Skip to content

Commit

Permalink
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
aya: Implement .kconfig support
Browse files Browse the repository at this point in the history
Implement support for external data symbols (kconfig) following libbpf
logic.
marysaka authored and davibe committed Sep 2, 2024
1 parent ab000ad commit da75812
Showing 15 changed files with 485 additions and 24 deletions.
212 changes: 209 additions & 3 deletions aya-obj/src/btf/btf.rs
Original file line number Diff line number Diff line change
@@ -18,11 +18,12 @@ use crate::{
info::{FuncSecInfo, LineSecInfo},
relocation::Relocation,
Array, BtfEnum, BtfKind, BtfMember, BtfType, Const, Enum, FuncInfo, FuncLinkage, Int,
IntEncoding, LineInfo, Struct, Typedef, Union, VarLinkage,
IntEncoding, LineInfo, Struct, Typedef, Union, Var, VarLinkage,
},
generated::{btf_ext_header, btf_header},
generated::{bpf_map_type, btf_ext_header, btf_header, BPF_F_RDONLY_PROG},
maps::{bpf_map_def, LegacyMap},
util::{bytes_of, HashMap},
Object,
EbpfSectionKind, Map, Object,
};

pub(crate) const MAX_RESOLVE_DEPTH: u8 = 32;
@@ -157,6 +158,20 @@ pub enum BtfError {
/// unable to get symbol name
#[error("Unable to get symbol name")]
InvalidSymbolName,

/// external symbol is invalid
#[error("Invalid extern symbol `{symbol_name}`")]
InvalidExternalSymbol {
/// name of the symbol
symbol_name: String,
},

/// external symbol not found
#[error("Extern symbol not found `{symbol_name}`")]
ExternalSymbolNotFound {
/// name of the symbol
symbol_name: String,
},
}

/// Available BTF features
@@ -463,6 +478,57 @@ impl Btf {
})
}

pub(crate) fn type_align(&self, root_type_id: u32) -> Result<usize, BtfError> {
let mut type_id = root_type_id;
for _ in 0..MAX_RESOLVE_DEPTH {
let ty = self.types.type_by_id(type_id)?;
let size = match ty {
BtfType::Array(Array { array, .. }) => {
type_id = array.element_type;
continue;
}
BtfType::Struct(Struct { size, members, .. })
| BtfType::Union(Union { size, members, .. }) => {
let mut max_align = 1;

for m in members {
let align = self.type_align(m.btf_type)?;
max_align = usize::max(align, max_align);

if ty.member_bit_field_size(m).unwrap() == 0
|| m.offset % (8 * align as u32) != 0
{
return Ok(1);
}
}

if size % max_align as u32 != 0 {
return Ok(1);
}

return Ok(max_align);
}

other => {
if let Some(size) = other.size() {
u32::min(BtfType::ptr_size(), size)
} else if let Some(next) = other.btf_type() {
type_id = next;
continue;
} else {
return Err(BtfError::UnexpectedBtfType { type_id });
}
}
};

return Ok(size as usize);
}

Err(BtfError::MaximumTypeDepthReached {
type_id: root_type_id,
})
}

/// Encodes the metadata as BTF format
pub fn to_bytes(&self) -> Vec<u8> {
// Safety: btf_header is POD
@@ -473,6 +539,37 @@ impl Btf {
buf
}

pub(crate) fn get_extern_data_sec_entry_info(
&self,
target_var_name: &str,
) -> Result<(String, Var), BtfError> {
for t in &self.types.types {
if let BtfType::DataSec(d) = t {
let sec_name = self.string_at(d.name_offset)?;

for d in &d.entries {
if let BtfType::Var(var) = self.types.type_by_id(d.btf_type)? {
let var_name = self.string_at(var.name_offset)?;

if target_var_name == var_name {
if var.linkage != VarLinkage::Extern {
return Err(BtfError::InvalidExternalSymbol {
symbol_name: var_name.into(),
});
}

return Ok((sec_name.into(), var.clone()));
}
}
}
}
}

Err(BtfError::ExternalSymbolNotFound {
symbol_name: target_var_name.into(),
})
}

// This follows the same logic as libbpf's bpf_object__sanitize_btf() function.
// https://github.com/libbpf/libbpf/blob/05f94ddbb837f5f4b3161e341eed21be307eaa04/src/libbpf.c#L2701
//
@@ -610,6 +707,14 @@ impl Btf {
}
};
e.offset = *offset as u32;

if var.linkage == VarLinkage::Extern {
let mut var = var.clone();
var.linkage = VarLinkage::Global;

types.types[e.btf_type as usize] = BtfType::Var(var);
}

debug!(
"{} {}: VAR {}: fixup offset {}",
kind, name, var_name, offset
@@ -730,6 +835,107 @@ impl Default for Btf {
}

impl Object {
fn patch_extern_data_internal(
&mut self,
externs: &HashMap<String, Vec<u8>>,
) -> Result<Option<(SectionIndex, Vec<u8>)>, BtfError> {
if let Some(ref mut obj_btf) = &mut self.btf {
if obj_btf.is_empty() {
return Ok(None);
}

let mut kconfig_map_index = 0;

for map in self.maps.values() {
if map.section_index() >= kconfig_map_index {
kconfig_map_index = map.section_index() + 1;
}
}

let kconfig_map_index = self.maps.len();

let symbols = self
.symbol_table
.iter_mut()
.filter(|(_, s)| s.name.is_some() && s.section_index.is_none() && s.is_external)
.map(|(_, s)| (s.name.as_ref().unwrap().clone(), s));

let mut section_data = Vec::<u8>::new();
let mut offset = 0u64;
let mut has_extern_data = false;

for (name, symbol) in symbols {
let (datasec_name, var) = obj_btf.get_extern_data_sec_entry_info(&name)?;

if datasec_name == ".kconfig" {
has_extern_data = true;

let type_size = obj_btf.type_size(var.btf_type)?;
let type_align = obj_btf.type_align(var.btf_type)? as u64;

let mut external_value_opt = externs.get(&name);
let empty_data = vec![0; type_size];

if external_value_opt.is_none() && symbol.is_weak {
external_value_opt = Some(&empty_data);
}

if let Some(data) = external_value_opt {
symbol.address = (offset + (type_align - 1)) & !(type_align - 1);
symbol.size = type_size as u64;
symbol.section_index = Some(kconfig_map_index);

section_data.resize((symbol.address - offset) as usize, 0);

self.symbol_offset_by_name.insert(name, symbol.address);
section_data.extend(data);
offset = symbol.address + data.len() as u64;
} else {
return Err(BtfError::ExternalSymbolNotFound { symbol_name: name });
}
}
}

if has_extern_data {
self.section_infos.insert(
".kconfig".into(),
(SectionIndex(kconfig_map_index), section_data.len() as u64),
);

return Ok(Some((SectionIndex(kconfig_map_index), section_data)));
}
}
Ok(None)
}

/// Patches extern data
pub fn patch_extern_data(
&mut self,
externs: &HashMap<String, Vec<u8>>,
) -> Result<(), BtfError> {
if let Some((section_index, data)) = self.patch_extern_data_internal(externs)? {
self.maps.insert(
".kconfig".into(),
Map::Legacy(LegacyMap {
def: bpf_map_def {
map_type: bpf_map_type::BPF_MAP_TYPE_ARRAY as u32,
key_size: mem::size_of::<u32>() as u32,
value_size: data.len() as u32,
max_entries: 1,
map_flags: BPF_F_RDONLY_PROG,
..Default::default()
},
section_index: section_index.0,
section_kind: EbpfSectionKind::Rodata,
symbol_index: None,
data,
}),
);
}

Ok(())
}

/// Fixes up and sanitizes BTF data.
///
/// Mostly, it removes unsupported types and works around LLVM behaviours.
6 changes: 5 additions & 1 deletion aya-obj/src/btf/types.rs
Original file line number Diff line number Diff line change
@@ -1292,11 +1292,15 @@ impl BtfType {
BtfType::Struct(t) => Some(t.size),
BtfType::Union(t) => Some(t.size),
BtfType::DataSec(t) => Some(t.size),
BtfType::Ptr(_) => Some(mem::size_of::<&()>() as u32),
BtfType::Ptr(_) => Some(Self::ptr_size()),
_ => None,
}
}

pub(crate) fn ptr_size() -> u32 {
mem::size_of::<&()>() as u32
}

pub(crate) fn btf_type(&self) -> Option<u32> {
match self {
BtfType::Const(t) => Some(t.btf_type),
13 changes: 13 additions & 0 deletions aya-obj/src/obj.rs
Original file line number Diff line number Diff line change
@@ -47,6 +47,7 @@ pub struct Features {
bpf_cookie: bool,
cpumap_prog_id: bool,
devmap_prog_id: bool,
bpf_syscall_wrapper: bool,
btf: Option<BtfFeatures>,
}

@@ -61,6 +62,7 @@ impl Features {
bpf_cookie: bool,
cpumap_prog_id: bool,
devmap_prog_id: bool,
bpf_syscall_wrapper: bool,
btf: Option<BtfFeatures>,
) -> Self {
Self {
@@ -71,6 +73,7 @@ impl Features {
bpf_cookie,
cpumap_prog_id,
devmap_prog_id,
bpf_syscall_wrapper,
btf,
}
}
@@ -109,6 +112,10 @@ impl Features {
pub fn devmap_prog_id(&self) -> bool {
self.devmap_prog_id
}
/// Returns whether BPF syscall wrapper hooking is supported.
pub fn bpf_syscall_wrapper(&self) -> bool {
self.bpf_syscall_wrapper
}

/// If BTF is supported, returns which BTF features are supported.
pub fn btf(&self) -> Option<&BtfFeatures> {
@@ -464,6 +471,8 @@ impl Object {
address: symbol.address(),
size: symbol.size(),
is_definition: symbol.is_definition(),
is_external: symbol.is_undefined() && (symbol.is_global() || symbol.is_weak()),
is_weak: symbol.is_weak(),
kind: symbol.kind(),
};
bpf_obj.symbol_table.insert(symbol.index().0, sym);
@@ -1440,6 +1449,8 @@ mod tests {
size,
is_definition: false,
kind: SymbolKind::Text,
is_external: false,
is_weak: false,
},
);
obj.symbols_by_section
@@ -2576,6 +2587,8 @@ mod tests {
address: 0,
size: 3,
is_definition: true,
is_external: false,
is_weak: false,
kind: SymbolKind::Data,
},
);
17 changes: 12 additions & 5 deletions aya-obj/src/relocation.rs
Original file line number Diff line number Diff line change
@@ -99,6 +99,8 @@ pub(crate) struct Symbol {
pub(crate) address: u64,
pub(crate) size: u64,
pub(crate) is_definition: bool,
pub(crate) is_external: bool,
pub(crate) is_weak: bool,
pub(crate) kind: SymbolKind,
}

@@ -218,7 +220,9 @@ fn relocate_maps<'a, I: Iterator<Item = &'a Relocation>>(
};

// calls and relocation to .text symbols are handled in a separate step
if insn_is_call(&instructions[ins_index]) || text_sections.contains(&section_index) {
if insn_is_call(&instructions[ins_index])
|| (text_sections.contains(&section_index) && !sym.is_external)
{
continue;
}

@@ -367,10 +371,11 @@ impl<'a> FunctionLinker<'a> {
// only consider text relocations, data relocations are
// relocated in relocate_maps()
sym.kind == SymbolKind::Text
|| sym
.section_index
.map(|section_index| self.text_sections.contains(&section_index))
.unwrap_or(false)
|| (!sym.is_external
&& sym
.section_index
.map(|section_index| self.text_sections.contains(&section_index))
.unwrap_or(false))
});

// not a call and not a text relocation, we don't need to do anything
@@ -510,6 +515,8 @@ mod test {
address,
size,
is_definition: false,
is_external: false,
is_weak: false,
kind: SymbolKind::Data,
}
}
8 changes: 7 additions & 1 deletion aya/Cargo.toml
Original file line number Diff line number Diff line change
@@ -23,7 +23,13 @@ libc = { workspace = true }
log = { workspace = true }
object = { workspace = true, features = ["elf", "read_core", "std", "write"] }
thiserror = { workspace = true }
tokio = { workspace = true, features = ["rt"], optional = true }
tokio = { workspace = true, features = [
"rt",
"macros",
"rt-multi-thread",
"net",
], optional = true }
flate2 = "1.0"

[dev-dependencies]
tempfile = { workspace = true }
Loading

0 comments on commit da75812

Please sign in to comment.