aya parse btf type fail

[Sherlock-Holo]

consider aya still doesn't have SkStore map, so I have to create my SkStore type

#[repr(C)]
pub struct SkStore<V> {
    r#type: *const [c_int; BPF_MAP_TYPE_SK_STORAGE as _],
    map_flags: *const [c_int; BPF_F_NO_PREALLOC as _],
    key: *const c_int,
    value: *const V,
    max_entries: *const [c_int; 0],
}

unsafe impl<V: Sync> Sync for SkStore<V> {}

#[link_section = ".maps"]
#[export_name = "CONNECT_DST_IPV4_ADDR_STORAGE"]
pub static CONNECT_DST_IPV4_ADDR_STORAGE: SyncUnsafeCell<SkStore<Ipv4Addr>> =
    SyncUnsafeCell::new(SkStore {
        r#type: ptr::null(),
        map_flags: ptr::null(),
        key: ptr::null(),
        value: ptr::null(),
        max_entries: ptr::null(),
    });

however, it will fail when EbpfLoader try to load the ebpf file with error

called `Result::unwrap()` on an `Err` value: ParseError(BtfError(UnexpectedBtfType { type_id: 23 }))

unless I use

#[link_section = ".maps"]
#[export_name = "CONNECT_DST_IPV4_ADDR_STORAGE"]
pub static mut CONNECT_DST_IPV4_ADDR_STORAGE: SkStore<Ipv4Addr> = SkStore {
    r#type: ptr::null(),
    map_flags: ptr::null(),
    key: ptr::null(),
    value: ptr::null(),
    max_entries: ptr::null(),
};

to create this global static variable directly

I am not sure which one cause this problem, rustc, bpf-linker or aya crate?

[vadorovsky]

It's LLVM bug (llvm/llvm-project#143361), which I fixed here: llvm/llvm-project#144097

Basically the problem is that before my fix, LLVM wasn't looking recursively inside map types in case they are wrapped in some other types (like UnsafeCell) and therefore wasn't visiting structs used as keys or values of the map.

If you want to unblock yourself now and don't mind building LLVM from source, you could compile LLVM from this branch (the fix cherry-picked on top of LLVM 20, used by Rust nightly):

https://github.com/aya-rs/llvm-project/tree/rustc/20.1-2025-02-13

After cloning the repo and checking out the branch, you can build LLVM with:

cmake -S llvm -B build -G Ninja -DCMAKE_BUILD_TYPE=RelWithDebInfo -DLLVM_ENABLE_ASSERTIONS=ON -DLLVM_ENABLE_PROJECTS= -DLLVM_ENABLE_RUNTIMES= -DLLVM_TARGETS_TO_BUILD=BPF
cmake --build build

Then you need to build bpf-linker from source, making sure it picks up that custom LLVM build, by passing LLVM_SYS_201_PREFIX (pointing to the build/ directory in your LLVM repo clone) and --no-default-features (to make sure that your system LLVM isn't picked up):

LLVM_SYS_201_PREFIX="<path_to_your_llvm_repo>/build" cargo install --git https://github.com/aya-rs/bpf-linker --no-default-features

I'm still figuring out how to ship this fix to users, but most likely I will try to wrap up the PR for making statically linked binaries of bpf-linker in CI - aya-rs/bpf-linker#215. Can't promise when it will be done - I'm still fighting with some stuff and my schedule this week is crazy. But I will try to do it in a timely manner.

Once that's done, I will proceed with my PR adding a proper abstraction for BTF maps in Aya - #1117

[Sherlock-Holo]

I tried use https://github.com/aya-rs/llvm-project/tree/rustc/20.1-2025-02-13 this branch to build a llvm and build bpf-linker with LLVM_SYS_201_PREFIX="$PWD/build" cargo install --git https://github.com/aya-rs/bpf-linker --no-default-features, alsow before I build these, I have run cargo clean

however it still report error ParseError(BtfError(UnexpectedBtfType { type_id: 23 }))

[Sherlock-Holo]

also I have specified this

[build]
target = "bpfel-unknown-none"

[unstable]
build-std = ["core"]

[target.bpfel-unknown-none]
rustflags = ["-C", "debuginfo=2", "-C", "link-arg=--btf"]

[Sherlock-Holo]

it seems I also need this branch #1117 to load ebpf file