_args(&self.cflags)
.build_and_generate(&skel_path)?;
match &self.skel_deps {
Some(skel_deps) => {
for path in skel_deps {
deps.insert(path.to_string());
}
}
None => {
let c_path = PathBuf::from(input);
let dir = c_path
.parent()
.ok_or(anyhow!("Source {:?} doesn't have parent dir", c_path))?
.to_str()
.ok_or(anyhow!("Parent dir of {:?} isn't a UTF-8 string", c_path))?;
for path in glob(&format!("{}/*.[hc]", dir))?.filter_map(Result::ok) {
deps.insert(
path.to_str()
.ok_or(anyhow!("Path {:?} is not a valid string", path))?
.to_string(),
);
}
}
}
Ok(())
}
/// Build and generate the enabled bindings.
pub fn build(&self) -> Result<()> {
let mut deps = BTreeSet::new();
self.bindgen_bpf_intf(&mut deps)?;
self.gen_bpf_skel(&mut deps)?;
println!("cargo:rerun-if-env-changed=BPF_CLANG");
println!("cargo:rerun-if-env-changed=BPF_CFLAGS");
println!("cargo:rerun-if-env-changed=BPF_BASE_CFLAGS");
println!("cargo:rerun-if-env-changed=BPF_EXTRA_CFLAGS_PRE_INCL");
println!("cargo:rerun-if-env-changed=BPF_EXTRA_CFLAGS_POST_INCL");
for dep in deps.iter() {
println!("cargo:rerun-if-changed={}", dep);
}
Ok(())
}
}
#[cfg(test)]
mod tests {
#[test]
fn test_bpf_builder_new() {
let res = super::BpfBuilder::new();
assert!(res.is_ok(), "Failed to create BpfBuilder ({:?})", &res);
}
#[test]
fn test_vmlinux_h_ver_sha1() {
let (ver, sha1) = super::BpfBuilder::vmlinux_h_ver_sha1();
println!("vmlinux.h: ver={:?} sha1={:?}", &ver, &sha1,);
assert!(
regex::Regex::new(r"^[1-9][0-9]*\.[1-9][0-9]*(\.[1-9][0-9]*)?$")
.unwrap()
.is_match(&ver)
);
assert!(regex::Regex::new(r"^[0-9a-z]{12}$")
.unwrap()
.is_match(&sha1));
}
}