Initial BTF support

Still missing a couple of things but the bulk is there

scripts/gen-bindings

@@ -24,6 +24,39 @@ BPF_TYPES="\
 
 BPF_VARS="\
     BPF_PSEUDO_.*
+    BPF_ALU \
+    BPF_ALU64 \
+    BPF_LDX \
+    BPF_ST \
+    BPF_STX \
+    BPF_LD \
+    BPF_K \
+    BPF_DW \
+    BPF_W \
+    BPF_H \
+    BPF_B
+    "
+
+BTF_TYPES="\
+    btf_header \
+    btf_ext_header \
+    btf_ext_info \
+    btf_ext_info_sec \
+    bpf_core_relo \
+    bpf_core_relo_kind \
+    btf_type \
+    btf_enum \
+    btf_array \
+    btf_member \
+    btf_param \
+    btf_var \
+    btf_var_secinfo
+
+    "
+
+BTF_VARS="\
+    BTF_KIND_.*
+    BTF_INT_.*
     "
 
 PERF_TYPES="\
@@ -52,6 +85,28 @@ bindgen $LIBBPF_DIR/include/uapi/linux/bpf.h \
     done) \
     > $OUTPUT_DIR/bpf_bindings.rs
 
+bindgen $LIBBPF_DIR/include/uapi/linux/btf.h \
+    --no-layout-tests \
+    --default-enum-style moduleconsts \
+    $(for ty in $BTF_TYPES; do
+        echo --whitelist-type "$ty"
+    done) \
+    $(for var in $BTF_VARS; do
+        echo --whitelist-var "$var"
+    done) \
+    > $OUTPUT_DIR/btf_bindings.rs
+
+bindgen $LIBBPF_DIR/src/libbpf_internal.h \
+    --no-layout-tests \
+    --default-enum-style moduleconsts \
+    $(for ty in $BTF_TYPES; do
+        echo --whitelist-type "$ty"
+    done) \
+    $(for var in $BTF_VARS; do
+        echo --whitelist-var "$var"
+    done) \
+    > $OUTPUT_DIR/btf_internal_bindings.rs
+
 bindgen include/perf_wrapper.h \
     --no-layout-tests \
     --default-enum-style moduleconsts \

src/bpf.rs

@@ -9,7 +9,7 @@ use thiserror::Error;
 use crate::{
     generated::bpf_insn,
     maps::{Map, MapError},
-    obj::{relocate, Object, ParseError, RelocationError},
+    obj::{Object, ParseError, RelocationError},
     programs::{KProbe, Program, ProgramData, ProgramError, SocketFilter, TracePoint, UProbe, Xdp},
     syscalls::bpf_map_update_elem_ptr,
 };
@@ -68,7 +68,7 @@ impl Bpf {
             maps.push(map);
         }
 
-        relocate(&mut obj, maps.as_slice())?;
+        obj.relocate(maps.as_slice())?;
 
         let programs = obj
             .programs

src/generated/bpf_bindings.rs

@@ -81,6 +81,17 @@ where
         }
     }
 }
+pub const BPF_LD: u32 = 0;
+pub const BPF_LDX: u32 = 1;
+pub const BPF_ST: u32 = 2;
+pub const BPF_STX: u32 = 3;
+pub const BPF_ALU: u32 = 4;
+pub const BPF_W: u32 = 0;
+pub const BPF_H: u32 = 8;
+pub const BPF_B: u32 = 16;
+pub const BPF_K: u32 = 0;
+pub const BPF_ALU64: u32 = 7;
+pub const BPF_DW: u32 = 24;
 pub const BPF_PSEUDO_MAP_FD: u32 = 1;
 pub const BPF_PSEUDO_MAP_VALUE: u32 = 2;
 pub const BPF_PSEUDO_BTF_ID: u32 = 3;

src/generated/btf_bindings.rs

@@ -0,0 +1,90 @@
+/* automatically generated by rust-bindgen 0.55.1 */
+
+pub const BTF_KIND_UNKN: u32 = 0;
+pub const BTF_KIND_INT: u32 = 1;
+pub const BTF_KIND_PTR: u32 = 2;
+pub const BTF_KIND_ARRAY: u32 = 3;
+pub const BTF_KIND_STRUCT: u32 = 4;
+pub const BTF_KIND_UNION: u32 = 5;
+pub const BTF_KIND_ENUM: u32 = 6;
+pub const BTF_KIND_FWD: u32 = 7;
+pub const BTF_KIND_TYPEDEF: u32 = 8;
+pub const BTF_KIND_VOLATILE: u32 = 9;
+pub const BTF_KIND_CONST: u32 = 10;
+pub const BTF_KIND_RESTRICT: u32 = 11;
+pub const BTF_KIND_FUNC: u32 = 12;
+pub const BTF_KIND_FUNC_PROTO: u32 = 13;
+pub const BTF_KIND_VAR: u32 = 14;
+pub const BTF_KIND_DATASEC: u32 = 15;
+pub const BTF_KIND_MAX: u32 = 15;
+pub const BTF_INT_SIGNED: u32 = 1;
+pub const BTF_INT_CHAR: u32 = 2;
+pub const BTF_INT_BOOL: u32 = 4;
+pub type __u8 = ::std::os::raw::c_uchar;
+pub type __u16 = ::std::os::raw::c_ushort;
+pub type __s32 = ::std::os::raw::c_int;
+pub type __u32 = ::std::os::raw::c_uint;
+#[repr(C)]
+#[derive(Debug, Copy, Clone)]
+pub struct btf_header {
+    pub magic: __u16,
+    pub version: __u8,
+    pub flags: __u8,
+    pub hdr_len: __u32,
+    pub type_off: __u32,
+    pub type_len: __u32,
+    pub str_off: __u32,
+    pub str_len: __u32,
+}
+#[repr(C)]
+#[derive(Copy, Clone)]
+pub struct btf_type {
+    pub name_off: __u32,
+    pub info: __u32,
+    pub __bindgen_anon_1: btf_type__bindgen_ty_1,
+}
+#[repr(C)]
+#[derive(Copy, Clone)]
+pub union btf_type__bindgen_ty_1 {
+    pub size: __u32,
+    pub type_: __u32,
+    _bindgen_union_align: u32,
+}
+#[repr(C)]
+#[derive(Debug, Copy, Clone)]
+pub struct btf_enum {
+    pub name_off: __u32,
+    pub val: __s32,
+}
+#[repr(C)]
+#[derive(Debug, Copy, Clone)]
+pub struct btf_array {
+    pub type_: __u32,
+    pub index_type: __u32,
+    pub nelems: __u32,
+}
+#[repr(C)]
+#[derive(Debug, Copy, Clone)]
+pub struct btf_member {
+    pub name_off: __u32,
+    pub type_: __u32,
+    pub offset: __u32,
+}
+#[repr(C)]
+#[derive(Debug, Copy, Clone)]
+pub struct btf_param {
+    pub name_off: __u32,
+    pub type_: __u32,
+}
+#[repr(C)]
+#[derive(Debug, Copy, Clone)]
+pub struct btf_var {
+    pub linkage: __u32,
+}
+#[repr(C)]
+#[derive(Debug, Copy, Clone)]
+pub struct btf_var_secinfo {
+    pub type_: __u32,
+    pub offset: __u32,
+    pub size: __u32,
+}

src/generated/btf_internal_bindings.rs

@@ -0,0 +1,86 @@
+/* automatically generated by rust-bindgen 0.55.1 */
+
+#[repr(C)]
+#[derive(Default)]
+pub struct __IncompleteArrayField<T>(::std::marker::PhantomData<T>, [T; 0]);
+impl<T> __IncompleteArrayField<T> {
+    #[inline]
+    pub const fn new() -> Self {
+        __IncompleteArrayField(::std::marker::PhantomData, [])
+    }
+    #[inline]
+    pub fn as_ptr(&self) -> *const T {
+        self as *const _ as *const T
+    }
+    #[inline]
+    pub fn as_mut_ptr(&mut self) -> *mut T {
+        self as *mut _ as *mut T
+    }
+    #[inline]
+    pub unsafe fn as_slice(&self, len: usize) -> &[T] {
+        ::std::slice::from_raw_parts(self.as_ptr(), len)
+    }
+    #[inline]
+    pub unsafe fn as_mut_slice(&mut self, len: usize) -> &mut [T] {
+        ::std::slice::from_raw_parts_mut(self.as_mut_ptr(), len)
+    }
+}
+impl<T> ::std::fmt::Debug for __IncompleteArrayField<T> {
+    fn fmt(&self, fmt: &mut ::std::fmt::Formatter<'_>) -> ::std::fmt::Result {
+        fmt.write_str("__IncompleteArrayField")
+    }
+}
+pub type __u8 = ::std::os::raw::c_uchar;
+pub type __u16 = ::std::os::raw::c_ushort;
+pub type __u32 = ::std::os::raw::c_uint;
+#[repr(C)]
+#[derive(Debug, Copy, Clone)]
+pub struct btf_ext_info {
+    pub info: *mut ::std::os::raw::c_void,
+    pub rec_size: __u32,
+    pub len: __u32,
+}
+#[repr(C)]
+#[derive(Debug, Copy, Clone)]
+pub struct btf_ext_header {
+    pub magic: __u16,
+    pub version: __u8,
+    pub flags: __u8,
+    pub hdr_len: __u32,
+    pub func_info_off: __u32,
+    pub func_info_len: __u32,
+    pub line_info_off: __u32,
+    pub line_info_len: __u32,
+    pub core_relo_off: __u32,
+    pub core_relo_len: __u32,
+}
+#[repr(C)]
+#[derive(Debug)]
+pub struct btf_ext_info_sec {
+    pub sec_name_off: __u32,
+    pub num_info: __u32,
+    pub data: __IncompleteArrayField<__u8>,
+}
+pub mod bpf_core_relo_kind {
+    pub type Type = ::std::os::raw::c_uint;
+    pub const BPF_FIELD_BYTE_OFFSET: Type = 0;
+    pub const BPF_FIELD_BYTE_SIZE: Type = 1;
+    pub const BPF_FIELD_EXISTS: Type = 2;
+    pub const BPF_FIELD_SIGNED: Type = 3;
+    pub const BPF_FIELD_LSHIFT_U64: Type = 4;
+    pub const BPF_FIELD_RSHIFT_U64: Type = 5;
+    pub const BPF_TYPE_ID_LOCAL: Type = 6;
+    pub const BPF_TYPE_ID_TARGET: Type = 7;
+    pub const BPF_TYPE_EXISTS: Type = 8;
+    pub const BPF_TYPE_SIZE: Type = 9;
+    pub const BPF_ENUMVAL_EXISTS: Type = 10;
+    pub const BPF_ENUMVAL_VALUE: Type = 11;
+}
+#[repr(C)]
+#[derive(Debug, Copy, Clone)]
+pub struct bpf_core_relo {
+    pub insn_off: __u32,
+    pub type_id: __u32,
+    pub access_str_off: __u32,
+    pub kind: bpf_core_relo_kind::Type,
+}

src/generated/mod.rs

@@ -3,7 +3,11 @@
 // FIXME: generate for x86_64 and aarch64
 
 mod bpf_bindings;
+mod btf_bindings;
+mod btf_internal_bindings;
 mod perf_bindings;
 
 pub use bpf_bindings::*;
+pub use btf_bindings::*;
+pub use btf_internal_bindings::*;
 pub use perf_bindings::*;

src/obj/btf/btf.rs

@@ -0,0 +1,381 @@
+use std::{
+    borrow::Cow,
+    convert::TryInto,
+    ffi::{c_void, CStr},
+    mem, ptr,
+};
+
+use thiserror::Error;
+
+use crate::generated::{btf_ext_header, btf_header};
+
+use super::{BtfType, Relocation};
+
+unsafe impl object::pod::Pod for btf_header {}
+unsafe impl object::pod::Pod for btf_ext_header {}
+
+pub(crate) const MAX_RESOLVE_DEPTH: u8 = 32;
+pub(crate) const MAX_SPEC_LEN: usize = 64;
+
+#[derive(Error, Debug, Clone, Eq, PartialEq)]
+pub enum BtfError {
+    #[error("error parsing BTF header")]
+    InvalidHeader,
+
+    #[error("invalid type info segment")]
+    InvalidTypeInfo,
+
+    #[error("invalid relocation info segment")]
+    InvalidRelocationInfo,
+
+    #[error("invalid BTF type kind `{kind}`")]
+    InvalidTypeKind { kind: u32 },
+
+    #[error("invalid BTF relocation kind `{kind}`")]
+    InvalidRelocationKind { kind: u32 },
+
+    #[error("invalid BTF string offset: {offset}")]
+    InvalidStringOffset { offset: usize },
+
+    #[error("invalid BTF info, offset: {offset} len: {len} section_len: {section_len}")]
+    InvalidInfo {
+        offset: usize,
+        len: usize,
+        section_len: usize,
+    },
+
+    #[error("invalid BTF line info, offset: {offset} len: {len} section_len: {section_len}")]
+    InvalidLineInfo {
+        offset: usize,
+        len: usize,
+        section_len: usize,
+    },
+
+    #[error("Unknown BTF type id `{type_id}`")]
+    UnknownBtfType { type_id: u32 },
+
+    #[error("Unexpected BTF type id `{type_id}`")]
+    UnexpectedBtfType { type_id: u32 },
+
+    #[error("maximum depth reached resolving BTF type")]
+    MaximumTypeDepthReached { type_id: u32 },
+}
+
+#[derive(Clone, Debug)]
+pub struct Btf {
+    header: btf_header,
+    strings: Vec<u8>,
+    types: Vec<BtfType>,
+}
+
+impl Btf {
+    pub(crate) fn parse(data: &[u8]) -> Result<Btf, BtfError> {
+        if data.len() < mem::size_of::<btf_header>() {
+            return Err(BtfError::InvalidHeader);
+        }
+
+        // safety: btf_header is POD so read_unaligned is safe
+        let header = unsafe { ptr::read_unaligned(data.as_ptr() as *const btf_header) };
+
+        let str_off = header.hdr_len as usize + header.str_off as usize;
+        let str_len = header.str_len as usize;
+        if str_off + str_len > data.len() {
+            return Err(BtfError::InvalidHeader);
+        }
+
+        let strings = data[str_off..str_off + str_len].to_vec();
+        let types = Btf::read_type_info(&header, data)?;
+
+        Ok(Btf {
+            header,
+            strings,
+            types,
+        })
+    }
+
+    fn read_type_info(header: &btf_header, data: &[u8]) -> Result<Vec<BtfType>, BtfError> {
+        let hdr_len = header.hdr_len as usize;
+        let type_off = header.type_off as usize;
+        let type_len = header.type_len as usize;
+        let base = hdr_len + type_off;
+        if base + type_len > data.len() {
+            return Err(BtfError::InvalidTypeInfo);
+        }
+
+        let mut data = &data[base..base + type_len];
+        let mut types = vec![BtfType::Unknown];
+        while !data.is_empty() {
+            // Safety:
+            // read() reads POD values from ELF, which is sound, but the values can still contain
+            // internally inconsistent values (like out of bound offsets and such).
+            let ty = unsafe { BtfType::read(data)? };
+            data = &data[ty.type_info_size()..];
+            types.push(ty);
+        }
+
+        Ok(types)
+    }
+
+    pub(crate) fn string_at(&self, offset: u32) -> Result<Cow<'_, str>, BtfError> {
+        let btf_header {
+            hdr_len,
+            mut str_off,
+            str_len,
+            ..
+        } = self.header;
+        str_off += hdr_len;
+        if offset >= str_off + str_len {
+            return Err(BtfError::InvalidStringOffset {
+                offset: offset as usize,
+            });
+        }
+
+        let offset = offset as usize;
+        let nul = self.strings[offset..]
+            .iter()
+            .position(|c| *c == 0u8)
+            .ok_or(BtfError::InvalidStringOffset { offset })?;
+
+        let s = CStr::from_bytes_with_nul(&self.strings[offset..=offset + nul])
+            .map_err(|_| BtfError::InvalidStringOffset { offset })?;
+
+        Ok(s.to_string_lossy())
+    }
+
+    pub(crate) fn type_by_id(&self, type_id: u32) -> Result<&BtfType, BtfError> {
+        self.types
+            .get(type_id as usize)
+            .ok_or(BtfError::UnknownBtfType { type_id })
+    }
+
+    pub(crate) fn types(&self) -> impl Iterator<Item = &BtfType> {
+        self.types.iter()
+    }
+
+    pub(crate) fn resolve_type(&self, root_type_id: u32) -> Result<u32, BtfError> {
+        let mut type_id = root_type_id;
+        for _ in 0..MAX_RESOLVE_DEPTH {
+            let ty = self.type_by_id(type_id)?;
+
+            use BtfType::*;
+            match ty {
+                Volatile(ty) | Const(ty) | Restrict(ty) | Typedef(ty) => {
+                    // Safety: union
+                    type_id = unsafe { ty.__bindgen_anon_1.type_ };
+                    continue;
+                }
+                _ => return Ok(type_id),
+            }
+        }
+
+        Err(BtfError::MaximumTypeDepthReached {
+            type_id: root_type_id,
+        })
+    }
+
+    pub(crate) fn type_name(&self, ty: &BtfType) -> Result<Option<Cow<'_, str>>, BtfError> {
+        ty.name_offset()
+            .map(|off| Ok(self.string_at(off)?))
+            .transpose()
+    }
+
+    pub(crate) fn err_type_name(&self, ty: &BtfType) -> Option<String> {
+        ty.name_offset()
+            .and_then(|off| self.string_at(off).ok().map(String::from))
+    }
+
+    pub(crate) fn type_size(&self, root_type_id: u32) -> Result<usize, BtfError> {
+        let mut type_id = root_type_id;
+        let mut n_elems = 1;
+        for _ in 0..MAX_RESOLVE_DEPTH {
+            let ty = self.type_by_id(type_id)?;
+
+            use BtfType::*;
+            let size = match ty {
+                Int(ty, _) | Struct(ty, _) | Union(ty, _) | Enum(ty, _) | DataSec(ty, _) => {
+                    // Safety: union
+                    unsafe { ty.__bindgen_anon_1.size as usize }
+                }
+                Ptr(_) => mem::size_of::<*const c_void>(), // FIXME
+                Typedef(ty) | Volatile(ty) | Const(ty) | Restrict(ty) | Var(ty, _) => {
+                    // Safety: union
+                    type_id = unsafe { ty.__bindgen_anon_1.type_ };
+                    continue;
+                }
+                Array(_, array) => {
+                    n_elems *= array.nelems as usize;
+                    type_id = array.type_;
+                    continue;
+                }
+                Unknown | Fwd(_) | Func(_) | FuncProto(_, _) => {
+                    return Err(BtfError::UnexpectedBtfType { type_id })
+                }
+            };
+
+            return Ok(size * n_elems);
+        }
+
+        Err(BtfError::MaximumTypeDepthReached {
+            type_id: root_type_id,
+        })
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct BtfExt {
+    data: Vec<u8>,
+    relocations: Vec<(u32, Vec<Relocation>)>,
+    header: btf_ext_header,
+    func_info_rec_size: usize,
+    line_info_rec_size: usize,
+    core_relo_rec_size: usize,
+}
+
+impl BtfExt {
+    pub(crate) fn parse(data: &[u8]) -> Result<BtfExt, BtfError> {
+        // Safety: btf_ext_header is POD so read_unaligned is safe
+        let header = unsafe {
+            ptr::read_unaligned::<btf_ext_header>(data.as_ptr() as *const btf_ext_header)
+        };
+
+        let rec_size = |offset, len| {
+            let offset = mem::size_of::<btf_ext_header>() + offset as usize;
+            let len = len as usize;
+            // check that there's at least enough space for the `rec_size` field
+            if (len > 0 && len < 4) || offset + len > data.len() {
+                return Err(BtfError::InvalidInfo {
+                    offset,
+                    len,
+                    section_len: data.len(),
+                });
+            }
+            Ok(if len > 0 {
+                /* FIXME: endianness */
+                u32::from_ne_bytes(data[offset..offset + 4].try_into().unwrap()) as usize
+            } else {
+                0
+            })
+        };
+
+        let btf_ext_header {
+            func_info_off,
+            func_info_len,
+            line_info_off,
+            line_info_len,
+            core_relo_off,
+            core_relo_len,
+            ..
+        } = header;
+
+        let mut ext = BtfExt {
+            header,
+            relocations: Vec::new(),
+            func_info_rec_size: rec_size(func_info_off, func_info_len)?,
+            line_info_rec_size: rec_size(line_info_off, line_info_len)?,
+            core_relo_rec_size: rec_size(core_relo_off, core_relo_len)?,
+            data: data.to_vec(),
+        };
+
+        let rec_size = ext.core_relo_rec_size;
+        ext.relocations.extend(
+            SecInfoIter::new(ext.core_relo_data(), ext.core_relo_rec_size)
+                .map(move |sec| {
+                    let relos = sec
+                        .data
+                        .chunks(rec_size)
+                        .enumerate()
+                        .map(|(n, rec)| unsafe { Relocation::parse(rec, n) })
+                        .collect::<Result<Vec<_>, _>>()?;
+                    Ok((sec.sec_name_off, relos))
+                })
+                .collect::<Result<Vec<_>, _>>()?,
+        );
+
+        Ok(ext)
+    }
+
+    fn info_data(&self, offset: u32, len: u32) -> &[u8] {
+        let offset = (self.header.hdr_len + offset) as usize;
+        let data = &self.data[offset..offset + len as usize];
+        if len > 0 {
+            // skip `rec_size`
+            &data[4..]
+        } else {
+            data
+        }
+    }
+
+    fn func_info_data(&self) -> &[u8] {
+        self.info_data(self.header.func_info_off, self.header.func_info_len)
+    }
+
+    fn line_info_data(&self) -> &[u8] {
+        self.info_data(self.header.line_info_off, self.header.line_info_len)
+    }
+
+    fn core_relo_data(&self) -> &[u8] {
+        self.info_data(self.header.core_relo_off, self.header.core_relo_len)
+    }
+
+    pub(crate) fn func_info(&self) -> SecInfoIter<'_> {
+        SecInfoIter::new(self.func_info_data(), self.func_info_rec_size)
+    }
+
+    pub(crate) fn line_info(&self) -> SecInfoIter<'_> {
+        SecInfoIter::new(self.line_info_data(), self.line_info_rec_size)
+    }
+
+    pub(crate) fn relocations(&self) -> impl Iterator<Item = &(u32, Vec<Relocation>)> {
+        self.relocations.iter()
+    }
+}
+
+pub(crate) struct SecInfoIter<'a> {
+    data: &'a [u8],
+    offset: usize,
+    rec_size: usize,
+}
+
+impl<'a> SecInfoIter<'a> {
+    fn new(data: &'a [u8], rec_size: usize) -> Self {
+        Self {
+            data,
+            rec_size,
+            offset: 0,
+        }
+    }
+}
+
+impl<'a> Iterator for SecInfoIter<'a> {
+    type Item = SecInfo<'a>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let data = self.data;
+        if self.offset + 8 >= data.len() {
+            return None;
+        }
+
+        // FIXME: endianness
+        let sec_name_off =
+            u32::from_ne_bytes(data[self.offset..self.offset + 4].try_into().unwrap());
+        self.offset += 4;
+        let num_info = u32::from_ne_bytes(data[self.offset..self.offset + 4].try_into().unwrap());
+        self.offset += 4;
+
+        let data = &data[self.offset..self.offset + (self.rec_size * num_info as usize)];
+        self.offset += self.rec_size * num_info as usize;
+
+        Some(SecInfo {
+            sec_name_off,
+            num_info,
+            data,
+        })
+    }
+}
+
+#[derive(Debug)]
+pub(crate) struct SecInfo<'a> {
+    sec_name_off: u32,
+    num_info: u32,
+    data: &'a [u8],
+}

src/obj/btf/mod.rs

@@ -0,0 +1,7 @@
+mod btf;
+mod relocation;
+mod types;
+
+pub use btf::*;
+pub(crate) use relocation::*;
+pub(crate) use types::*;

src/obj/btf/relocation.rs

@@ -0,0 +1,991 @@
+use std::{
+    collections::HashMap,
+    convert::{TryFrom, TryInto},
+    fs, io, mem, ptr,
+};
+
+use thiserror::Error;
+
+use crate::{
+    generated::{
+        bpf_core_relo, bpf_core_relo_kind::*, bpf_insn, BPF_ALU, BPF_ALU64, BPF_B, BPF_DW, BPF_H,
+        BPF_K, BPF_LD, BPF_LDX, BPF_ST, BPF_STX, BPF_W, BTF_INT_SIGNED,
+    },
+    obj::{
+        btf::{
+            fields_are_compatible, member_bit_field_size, member_bit_offset, types_are_compatible,
+            BtfType, MAX_SPEC_LEN,
+        },
+        Btf, BtfError, Object, Program,
+    },
+};
+
+#[derive(Error, Debug)]
+pub enum BtfRelocationError {
+    #[error("{error}")]
+    BtfError {
+        #[from]
+        error: BtfError,
+    },
+
+    #[error("{error}")]
+    IOError {
+        #[from]
+        error: io::Error,
+    },
+
+    #[error("section `{name}` not found")]
+    SectionNotFound { name: String },
+
+    #[error("invalid BTF relocation access string {access_str}")]
+    InvalidAccessString { access_str: String },
+
+    #[error("invalid instruction index #{index} referenced by relocation #{relocation_number} in section `{section_name}`")]
+    InvalidInstructionIndex {
+        index: usize,
+        num_instructions: usize,
+        section_name: String,
+        relocation_number: usize,
+    },
+
+    #[error("error relocating {type_name}, multiple candidate target types found with different memory layouts: {candidates:?}")]
+    ConflictingCandidates {
+        type_name: String,
+        candidates: Vec<String>,
+    },
+
+    #[error("maximum nesting level reached evaluating candidate type `{}`", err_type_name(.type_name))]
+    MaximumNestingLevelReached { type_name: Option<String> },
+
+    #[error("invalid access string `{spec}` for type `{}`: {error}", err_type_name(.type_name))]
+    InvalidAccessIndex {
+        type_name: Option<String>,
+        spec: String,
+        index: usize,
+        max_index: usize,
+        error: String,
+    },
+
+    #[error(
+        "relocation #{relocation_number} of kind `{relocation_kind}` not valid for type `{type_kind}`: {error}"
+    )]
+    InvalidRelocationKindForType {
+        relocation_number: usize,
+        relocation_kind: String,
+        type_kind: String,
+        error: String,
+    },
+
+    #[error(
+        "instruction #{index} referenced by relocation #{relocation_number} is invalid: {error}"
+    )]
+    InvalidInstruction {
+        relocation_number: usize,
+        index: usize,
+        error: String,
+    },
+}
+
+fn err_type_name(name: &Option<String>) -> String {
+    name.clone().unwrap_or_else(|| "[unknown name]".to_string())
+}
+
+#[derive(Copy, Clone, Debug)]
+#[repr(u32)]
+enum RelocationKind {
+    FieldByteOffset = BPF_FIELD_BYTE_OFFSET,
+    FieldByteSize = BPF_FIELD_BYTE_SIZE,
+    FieldExists = BPF_FIELD_EXISTS,
+    FieldSigned = BPF_FIELD_SIGNED,
+    FieldLShift64 = BPF_FIELD_LSHIFT_U64,
+    FieldRShift64 = BPF_FIELD_RSHIFT_U64,
+    TypeIdLocal = BPF_TYPE_ID_LOCAL,
+    TypeIdTarget = BPF_TYPE_ID_TARGET,
+    TypeExists = BPF_TYPE_EXISTS,
+    TypeSize = BPF_TYPE_SIZE,
+    EnumVariantExists = BPF_ENUMVAL_EXISTS,
+    EnumVariantValue = BPF_ENUMVAL_VALUE,
+}
+
+impl TryFrom<u32> for RelocationKind {
+    type Error = BtfError;
+
+    fn try_from(v: u32) -> Result<Self, Self::Error> {
+        use RelocationKind::*;
+
+        Ok(match v {
+            BPF_FIELD_BYTE_OFFSET => FieldByteOffset,
+            BPF_FIELD_BYTE_SIZE => FieldByteSize,
+            BPF_FIELD_EXISTS => FieldExists,
+            BPF_FIELD_SIGNED => FieldSigned,
+            BPF_FIELD_LSHIFT_U64 => FieldLShift64,
+            BPF_FIELD_RSHIFT_U64 => FieldRShift64,
+            BPF_TYPE_ID_LOCAL => TypeIdLocal,
+            BPF_TYPE_ID_TARGET => TypeIdTarget,
+            BPF_TYPE_EXISTS => TypeExists,
+            BPF_TYPE_SIZE => TypeSize,
+            BPF_ENUMVAL_EXISTS => EnumVariantExists,
+            BPF_ENUMVAL_VALUE => EnumVariantValue,
+            kind => return Err(BtfError::InvalidRelocationKind { kind }),
+        })
+    }
+}
+
+#[derive(Debug, Copy, Clone)]
+pub struct Relocation {
+    kind: RelocationKind,
+    ins_offset: usize,
+    type_id: u32,
+    access_str_offset: u32,
+    number: usize,
+}
+
+impl Relocation {
+    #[allow(unused_unsafe)]
+    pub(crate) unsafe fn parse(data: &[u8], number: usize) -> Result<Relocation, BtfError> {
+        if mem::size_of::<bpf_core_relo>() > data.len() {
+            return Err(BtfError::InvalidRelocationInfo);
+        }
+
+        let rel = unsafe { ptr::read_unaligned::<bpf_core_relo>(data.as_ptr() as *const _) };
+
+        Ok(Relocation {
+            kind: rel.kind.try_into()?,
+            ins_offset: rel.insn_off as usize,
+            type_id: rel.type_id,
+            access_str_offset: rel.access_str_off,
+            number,
+        })
+    }
+}
+
+impl Object {
+    pub fn relocate_btf(&mut self) -> Result<(), BtfRelocationError> {
+        let (local_btf, btf_ext) = match (&self.btf, &self.btf_ext) {
+            (Some(btf), Some(btf_ext)) => (btf, btf_ext),
+            _ => return Ok(()),
+        };
+
+        let target_btf = fs::read("/sys/kernel/btf/vmlinux")?;
+        let target_btf = Btf::parse(&target_btf)?;
+
+        let mut candidates_cache = HashMap::<u32, Vec<Candidate>>::new();
+
+        for (sec_name_off, relos) in btf_ext.relocations() {
+            let section_name = local_btf.string_at(*sec_name_off)?;
+
+            // FIXME
+            let parts = section_name.split("/").collect::<Vec<_>>();
+            if parts.len() < 2 {
+                continue;
+            }
+            let section_name = parts[1];
+            let program = self.programs.get_mut(section_name).ok_or_else(|| {
+                BtfRelocationError::SectionNotFound {
+                    name: section_name.to_string(),
+                }
+            })?;
+
+            for rel in relos {
+                let instructions = &mut program.instructions;
+                let ins_index = rel.ins_offset as usize / std::mem::size_of::<bpf_insn>();
+                if ins_index >= instructions.len() {
+                    return Err(BtfRelocationError::InvalidInstructionIndex {
+                        index: ins_index,
+                        num_instructions: instructions.len(),
+                        section_name: section_name.to_string(),
+                        relocation_number: rel.number,
+                    });
+                }
+
+                let local_ty = local_btf.type_by_id(rel.type_id)?;
+                let local_name = &*local_btf.type_name(local_ty)?.unwrap();
+                let access_str = &*local_btf.string_at(rel.access_str_offset)?;
+                let local_spec = AccessSpec::new(local_btf, rel.type_id, access_str, *rel)?;
+
+                let mut matches = match rel.kind {
+                    RelocationKind::TypeIdLocal => Vec::new(), // we don't need to look at target types to relocate this value
+                    _ => {
+                        let candidates = match candidates_cache.get(&rel.type_id) {
+                            Some(cands) => cands,
+                            None => {
+                                candidates_cache.insert(
+                                    rel.type_id,
+                                    find_candidates(local_ty, local_name, &target_btf)?,
+                                );
+                                candidates_cache.get(&rel.type_id).unwrap()
+                            }
+                        };
+
+                        let mut matches = Vec::new();
+                        for candidate in candidates {
+                            if let Some(candidate_spec) = match_candidate(&local_spec, candidate)? {
+                                let comp_rel = ComputedRelocation::new(
+                                    rel,
+                                    &local_spec,
+                                    Some(&candidate_spec),
+                                )?;
+                                matches.push((candidate.name.clone(), candidate_spec, comp_rel));
+                            }
+                        }
+
+                        matches
+                    }
+                };
+
+                let comp_rel = if !matches.is_empty() {
+                    let mut matches = matches.drain(..);
+                    let (_, target_spec, target_comp_rel) = matches.next().unwrap();
+
+                    // if there's more than one candidate, make sure that they all resolve to the
+                    // same value, else the relocation is ambiguous and can't be applied
+                    let conflicts = matches
+                        .filter_map(|(cand_name, cand_spec, cand_comp_rel)| {
+                            if cand_spec.bit_offset != target_spec.bit_offset
+                                || cand_comp_rel.target.value != target_comp_rel.target.value
+                            {
+                                Some(cand_name.clone())
+                            } else {
+                                None
+                            }
+                        })
+                        .collect::<Vec<_>>();
+                    if !conflicts.is_empty() {
+                        return Err(BtfRelocationError::ConflictingCandidates {
+                            type_name: local_name.to_string(),
+                            candidates: conflicts,
+                        });
+                    }
+                    target_comp_rel
+                } else {
+                    // there are no candidate matches and therefore no target_spec. This might mean
+                    // that matching failed, or that the relocation can be applied looking at local
+                    // types only
+                    ComputedRelocation::new(rel, &local_spec, None)?
+                };
+
+                comp_rel.apply(program, rel, section_name, local_btf, &target_btf)?;
+            }
+        }
+
+        Ok(())
+    }
+}
+
+fn find_candidates<'target>(
+    local_ty: &BtfType,
+    local_name: &str,
+    target_btf: &'target Btf,
+) -> Result<Vec<Candidate<'target>>, BtfError> {
+    let flavorless_name = |name: &str| name.splitn(2, "___").next().unwrap().to_string();
+
+    let mut candidates = Vec::new();
+    let local_name = flavorless_name(local_name);
+    for (type_id, ty) in target_btf.types().enumerate() {
+        if local_ty.kind()? != ty.kind()? {
+            continue;
+        }
+        let name = &*target_btf.type_name(ty)?.unwrap();
+        if local_name != flavorless_name(name) {
+            continue;
+        }
+
+        candidates.push(Candidate {
+            name: name.to_owned(),
+            btf: &target_btf,
+            ty,
+            type_id: type_id as u32,
+        });
+    }
+
+    Ok(candidates)
+}
+
+fn match_candidate<'target>(
+    local_spec: &AccessSpec,
+    candidate: &'target Candidate,
+) -> Result<Option<AccessSpec<'target>>, BtfRelocationError> {
+    let mut target_spec = AccessSpec {
+        btf: candidate.btf,
+        root_type_id: candidate.type_id,
+        relocation: local_spec.relocation,
+        parts: Vec::new(),
+        accessors: Vec::new(),
+        bit_offset: 0,
+    };
+
+    match local_spec.relocation.kind {
+        RelocationKind::TypeIdLocal
+        | RelocationKind::TypeIdTarget
+        | RelocationKind::TypeExists
+        | RelocationKind::TypeSize => {
+            if types_are_compatible(
+                local_spec.btf,
+                local_spec.root_type_id,
+                candidate.btf,
+                candidate.type_id,
+            )? {
+                return Ok(Some(target_spec));
+            } else {
+                return Ok(None);
+            }
+        }
+        RelocationKind::EnumVariantExists | RelocationKind::EnumVariantValue => todo!(),
+        RelocationKind::FieldByteOffset
+        | RelocationKind::FieldByteSize
+        | RelocationKind::FieldExists
+        | RelocationKind::FieldSigned
+        | RelocationKind::FieldLShift64
+        | RelocationKind::FieldRShift64 => {
+            let mut target_id = candidate.type_id;
+            for accessor in &local_spec.accessors {
+                target_id = candidate.btf.resolve_type(target_id)?;
+
+                if accessor.name.is_some() {
+                    if let Some(next_id) = match_member(
+                        local_spec.btf,
+                        &local_spec,
+                        accessor,
+                        candidate.btf,
+                        target_id,
+                        &mut target_spec,
+                    )? {
+                        target_id = next_id;
+                    } else {
+                        return Ok(None);
+                    }
+                } else {
+                    // array access
+
+                    if target_spec.parts.len() == MAX_SPEC_LEN {
+                        return Err(BtfRelocationError::MaximumNestingLevelReached {
+                            type_name: Some(candidate.name.clone()),
+                        });
+                    }
+
+                    target_spec.parts.push(accessor.index);
+                    target_spec.accessors.push(Accessor {
+                        index: accessor.index,
+                        type_id: target_id,
+                        name: None,
+                    });
+                    target_spec.bit_offset +=
+                        accessor.index * candidate.btf.type_size(target_id)? * 8;
+                }
+            }
+        }
+    };
+
+    Ok(Some(target_spec))
+}
+
+fn match_member<'local, 'target>(
+    local_btf: &Btf,
+    local_spec: &AccessSpec<'local>,
+    local_accessor: &Accessor,
+    target_btf: &'target Btf,
+    target_id: u32,
+    target_spec: &mut AccessSpec<'target>,
+) -> Result<Option<u32>, BtfRelocationError> {
+    let local_ty = local_btf.type_by_id(local_accessor.type_id)?;
+    let local_member = match local_ty {
+        BtfType::Struct(_, members) | BtfType::Union(_, members) => {
+            // this won't panic, bounds are checked when local_spec is built in AccessSpec::new
+            members[local_accessor.index]
+        }
+        _ => panic!("bug! this should only be called for structs and unions"),
+    };
+
+    let local_name = &*local_btf.string_at(local_member.name_off)?;
+    let target_id = target_btf.resolve_type(target_id)?;
+    let target_ty = target_btf.type_by_id(target_id)?;
+
+    let target_members = match target_ty {
+        BtfType::Struct(ty, members) | BtfType::Union(ty, members) => members,
+        // not a fields type, no match
+        _ => return Ok(None),
+    };
+
+    for (index, target_member) in target_members.iter().enumerate() {
+        if target_spec.parts.len() == MAX_SPEC_LEN {
+            let root_ty = target_spec.btf.type_by_id(target_spec.root_type_id)?;
+            return Err(BtfRelocationError::MaximumNestingLevelReached {
+                type_name: target_spec.btf.err_type_name(root_ty),
+            });
+        }
+
+        let bit_offset = member_bit_offset(target_ty.info().unwrap(), target_member);
+        let target_name = &*target_btf.string_at(target_member.name_off)?;
+
+        if target_name == "" {
+            let ret = match_member(
+                local_btf,
+                local_spec,
+                local_accessor,
+                target_btf,
+                target_member.type_,
+                target_spec,
+            )?;
+            if ret.is_some() {
+                target_spec.bit_offset += bit_offset;
+                target_spec.parts.push(index);
+                return Ok(ret);
+            }
+        } else if local_name == target_name {
+            if fields_are_compatible(
+                local_spec.btf,
+                local_member.type_,
+                target_btf,
+                target_member.type_,
+            )? {
+                target_spec.bit_offset += bit_offset;
+                target_spec.parts.push(index);
+                target_spec.accessors.push(Accessor {
+                    type_id: target_id,
+                    index,
+                    name: Some(target_name.to_owned()),
+                });
+                return Ok(Some(target_member.type_));
+            } else {
+                return Ok(None);
+            }
+        }
+    }
+
+    Ok(None)
+}
+
+#[derive(Debug)]
+struct AccessSpec<'a> {
+    btf: &'a Btf,
+    root_type_id: u32,
+    parts: Vec<usize>,
+    accessors: Vec<Accessor>,
+    relocation: Relocation,
+    bit_offset: usize,
+}
+
+impl<'a> AccessSpec<'a> {
+    fn new(
+        btf: &'a Btf,
+        root_type_id: u32,
+        spec: &str,
+        relocation: Relocation,
+    ) -> Result<AccessSpec<'a>, BtfRelocationError> {
+        let parts = spec
+            .split(":")
+            .map(|s| s.parse::<usize>())
+            .collect::<Result<Vec<_>, _>>()
+            .map_err(|_| BtfRelocationError::InvalidAccessString {
+                access_str: spec.to_string(),
+            })?;
+
+        let mut type_id = btf.resolve_type(root_type_id)?;
+        let ty = btf.type_by_id(type_id)?;
+
+        let spec = match relocation.kind {
+            RelocationKind::TypeIdLocal
+            | RelocationKind::TypeIdTarget
+            | RelocationKind::TypeExists
+            | RelocationKind::TypeSize => {
+                if parts != [0] {
+                    return Err(BtfRelocationError::InvalidAccessString {
+                        access_str: spec.to_string(),
+                    });
+                }
+                AccessSpec {
+                    btf,
+                    root_type_id,
+                    relocation,
+                    parts,
+                    accessors: Vec::new(),
+                    bit_offset: 0,
+                }
+            }
+            RelocationKind::EnumVariantExists | RelocationKind::EnumVariantValue => match ty {
+                BtfType::Enum(_, members) => {
+                    if parts.len() != 1 {
+                        return Err(BtfRelocationError::InvalidAccessString {
+                            access_str: spec.to_string(),
+                        });
+                    }
+                    let index = parts[0];
+                    if index >= members.len() {
+                        return Err(BtfRelocationError::InvalidAccessIndex {
+                            type_name: btf.err_type_name(ty),
+                            spec: spec.to_string(),
+                            index: index,
+                            max_index: members.len(),
+                            error: "tried to access nonexistant enum variant".to_string(),
+                        });
+                    }
+                    let accessors = vec![Accessor {
+                        type_id,
+                        index,
+                        name: btf.type_name(ty)?.map(String::from),
+                    }];
+
+                    AccessSpec {
+                        btf,
+                        root_type_id,
+                        relocation,
+                        parts,
+                        accessors,
+                        bit_offset: 0,
+                    }
+                }
+                _ => {
+                    return Err(BtfRelocationError::InvalidRelocationKindForType {
+                        relocation_number: relocation.number,
+                        relocation_kind: format!("{:?}", relocation.kind),
+                        type_kind: format!("{:?}", ty.kind()?.unwrap()),
+                        error: "enum relocation on non-enum type".to_string(),
+                    })
+                }
+            },
+
+            RelocationKind::FieldByteOffset
+            | RelocationKind::FieldByteSize
+            | RelocationKind::FieldExists
+            | RelocationKind::FieldSigned
+            | RelocationKind::FieldLShift64
+            | RelocationKind::FieldRShift64 => {
+                let mut accessors = vec![Accessor {
+                    type_id,
+                    index: parts[0],
+                    name: None,
+                }];
+                let mut bit_offset = accessors[0].index as usize * btf.type_size(type_id)?;
+                for index in parts.iter().skip(1).cloned() {
+                    type_id = btf.resolve_type(type_id)?;
+                    let ty = btf.type_by_id(type_id)?;
+
+                    use BtfType::*;
+                    match ty {
+                        Struct(t, members) | Union(t, members) => {
+                            if index >= members.len() {
+                                return Err(BtfRelocationError::InvalidAccessIndex {
+                                    type_name: btf.err_type_name(ty),
+                                    spec: spec.to_string(),
+                                    index: index,
+                                    max_index: members.len(),
+                                    error: "out of bounds struct or union access".to_string(),
+                                });
+                            }
+
+                            let member = members[index];
+                            bit_offset += member_bit_offset(t.info, &member);
+
+                            if member.name_off != 0 {
+                                accessors.push(Accessor {
+                                    type_id,
+                                    index,
+                                    name: Some(btf.string_at(member.name_off)?.to_string()),
+                                });
+                            }
+
+                            type_id = member.type_;
+                        }
+
+                        Array(_, array) => {
+                            type_id = btf.resolve_type(array.type_)?;
+                            let var_len = array.nelems == 0 && {
+                                // an array is potentially variable length if it's the last field
+                                // of the parent struct and has 0 elements
+                                let parent = accessors.last().unwrap();
+                                let parent_ty = btf.type_by_id(parent.type_id)?;
+                                match parent_ty {
+                                    Struct(_, members) => index == members.len() - 1,
+                                    _ => false,
+                                }
+                            };
+                            if !var_len && index >= array.nelems as usize {
+                                return Err(BtfRelocationError::InvalidAccessIndex {
+                                    type_name: btf.err_type_name(ty),
+                                    spec: spec.to_string(),
+                                    index,
+                                    max_index: array.nelems as usize,
+                                    error: "array index out of bounds".to_string(),
+                                });
+                            }
+                            accessors.push(Accessor {
+                                type_id,
+                                index,
+                                name: None,
+                            });
+                            let size = btf.type_size(type_id)?;
+                            bit_offset += index * size * 8;
+                        }
+                        rel_kind => {
+                            return Err(BtfRelocationError::InvalidRelocationKindForType {
+                                relocation_number: relocation.number,
+                                relocation_kind: format!("{:?}", rel_kind),
+                                type_kind: format!("{:?}", ty.kind()),
+                                error: "field relocation on a type that doesn't have fields"
+                                    .to_string(),
+                            });
+                        }
+                    };
+                }
+
+                AccessSpec {
+                    btf,
+                    root_type_id,
+                    relocation,
+                    parts,
+                    accessors,
+                    bit_offset,
+                }
+            }
+        };
+
+        Ok(spec)
+    }
+}
+
+#[derive(Debug)]
+struct Accessor {
+    type_id: u32,
+    index: usize,
+    name: Option<String>,
+}
+
+#[derive(Debug)]
+struct Candidate<'a> {
+    name: String,
+    btf: &'a Btf,
+    ty: &'a BtfType,
+    type_id: u32,
+}
+
+#[derive(Debug)]
+struct ComputedRelocation {
+    local: ComputedRelocationValue,
+    target: ComputedRelocationValue,
+}
+
+#[derive(Debug)]
+struct ComputedRelocationValue {
+    value: u32,
+    size: u32,
+    type_id: Option<u32>,
+}
+
+impl ComputedRelocation {
+    fn new(
+        rel: &Relocation,
+        local_spec: &AccessSpec,
+        target_spec: Option<&AccessSpec>,
+    ) -> Result<ComputedRelocation, BtfRelocationError> {
+        use RelocationKind::*;
+        let ret = match rel.kind {
+            FieldByteOffset | FieldByteSize | FieldExists | FieldSigned | FieldLShift64
+            | FieldRShift64 => ComputedRelocation {
+                local: Self::compute_field_relocation(rel, Some(local_spec))?,
+                target: Self::compute_field_relocation(rel, target_spec)?,
+            },
+            TypeIdLocal | TypeIdTarget | TypeExists | TypeSize => ComputedRelocation {
+                local: Self::compute_type_relocation(rel, local_spec, target_spec)?,
+                target: Self::compute_type_relocation(rel, local_spec, target_spec)?,
+            },
+            EnumVariantExists | EnumVariantValue => ComputedRelocation {
+                local: Self::compute_enum_relocation(rel, Some(local_spec))?,
+                target: Self::compute_enum_relocation(rel, target_spec)?,
+            },
+        };
+
+        Ok(ret)
+    }
+
+    fn apply(
+        &self,
+        program: &mut Program,
+        rel: &Relocation,
+        section_name: &str,
+        local_btf: &Btf,
+        target_btf: &Btf,
+    ) -> Result<(), BtfRelocationError> {
+        let instructions = &mut program.instructions;
+        let num_instructions = instructions.len();
+        let ins_index = rel.ins_offset as usize / std::mem::size_of::<bpf_insn>();
+        let mut ins =
+            instructions
+                .get_mut(ins_index)
+                .ok_or(BtfRelocationError::InvalidInstructionIndex {
+                    index: rel.ins_offset as usize,
+                    num_instructions,
+                    section_name: section_name.to_string(),
+                    relocation_number: rel.number,
+                })?;
+
+        let class = (ins.code & 0x07) as u32;
+
+        let target_value = self.target.value;
+
+        match class {
+            BPF_ALU | BPF_ALU64 => {
+                let src_reg = ins.src_reg();
+                if src_reg != BPF_K as u8 {
+                    return Err(BtfRelocationError::InvalidInstruction {
+                        relocation_number: rel.number,
+                        index: ins_index,
+                        error: format!("invalid src_reg={:x} expected {:x}", src_reg, BPF_K),
+                    });
+                }
+
+                ins.imm = target_value as i32;
+            }
+            BPF_LDX | BPF_ST | BPF_STX => {
+                if target_value > std::i16::MAX as u32 {
+                    return Err(BtfRelocationError::InvalidInstruction {
+                        relocation_number: rel.number,
+                        index: ins_index,
+                        error: format!("value `{}` overflows 16 bits offset field", target_value),
+                    });
+                }
+
+                ins.off = target_value as i16;
+
+                if self.local.size != self.target.size {
+                    let local_ty = local_btf.type_by_id(self.local.type_id.unwrap())?;
+                    let target_ty = target_btf.type_by_id(self.target.type_id.unwrap())?;
+                    let unsigned = |info: u32| ((info >> 24) & 0x0F) & BTF_INT_SIGNED == 0;
+                    use BtfType::*;
+                    match (local_ty, target_ty) {
+                        (Ptr(_), Ptr(_)) => {}
+                        (Int(_, local_info), Int(_, target_info))
+                            if unsigned(*local_info) && unsigned(*target_info) => {}
+                        _ => {
+                            return Err(BtfRelocationError::InvalidInstruction {
+                                relocation_number: rel.number,
+                                index: ins_index,
+                                error: format!(
+                                    "original type {} has size {} but target type {} has size {}",
+                                    err_type_name(&local_btf.err_type_name(local_ty)),
+                                    self.local.size,
+                                    err_type_name(&target_btf.err_type_name(target_ty)),
+                                    self.target.size,
+                                ),
+                            })
+                        }
+                    }
+
+                    let size = match self.target.size {
+                        8 => BPF_DW,
+                        4 => BPF_W,
+                        2 => BPF_H,
+                        1 => BPF_B,
+                        size => {
+                            return Err(BtfRelocationError::InvalidInstruction {
+                                relocation_number: rel.number,
+                                index: ins_index,
+                                error: format!("invalid target size {}", size),
+                            })
+                        }
+                    } as u8;
+                    ins.code = ins.code & 0xE0 | size | ins.code & 0x07;
+                }
+            }
+            BPF_LD => {
+                ins.imm = target_value as i32;
+                let mut next_ins = instructions.get_mut(ins_index + 1).ok_or(
+                    BtfRelocationError::InvalidInstructionIndex {
+                        index: ins_index + 1,
+                        num_instructions,
+                        section_name: section_name.to_string(),
+                        relocation_number: rel.number,
+                    },
+                )?;
+
+                next_ins.imm = 0;
+            }
+            class => {
+                return Err(BtfRelocationError::InvalidInstruction {
+                    relocation_number: rel.number,
+                    index: ins_index,
+                    error: format!("invalid instruction class {:x}", class),
+                })
+            }
+        };
+
+        Ok(())
+    }
+
+    fn compute_enum_relocation(
+        rel: &Relocation,
+        spec: Option<&AccessSpec>,
+    ) -> Result<ComputedRelocationValue, BtfRelocationError> {
+        use RelocationKind::*;
+        let value = match rel.kind {
+            EnumVariantExists => spec.is_some() as u32,
+            EnumVariantValue => {
+                let spec = spec.unwrap();
+                let accessor = &spec.accessors[0];
+                match spec.btf.type_by_id(accessor.type_id)? {
+                    BtfType::Enum(_, variants) => variants[accessor.index].val as u32,
+                    _ => panic!("should not be reached"),
+                }
+            }
+            // this function is only called for enum relocations
+            _ => panic!("should not be reached"),
+        };
+
+        Ok(ComputedRelocationValue {
+            value,
+            size: 0,
+            type_id: None,
+        })
+    }
+
+    fn compute_field_relocation(
+        rel: &Relocation,
+        spec: Option<&AccessSpec>,
+    ) -> Result<ComputedRelocationValue, BtfRelocationError> {
+        use RelocationKind::*;
+
+        if let FieldExists = rel.kind {
+            // this is the bpf_preserve_field_info(member_access, FIELD_EXISTENCE) case. If we
+            // managed to build a spec, it means the field exists.
+            return Ok(ComputedRelocationValue {
+                value: spec.is_some() as u32,
+                size: 0,
+                type_id: None,
+            });
+        }
+
+        let spec = spec.unwrap();
+        let accessor = spec.accessors.last().unwrap();
+        if accessor.name.is_none() {
+            // the last accessor is unnamed, meaning that this is an array access
+            return match rel.kind {
+                FieldByteOffset => Ok(ComputedRelocationValue {
+                    value: (spec.bit_offset / 8) as u32,
+                    size: spec.btf.type_size(accessor.type_id)? as u32,
+                    type_id: Some(accessor.type_id),
+                }),
+                FieldByteSize => Ok(ComputedRelocationValue {
+                    value: spec.btf.type_size(accessor.type_id)? as u32,
+                    size: 0,
+                    type_id: Some(accessor.type_id),
+                }),
+                rel_kind => {
+                    let ty = spec.btf.type_by_id(accessor.type_id)?;
+                    return Err(BtfRelocationError::InvalidRelocationKindForType {
+                        relocation_number: rel.number,
+                        relocation_kind: format!("{:?}", rel_kind),
+                        type_kind: format!("{:?}", ty.kind()),
+                        error: "invalid relocation kind for array type".to_string(),
+                    });
+                }
+            };
+        }
+
+        let ty = spec.btf.type_by_id(accessor.type_id)?;
+        let (ll_ty, member) = match ty {
+            BtfType::Struct(ty, members) | BtfType::Union(ty, members) => {
+                (ty, members[accessor.index])
+            }
+            _ => {
+                return Err(BtfRelocationError::InvalidRelocationKindForType {
+                    relocation_number: rel.number,
+                    relocation_kind: format!("{:?}", rel.kind),
+                    type_kind: format!("{:?}", ty.kind()),
+                    error: "field relocation on a type that doesn't have fields".to_string(),
+                });
+            }
+        };
+
+        let bit_off = spec.bit_offset as u32;
+        let member_type_id = spec.btf.resolve_type(member.type_)?;
+        let member_ty = spec.btf.type_by_id(member_type_id)?;
+        let ll_member_ty = member_ty.btf_type().unwrap();
+
+        let mut byte_size;
+        let mut byte_off;
+        let mut bit_size = member_bit_field_size(ll_ty, &member) as u32;
+        let is_bitfield = bit_size > 0;
+        if is_bitfield {
+            // find out the smallest int size to load the bitfield
+            byte_size = unsafe { ll_member_ty.__bindgen_anon_1.size };
+            byte_off = bit_off / 8 / byte_size * byte_size;
+            while bit_off + bit_size - byte_off * 8 > byte_size * 8 {
+                if byte_size >= 8 {
+                    // the bitfield is larger than 8 bytes!?
+                    return Err(BtfError::InvalidTypeInfo)?;
+                }
+                byte_size *= 2;
+                byte_off = bit_off / 8 / byte_size * byte_size;
+            }
+        } else {
+            byte_size = spec.btf.type_size(member_type_id)? as u32;
+            bit_size = byte_size * 8;
+            byte_off = spec.bit_offset as u32 / 8;
+        }
+
+        let mut value = ComputedRelocationValue {
+            value: 0,
+            size: 0,
+            type_id: None,
+        };
+        match rel.kind {
+            FieldByteOffset => {
+                value.value = byte_off;
+                if !is_bitfield {
+                    value.size = byte_size;
+                    value.type_id = Some(member_type_id);
+                }
+            }
+            FieldByteSize => {
+                value.value = byte_size;
+            }
+            FieldSigned => match member_ty {
+                BtfType::Enum(_, _) => value.value = 1,
+                BtfType::Int(_, i) => value.value = ((i >> 24) & 0x0F) & BTF_INT_SIGNED,
+                _ => (),
+            },
+            #[cfg(target_endian = "little")]
+            FieldLShift64 => {
+                value.value = 64 - (bit_off + bit_size - byte_off * 8);
+            }
+            #[cfg(target_endian = "big")]
+            FieldLShift64 => {
+                value.value = (8 - byte_size) * 8 + (bit_off - byte_off * 8);
+            }
+            FieldRShift64 => {
+                value.value = 64 - bit_size;
+            }
+            FieldExists // this is handled at the start of the function
+            | _ => panic!("bug! this should not be reached"),
+        }
+
+        Ok(value)
+    }
+
+    fn compute_type_relocation(
+        rel: &Relocation,
+        local_spec: &AccessSpec,
+        target_spec: Option<&AccessSpec>,
+    ) -> Result<ComputedRelocationValue, BtfRelocationError> {
+        use RelocationKind::*;
+        let value = match rel.kind {
+            TypeIdLocal => local_spec.root_type_id,
+            _ => match target_spec {
+                Some(target_spec) => match rel.kind {
+                    TypeIdTarget => target_spec.root_type_id,
+                    TypeExists => 1,
+                    TypeSize => target_spec.btf.type_size(target_spec.root_type_id)? as u32,
+                    _ => panic!("bug! this should not be reached"),
+                },
+                // FIXME in the case of TypeIdTarget and TypeSize this should probably fail the
+                // relocation...
+                None => 0,
+            },
+        };
+
+        Ok(ComputedRelocationValue {
+            value,
+            size: 0,
+            type_id: None,
+        })
+    }
+}

src/obj/btf/types.rs

@@ -0,0 +1,388 @@
+use std::{
+    convert::{TryFrom, TryInto},
+    mem, ptr,
+};
+
+use crate::{
+    generated::{
+        btf_array, btf_enum, btf_member, btf_param, btf_type, btf_type__bindgen_ty_1, btf_var,
+        btf_var_secinfo, BTF_KIND_ARRAY, BTF_KIND_CONST, BTF_KIND_DATASEC, BTF_KIND_ENUM,
+        BTF_KIND_FUNC, BTF_KIND_FUNC_PROTO, BTF_KIND_FWD, BTF_KIND_INT, BTF_KIND_PTR,
+        BTF_KIND_RESTRICT, BTF_KIND_STRUCT, BTF_KIND_TYPEDEF, BTF_KIND_UNION, BTF_KIND_UNKN,
+        BTF_KIND_VAR, BTF_KIND_VOLATILE,
+    },
+    obj::btf::{Btf, BtfError, MAX_RESOLVE_DEPTH},
+};
+
+unsafe impl object::pod::Pod for btf_type {}
+
+#[derive(Clone, Debug)]
+pub(crate) enum BtfType {
+    Unknown,
+    Fwd(btf_type),
+    Const(btf_type),
+    Volatile(btf_type),
+    Restrict(btf_type),
+    Ptr(btf_type),
+    Typedef(btf_type),
+    Func(btf_type),
+    Int(btf_type, u32),
+    Enum(btf_type, Vec<btf_enum>),
+    Array(btf_type, btf_array),
+    Struct(btf_type, Vec<btf_member>),
+    Union(btf_type, Vec<btf_member>),
+    FuncProto(btf_type, Vec<btf_param>),
+    Var(btf_type, btf_var),
+    DataSec(btf_type, Vec<btf_var_secinfo>),
+}
+
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+#[repr(u32)]
+pub(crate) enum BtfKind {
+    Unknown = BTF_KIND_UNKN,
+    Int = BTF_KIND_INT,
+    Ptr = BTF_KIND_PTR,
+    Array = BTF_KIND_ARRAY,
+    Struct = BTF_KIND_STRUCT,
+    Union = BTF_KIND_UNION,
+    Enum = BTF_KIND_ENUM,
+    Fwd = BTF_KIND_FWD,
+    Typedef = BTF_KIND_TYPEDEF,
+    Volatile = BTF_KIND_VOLATILE,
+    Const = BTF_KIND_CONST,
+    Restrict = BTF_KIND_RESTRICT,
+    Func = BTF_KIND_FUNC,
+    FuncProto = BTF_KIND_FUNC_PROTO,
+    Var = BTF_KIND_VAR,
+    DataSec = BTF_KIND_DATASEC,
+}
+
+impl TryFrom<u32> for BtfKind {
+    type Error = BtfError;
+
+    fn try_from(v: u32) -> Result<Self, Self::Error> {
+        use BtfKind::*;
+        Ok(match v {
+            BTF_KIND_UNKN => Unknown,
+            BTF_KIND_INT => Int,
+            BTF_KIND_PTR => Ptr,
+            BTF_KIND_ARRAY => Array,
+            BTF_KIND_STRUCT => Struct,
+            BTF_KIND_UNION => Union,
+            BTF_KIND_ENUM => Enum,
+            BTF_KIND_FWD => Fwd,
+            BTF_KIND_TYPEDEF => Typedef,
+            BTF_KIND_VOLATILE => Volatile,
+            BTF_KIND_CONST => Const,
+            BTF_KIND_RESTRICT => Restrict,
+            BTF_KIND_FUNC => Func,
+            BTF_KIND_FUNC_PROTO => FuncProto,
+            BTF_KIND_VAR => Var,
+            BTF_KIND_DATASEC => DataSec,
+            kind => return Err(BtfError::InvalidTypeKind { kind }),
+        })
+    }
+}
+
+unsafe fn read<T>(data: &[u8]) -> Result<T, BtfError> {
+    if mem::size_of::<T>() > data.len() {
+        return Err(BtfError::InvalidTypeInfo);
+    }
+
+    Ok(ptr::read_unaligned::<T>(data.as_ptr() as *const T))
+}
+
+unsafe fn read_array<T>(data: &[u8], len: usize) -> Result<Vec<T>, BtfError> {
+    if mem::size_of::<T>() * len > data.len() {
+        return Err(BtfError::InvalidTypeInfo);
+    }
+
+    Ok((0..len)
+        .map(|i| {
+            ptr::read_unaligned::<T>((data.as_ptr() as usize + i * mem::size_of::<T>()) as *const T)
+        })
+        .collect::<Vec<T>>())
+}
+
+impl BtfType {
+    #[allow(unused_unsafe)]
+    pub(crate) unsafe fn read(data: &[u8]) -> Result<BtfType, BtfError> {
+        let ty = unsafe { read::<btf_type>(data)? };
+        let data = &data[mem::size_of::<btf_type>()..];
+
+        let vlen = type_vlen(&ty) as usize;
+        use BtfType::*;
+        Ok(match type_kind(&ty)? {
+            BtfKind::Unknown => Unknown,
+            BtfKind::Fwd => Fwd(ty),
+            BtfKind::Const => Const(ty),
+            BtfKind::Volatile => Volatile(ty),
+            BtfKind::Restrict => Restrict(ty),
+            BtfKind::Ptr => Ptr(ty),
+            BtfKind::Typedef => Typedef(ty),
+            BtfKind::Func => Func(ty),
+            BtfKind::Int => {
+                // FIXME: endianness
+                if mem::size_of::<u32>() > data.len() {
+                    return Err(BtfError::InvalidTypeInfo);
+                }
+                Int(
+                    ty,
+                    u32::from_ne_bytes(data[..mem::size_of::<u32>()].try_into().unwrap()),
+                )
+            }
+            BtfKind::Enum => Enum(ty, unsafe { read_array(data, vlen)? }),
+            BtfKind::Array => Array(ty, unsafe { read(data)? }),
+            BtfKind::Struct => Struct(ty, unsafe { read_array(data, vlen)? }),
+            BtfKind::Union => Union(ty, unsafe { read_array(data, vlen)? }),
+            BtfKind::FuncProto => FuncProto(ty, unsafe { read_array(data, vlen)? }),
+            BtfKind::Var => Var(ty, unsafe { read(data)? }),
+            BtfKind::DataSec => DataSec(ty, unsafe { read_array(data, vlen)? }),
+        })
+    }
+
+    pub(crate) fn type_info_size(&self) -> usize {
+        let ty_size = mem::size_of::<btf_type>();
+
+        use BtfType::*;
+        match self {
+            Unknown => 0,
+            Fwd(_) | Const(_) | Volatile(_) | Restrict(_) | Ptr(_) | Typedef(_) | Func(_) => {
+                ty_size
+            }
+            Int(_, _) => ty_size + mem::size_of::<u32>(),
+            Enum(ty, _) => ty_size + type_vlen(ty) * mem::size_of::<btf_enum>(),
+            Array(_, _) => ty_size + mem::size_of::<btf_array>(),
+            Struct(ty, _) => ty_size + type_vlen(ty) * mem::size_of::<btf_member>(),
+            Union(ty, _) => ty_size + type_vlen(ty) * mem::size_of::<btf_member>(),
+            FuncProto(ty, _) => ty_size + type_vlen(ty) * mem::size_of::<btf_param>(),
+            Var(_, _) => ty_size + mem::size_of::<btf_var>(),
+            DataSec(ty, _) => ty_size + type_vlen(ty) * mem::size_of::<btf_var_secinfo>(),
+        }
+    }
+
+    pub(crate) fn btf_type(&self) -> Option<&btf_type> {
+        use BtfType::*;
+        Some(match self {
+            Unknown => return None,
+            Fwd(ty) => ty,
+            Const(ty) => ty,
+            Volatile(ty) => ty,
+            Restrict(ty) => ty,
+            Ptr(ty) => ty,
+            Typedef(ty) => ty,
+            Func(ty) => ty,
+            Int(ty, _) => ty,
+            Enum(ty, _) => ty,
+            Array(ty, _) => ty,
+            Struct(ty, _) => ty,
+            Union(ty, _) => ty,
+            FuncProto(ty, _) => ty,
+            Var(ty, _) => ty,
+            DataSec(ty, _) => ty,
+        })
+    }
+
+    pub(crate) fn info(&self) -> Option<u32> {
+        self.btf_type().map(|ty| ty.info)
+    }
+
+    pub(crate) fn name_offset(&self) -> Option<u32> {
+        self.btf_type().map(|ty| ty.name_off)
+    }
+
+    pub(crate) fn kind(&self) -> Result<Option<BtfKind>, BtfError> {
+        self.btf_type().map(type_kind).transpose()
+    }
+
+    pub(crate) fn is_composite(&self) -> bool {
+        match self {
+            BtfType::Struct(_, _) | BtfType::Union(_, _) => true,
+            _ => false,
+        }
+    }
+}
+
+fn type_kind(ty: &btf_type) -> Result<BtfKind, BtfError> {
+    ((ty.info >> 24) & 0x0F).try_into()
+}
+
+fn type_vlen(ty: &btf_type) -> usize {
+    (ty.info & 0xFFFF) as usize
+}
+
+pub(crate) fn member_bit_offset(info: u32, member: &btf_member) -> usize {
+    let k_flag = info >> 31 == 1;
+    let bit_offset = if k_flag {
+        member.offset & 0xFFFFFF
+    } else {
+        member.offset
+    };
+
+    bit_offset as usize
+}
+
+pub(crate) fn member_bit_field_size(ty: &btf_type, member: &btf_member) -> usize {
+    let k_flag = (ty.info >> 31) == 1;
+    let size = if k_flag { member.offset >> 24 } else { 0 };
+
+    size as usize
+}
+
+pub(crate) fn types_are_compatible(
+    local_btf: &Btf,
+    root_local_id: u32,
+    target_btf: &Btf,
+    root_target_id: u32,
+) -> Result<bool, BtfError> {
+    let mut local_id = root_local_id;
+    let mut target_id = root_target_id;
+    let local_ty = local_btf.type_by_id(local_id)?;
+    let target_ty = target_btf.type_by_id(target_id)?;
+
+    if local_ty.kind()? != target_ty.kind()? {
+        return Ok(false);
+    }
+
+    for _ in 0..MAX_RESOLVE_DEPTH {
+        local_id = local_btf.resolve_type(local_id)?;
+        target_id = target_btf.resolve_type(target_id)?;
+        let local_ty = local_btf.type_by_id(local_id)?;
+        let target_ty = target_btf.type_by_id(target_id)?;
+
+        if local_ty.kind()? != target_ty.kind()? {
+            return Ok(false);
+        }
+
+        use BtfType::*;
+        match local_ty {
+            Unknown | Struct(_, _) | Union(_, _) | Enum(_, _) | Fwd(_) => return Ok(true),
+            Int(_, local_off) => {
+                if let Int(_, target_off) = target_ty {
+                    return Ok(*local_off == 0 && *target_off == 0);
+                }
+            }
+            Ptr(l_ty) => {
+                if let Ptr(t_ty) = target_ty {
+                    // Safety: union
+                    unsafe {
+                        local_id = l_ty.__bindgen_anon_1.type_;
+                        target_id = t_ty.__bindgen_anon_1.type_;
+                    }
+                    continue;
+                }
+            }
+            Array(l_ty, _) => {
+                if let Array(t_ty, _) = target_ty {
+                    // Safety: union
+                    unsafe {
+                        local_id = l_ty.__bindgen_anon_1.type_;
+                        target_id = t_ty.__bindgen_anon_1.type_;
+                    }
+                    continue;
+                }
+            }
+            FuncProto(l_ty, l_params) => {
+                if let FuncProto(t_ty, t_params) = target_ty {
+                    if l_params.len() != t_params.len() {
+                        return Ok(false);
+                    }
+
+                    for (l_param, t_param) in l_params.iter().zip(t_params.iter()) {
+                        let local_id = local_btf.resolve_type(l_param.type_)?;
+                        let target_id = target_btf.resolve_type(t_param.type_)?;
+                        if !types_are_compatible(local_btf, local_id, target_btf, target_id)? {
+                            return Ok(false);
+                        }
+                    }
+
+                    // Safety: union
+                    unsafe {
+                        local_id = l_ty.__bindgen_anon_1.type_;
+                        target_id = t_ty.__bindgen_anon_1.type_;
+                    }
+                    continue;
+                }
+            }
+            _ => panic!("this shouldn't be reached"),
+        }
+    }
+
+    Err(BtfError::MaximumTypeDepthReached { type_id: local_id })
+}
+
+pub(crate) fn fields_are_compatible(
+    local_btf: &Btf,
+    mut local_id: u32,
+    target_btf: &Btf,
+    mut target_id: u32,
+) -> Result<bool, BtfError> {
+    for _ in 0..MAX_RESOLVE_DEPTH {
+        local_id = local_btf.resolve_type(local_id)?;
+        target_id = target_btf.resolve_type(target_id)?;
+        let local_ty = local_btf.type_by_id(local_id)?;
+        let target_ty = target_btf.type_by_id(target_id)?;
+
+        if local_ty.is_composite() && target_ty.is_composite() {
+            return Ok(true);
+        }
+
+        if local_ty.kind()? != target_ty.kind()? {
+            return Ok(false);
+        }
+
+        use BtfType::*;
+        match local_ty {
+            Fwd(_) | Enum(_, _) => {
+                let flavorless_name =
+                    |name: &str| name.splitn(2, "___").next().unwrap().to_string();
+
+                let local_name = flavorless_name(&*local_btf.type_name(local_ty)?.unwrap());
+                let target_name = flavorless_name(&*target_btf.type_name(target_ty)?.unwrap());
+
+                return Ok(local_name == target_name);
+            }
+            Int(_, local_off) => {
+                let local_off = (local_off >> 16) & 0xFF;
+                if let Int(_, target_off) = target_ty {
+                    let target_off = (target_off >> 16) & 0xFF;
+                    return Ok(local_off == 0 && target_off == 0);
+                }
+            }
+            Ptr(_) => return Ok(true),
+            Array(l_ty, _) => {
+                if let Array(t_ty, _) = target_ty {
+                    // Safety: union
+                    unsafe {
+                        local_id = l_ty.__bindgen_anon_1.type_;
+                        target_id = t_ty.__bindgen_anon_1.type_;
+                    }
+                    continue;
+                }
+            }
+            _ => panic!("this shouldn't be reached"),
+        }
+    }
+
+    Err(BtfError::MaximumTypeDepthReached { type_id: local_id })
+}
+
+impl std::fmt::Debug for btf_type {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("btf_type")
+            .field("name_off", &self.name_off)
+            .field("info", &self.info)
+            .field("__bindgen_anon_1", &self.__bindgen_anon_1)
+            .finish()
+    }
+}
+
+impl std::fmt::Debug for btf_type__bindgen_ty_1 {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        // Safety: union
+        f.debug_struct("btf_type__bindgen_ty_1")
+            .field("size", unsafe { &self.size })
+            .field("type_", unsafe { &self.type_ })
+            .finish()
+    }
+}

src/obj/mod.rs

@@ -1,3 +1,4 @@
+mod btf;
 mod relocation;
 
 use object::{
@@ -14,7 +15,8 @@ use std::{
 };
 use thiserror::Error;
 
-pub use self::relocation::{relocate, RelocationError};
+use btf::{Btf, BtfError, BtfExt};
+pub use relocation::*;
 
 use crate::{
     bpf_map_def,
@@ -24,11 +26,13 @@ use crate::{
 
 const KERNEL_VERSION_ANY: u32 = 0xFFFF_FFFE;
 
-#[derive(Debug, Clone)]
+#[derive(Clone)]
 pub struct Object {
     pub(crate) endianness: Endianness,
     pub license: CString,
     pub kernel_version: KernelVersion,
+    pub btf: Option<Btf>,
+    pub btf_ext: Option<BtfExt>,
     pub(crate) maps: HashMap<String, Map>,
     pub(crate) programs: HashMap<String, Program>,
     pub(crate) relocations: HashMap<SectionIndex, Vec<Relocation>>,
@@ -100,6 +104,8 @@ impl Object {
             endianness: endianness.into(),
             license,
             kernel_version,
+            btf: None,
+            btf_ext: None,
             maps: HashMap::new(),
             programs: HashMap::new(),
             relocations: HashMap::new(),
@@ -135,6 +141,9 @@ pub enum ParseError {
         source: object::read::Error,
     },
 
+    #[error("Error parsing BTF: {0}")]
+    BTF(#[from] BtfError),
+
     #[error("no license specified")]
     MissingLicense,
 
@@ -193,7 +202,7 @@ impl<'data, 'file, 's> TryFrom<&'s Section<'data, 'file>> for BPFSection<'s> {
             relocations: section
                 .relocations()
                 .map(|(offset, r)| {
-                    Ok(Relocation {
+                    Ok::<_, ParseError>(Relocation {
                         kind: r.kind(),
                         target: r.target(),
                         addend: r.addend(),
@@ -321,6 +330,17 @@ fn parse_program(bpf: &Object, section: &BPFSection, ty: &str) -> Result<Program
     })
 }
 
+fn parse_btf(obj: &mut Object, section: &BPFSection) -> Result<(), BtfError> {
+    obj.btf = Some(Btf::parse(section.data)?);
+
+    Ok(())
+}
+
+fn parse_btf_ext(obj: &mut Object, section: &BPFSection) -> Result<(), BtfError> {
+    obj.btf_ext = Some(BtfExt::parse(section.data)?);
+    Ok(())
+}
+
 fn parse_section(bpf: &mut Object, section: BPFSection) -> Result<(), ParseError> {
     let parts = section.name.split("/").collect::<Vec<_>>();
 
@@ -329,6 +349,8 @@ fn parse_section(bpf: &mut Object, section: BPFSection) -> Result<(), ParseError
             bpf.maps
                 .insert(name.to_string(), parse_map(&section, name)?);
         }
+        &[".BTF"] => parse_btf(bpf, &section)?,
+        &[".BTF.ext"] => parse_btf_ext(bpf, &section)?,
         &["maps", name] => {
             bpf.maps
                 .insert(name.to_string(), parse_map(&section, name)?);

src/obj/relocation.rs

@@ -1,15 +1,15 @@
-use std::collections::HashMap;
+use std::{collections::HashMap, io};
 
 use object::{RelocationKind, RelocationTarget, SectionIndex};
 use thiserror::Error;
 
-use super::Object;
 use crate::{
     generated::{bpf_insn, BPF_PSEUDO_MAP_FD, BPF_PSEUDO_MAP_VALUE},
     maps::Map,
+    obj::{btf::BtfRelocationError, Object},
 };
 
-#[derive(Debug, Clone, Error)]
+#[derive(Debug, Error)]
 pub enum RelocationError {
     #[error("unknown symbol, index `{index}`")]
     UnknownSymbol { index: usize },
@@ -19,7 +19,7 @@ pub enum RelocationError {
 
     #[error("section `{section_index}` not found, referenced by symbol `{}`",
             .symbol_name.clone().unwrap_or_else(|| .symbol_index.to_string()))]
-    RelocationSectionNotFound {
+    SectionNotFound {
         section_index: usize,
         symbol_index: usize,
         symbol_name: Option<String>,
@@ -28,8 +28,24 @@ pub enum RelocationError {
     #[error("the map `{name}` at section `{section_index}` has not been created")]
     MapNotCreated { section_index: usize, name: String },
 
-    #[error("invalid relocation offset `{offset}`")]
-    InvalidRelocationOffset { offset: u64 },
+    #[error("invalid instruction index `{index}` referenced by relocation #{relocation_number}")]
+    InvalidInstructionIndex {
+        index: usize,
+        num_instructions: usize,
+        relocation_number: usize,
+    },
+
+    #[error("BTF error: {error}")]
+    BtfRelocationError {
+        #[from]
+        error: BtfRelocationError,
+    },
+
+    #[error("IO error: {io_error}")]
+    IO {
+        #[from]
+        io_error: io::Error,
+    },
 }
 
 #[derive(Debug, Copy, Clone)]
@@ -47,62 +63,73 @@ pub(crate) struct Symbol {
     pub(crate) address: u64,
 }
 
-pub fn relocate(obj: &mut Object, maps: &[Map]) -> Result<(), RelocationError> {
-    let maps_by_section = maps
-        .iter()
-        .map(|map| (map.obj.section_index, map))
-        .collect::<HashMap<_, _>>();
-
-    for program in obj.programs.values_mut() {
-        if let Some(relocations) = obj.relocations.get(&program.section_index) {
-            for rel in relocations {
-                match rel.target {
-                    RelocationTarget::Symbol(index) => {
-                        let sym = obj
-                            .symbol_table
-                            .get(&index)
-                            .ok_or(RelocationError::UnknownSymbol { index: index.0 })?;
-
-                        let section_index = sym
-                            .section_index
-                            .ok_or(RelocationError::UnknownSymbolSection { index: index.0 })?;
-
-                        let map = maps_by_section.get(&section_index.0).ok_or(
-                            RelocationError::RelocationSectionNotFound {
-                                symbol_index: index.0,
-                                symbol_name: sym.name.clone(),
+impl Object {
+    pub fn relocate(&mut self, maps: &[Map]) -> Result<(), RelocationError> {
+        self.relocate_maps(maps)?;
+        self.relocate_btf()?;
+
+        Ok(())
+    }
+
+    pub fn relocate_maps(&mut self, maps: &[Map]) -> Result<(), RelocationError> {
+        let maps_by_section = maps
+            .iter()
+            .map(|map| (map.obj.section_index, map))
+            .collect::<HashMap<_, _>>();
+
+        for program in self.programs.values_mut() {
+            if let Some(relocations) = self.relocations.get(&program.section_index) {
+                for (rel_n, rel) in relocations.iter().enumerate() {
+                    match rel.target {
+                        RelocationTarget::Symbol(index) => {
+                            let sym = self
+                                .symbol_table
+                                .get(&index)
+                                .ok_or(RelocationError::UnknownSymbol { index: index.0 })?;
+
+                            let section_index = sym
+                                .section_index
+                                .ok_or(RelocationError::UnknownSymbolSection { index: index.0 })?;
+
+                            let map = maps_by_section.get(&section_index.0).ok_or(
+                                RelocationError::SectionNotFound {
+                                    symbol_index: index.0,
+                                    symbol_name: sym.name.clone(),
+                                    section_index: section_index.0,
+                                },
+                            )?;
+
+                            let map_fd = map.fd.ok_or_else(|| RelocationError::MapNotCreated {
+                                name: map.obj.name.clone(),
                                 section_index: section_index.0,
-                            },
-                        )?;
-
-                        let map_fd = map.fd.ok_or_else(|| RelocationError::MapNotCreated {
-                            name: map.obj.name.clone(),
-                            section_index: section_index.0,
-                        })?;
-
-                        let instructions = &mut program.instructions;
-                        let ins_index =
-                            (rel.offset / std::mem::size_of::<bpf_insn>() as u64) as usize;
-                        if ins_index >= instructions.len() {
-                            return Err(RelocationError::InvalidRelocationOffset {
-                                offset: rel.offset,
-                            });
-                        }
-                        if !map.obj.data.is_empty() {
-                            instructions[ins_index].set_src_reg(BPF_PSEUDO_MAP_VALUE as u8);
-                            instructions[ins_index + 1].imm =
-                                instructions[ins_index].imm + sym.address as i32;
-                        } else {
-                            instructions[ins_index].set_src_reg(BPF_PSEUDO_MAP_FD as u8);
+                            })?;
+
+                            let instructions = &mut program.instructions;
+                            let ins_index =
+                                (rel.offset / std::mem::size_of::<bpf_insn>() as u64) as usize;
+                            if ins_index >= instructions.len() {
+                                return Err(RelocationError::InvalidInstructionIndex {
+                                    index: ins_index,
+                                    num_instructions: instructions.len(),
+                                    relocation_number: rel_n,
+                                });
+                            }
+                            if !map.obj.data.is_empty() {
+                                instructions[ins_index].set_src_reg(BPF_PSEUDO_MAP_VALUE as u8);
+                                instructions[ins_index + 1].imm =
+                                    instructions[ins_index].imm + sym.address as i32;
+                            } else {
+                                instructions[ins_index].set_src_reg(BPF_PSEUDO_MAP_FD as u8);
+                            }
+                            instructions[ins_index].imm = map_fd;
                         }
-                        instructions[ins_index].imm = map_fd;
+                        RelocationTarget::Section(_index) => {}
+                        RelocationTarget::Absolute => todo!(),
                     }
-                    RelocationTarget::Section(_index) => {}
-                    RelocationTarget::Absolute => todo!(),
                 }
             }
         }
-    }
 
-    Ok(())
+        Ok(())
+    }
 }