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gimli.rs
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gimli.rs
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//! Support for symbolication using the `gimli` crate on crates.io
//!
//! This is the default symbolication implementation for Rust.
use self::gimli::read::EndianSlice;
use self::gimli::NativeEndian as Endian;
use self::mmap::Mmap;
use self::stash::Stash;
use super::BytesOrWideString;
use super::ResolveWhat;
use super::SymbolName;
use addr2line::gimli;
use core::convert::TryInto;
use core::mem;
use core::u32;
use libc::c_void;
use mystd::ffi::OsString;
use mystd::fs::File;
use mystd::path::Path;
use mystd::prelude::v1::*;
#[cfg(backtrace_in_libstd)]
mod mystd {
pub use crate::*;
}
#[cfg(not(backtrace_in_libstd))]
extern crate std as mystd;
cfg_if::cfg_if! {
if #[cfg(windows)] {
#[path = "gimli/mmap_windows.rs"]
mod mmap;
} else if #[cfg(any(
target_os = "android",
target_os = "freebsd",
target_os = "fuchsia",
target_os = "haiku",
target_os = "ios",
target_os = "linux",
target_os = "macos",
target_os = "openbsd",
target_os = "solaris",
target_os = "illumos",
))] {
#[path = "gimli/mmap_unix.rs"]
mod mmap;
} else {
#[path = "gimli/mmap_fake.rs"]
mod mmap;
}
}
mod stash;
const MAPPINGS_CACHE_SIZE: usize = 4;
struct Mapping {
// 'static lifetime is a lie to hack around lack of support for self-referential structs.
cx: Context<'static>,
_map: Mmap,
stash: Stash,
}
enum Either<A, B> {
#[allow(dead_code)]
A(A),
B(B),
}
impl Mapping {
/// Creates a `Mapping` by ensuring that the `data` specified is used to
/// create a `Context` and it can only borrow from that or the `Stash` of
/// decompressed sections or auxiliary data.
fn mk<F>(data: Mmap, mk: F) -> Option<Mapping>
where
F: for<'a> FnOnce(&'a [u8], &'a Stash) -> Option<Context<'a>>,
{
Mapping::mk_or_other(data, move |data, stash| {
let cx = mk(data, stash)?;
Some(Either::B(cx))
})
}
/// Creates a `Mapping` from `data`, or if the closure decides to, returns a
/// different mapping.
fn mk_or_other<F>(data: Mmap, mk: F) -> Option<Mapping>
where
F: for<'a> FnOnce(&'a [u8], &'a Stash) -> Option<Either<Mapping, Context<'a>>>,
{
let stash = Stash::new();
let cx = match mk(&data, &stash)? {
Either::A(mapping) => return Some(mapping),
Either::B(cx) => cx,
};
Some(Mapping {
// Convert to 'static lifetimes since the symbols should
// only borrow `map` and `stash` and we're preserving them below.
cx: unsafe { core::mem::transmute::<Context<'_>, Context<'static>>(cx) },
_map: data,
stash: stash,
})
}
}
struct Context<'a> {
dwarf: addr2line::Context<EndianSlice<'a, Endian>>,
object: Object<'a>,
package: Option<gimli::DwarfPackage<EndianSlice<'a, Endian>>>,
}
impl<'data> Context<'data> {
fn new(
stash: &'data Stash,
object: Object<'data>,
sup: Option<Object<'data>>,
dwp: Option<Object<'data>>,
) -> Option<Context<'data>> {
let mut sections = gimli::Dwarf::load(|id| -> Result<_, ()> {
let data = object.section(stash, id.name()).unwrap_or(&[]);
Ok(EndianSlice::new(data, Endian))
})
.ok()?;
if let Some(sup) = sup {
sections
.load_sup(|id| -> Result<_, ()> {
let data = sup.section(stash, id.name()).unwrap_or(&[]);
Ok(EndianSlice::new(data, Endian))
})
.ok()?;
}
let dwarf = addr2line::Context::from_dwarf(sections).ok()?;
let mut package = None;
if let Some(dwp) = dwp {
package = Some(
gimli::DwarfPackage::load(
|id| -> Result<_, gimli::Error> {
let data = id
.dwo_name()
.and_then(|name| dwp.section(stash, name))
.unwrap_or(&[]);
Ok(EndianSlice::new(data, Endian))
},
EndianSlice::new(&[], Endian),
)
.ok()?,
);
}
Some(Context {
dwarf,
object,
package,
})
}
fn find_frames(
&'_ self,
stash: &'data Stash,
probe: u64,
) -> gimli::Result<addr2line::FrameIter<'_, EndianSlice<'data, Endian>>> {
use addr2line::{LookupContinuation, LookupResult};
let mut l = self.dwarf.find_frames(probe);
loop {
let (load, continuation) = match l {
LookupResult::Output(output) => break output,
LookupResult::Load { load, continuation } => (load, continuation),
};
l = continuation.resume(handle_split_dwarf(self.package.as_ref(), stash, load));
}
}
}
fn mmap(path: &Path) -> Option<Mmap> {
let file = File::open(path).ok()?;
let len = file.metadata().ok()?.len().try_into().ok()?;
unsafe { Mmap::map(&file, len) }
}
cfg_if::cfg_if! {
if #[cfg(windows)] {
mod coff;
use self::coff::{handle_split_dwarf, Object};
} else if #[cfg(any(
target_os = "macos",
target_os = "ios",
target_os = "tvos",
target_os = "watchos",
))] {
mod macho;
use self::macho::{handle_split_dwarf, Object};
} else {
mod elf;
use self::elf::{handle_split_dwarf, Object};
}
}
cfg_if::cfg_if! {
if #[cfg(windows)] {
mod libs_windows;
use libs_windows::native_libraries;
} else if #[cfg(any(
target_os = "macos",
target_os = "ios",
target_os = "tvos",
target_os = "watchos",
))] {
mod libs_macos;
use libs_macos::native_libraries;
} else if #[cfg(target_os = "illumos")] {
mod libs_illumos;
use libs_illumos::native_libraries;
} else if #[cfg(all(
any(
target_os = "linux",
target_os = "fuchsia",
target_os = "freebsd",
target_os = "openbsd",
target_os = "netbsd",
all(target_os = "android", feature = "dl_iterate_phdr"),
),
not(target_env = "uclibc"),
))] {
mod libs_dl_iterate_phdr;
use libs_dl_iterate_phdr::native_libraries;
#[path = "gimli/parse_running_mmaps_unix.rs"]
mod parse_running_mmaps;
} else if #[cfg(target_env = "libnx")] {
mod libs_libnx;
use libs_libnx::native_libraries;
} else if #[cfg(target_os = "haiku")] {
mod libs_haiku;
use libs_haiku::native_libraries;
} else {
// Everything else should doesn't know how to load native libraries.
fn native_libraries() -> Vec<Library> {
Vec::new()
}
}
}
#[derive(Default)]
struct Cache {
/// All known shared libraries that have been loaded.
libraries: Vec<Library>,
/// Mappings cache where we retain parsed dwarf information.
///
/// This list has a fixed capacity for its entire lifetime which never
/// increases. The `usize` element of each pair is an index into `libraries`
/// above where `usize::max_value()` represents the current executable. The
/// `Mapping` is corresponding parsed dwarf information.
///
/// Note that this is basically an LRU cache and we'll be shifting things
/// around in here as we symbolize addresses.
mappings: Vec<(usize, Mapping)>,
}
struct Library {
name: OsString,
/// Segments of this library loaded into memory, and where they're loaded.
segments: Vec<LibrarySegment>,
/// The "bias" of this library, typically where it's loaded into memory.
/// This value is added to each segment's stated address to get the actual
/// virtual memory address that the segment is loaded into. Additionally
/// this bias is subtracted from real virtual memory addresses to index into
/// debuginfo and the symbol table.
bias: usize,
}
struct LibrarySegment {
/// The stated address of this segment in the object file. This is not
/// actually where the segment is loaded, but rather this address plus the
/// containing library's `bias` is where to find it.
stated_virtual_memory_address: usize,
/// The size of this segment in memory.
len: usize,
}
// unsafe because this is required to be externally synchronized
pub unsafe fn clear_symbol_cache() {
Cache::with_global(|cache| cache.mappings.clear());
}
impl Cache {
fn new() -> Cache {
Cache {
mappings: Vec::with_capacity(MAPPINGS_CACHE_SIZE),
libraries: native_libraries(),
}
}
// unsafe because this is required to be externally synchronized
unsafe fn with_global(f: impl FnOnce(&mut Self)) {
// A very small, very simple LRU cache for debug info mappings.
//
// The hit rate should be very high, since the typical stack doesn't cross
// between many shared libraries.
//
// The `addr2line::Context` structures are pretty expensive to create. Its
// cost is expected to be amortized by subsequent `locate` queries, which
// leverage the structures built when constructing `addr2line::Context`s to
// get nice speedups. If we didn't have this cache, that amortization would
// never happen, and symbolicating backtraces would be ssssllllooooowwww.
static mut MAPPINGS_CACHE: Option<Cache> = None;
f(MAPPINGS_CACHE.get_or_insert_with(|| Cache::new()))
}
fn avma_to_svma(&self, addr: *const u8) -> Option<(usize, *const u8)> {
self.libraries
.iter()
.enumerate()
.filter_map(|(i, lib)| {
// First up, test if this `lib` has any segment containing the
// `addr` (handling relocation). If this check passes then we
// can continue below and actually translate the address.
//
// Note that we're using `wrapping_add` here to avoid overflow
// checks. It's been seen in the wild that the SVMA + bias
// computation overflows. It seems a bit odd that would happen
// but there's not a huge amount we can do about it other than
// probably just ignore those segments since they're likely
// pointing off into space. This originally came up in
// rust-lang/backtrace-rs#329.
if !lib.segments.iter().any(|s| {
let svma = s.stated_virtual_memory_address;
let start = svma.wrapping_add(lib.bias);
let end = start.wrapping_add(s.len);
let address = addr as usize;
start <= address && address < end
}) {
return None;
}
// Now that we know `lib` contains `addr`, we can offset with
// the bias to find the stated virtual memory address.
let svma = (addr as usize).wrapping_sub(lib.bias);
Some((i, svma as *const u8))
})
.next()
}
fn mapping_for_lib<'a>(&'a mut self, lib: usize) -> Option<(&'a mut Context<'a>, &'a Stash)> {
let idx = self.mappings.iter().position(|(idx, _)| *idx == lib);
// Invariant: after this conditional completes without early returning
// from an error, the cache entry for this path is at index 0.
if let Some(idx) = idx {
// When the mapping is already in the cache, move it to the front.
if idx != 0 {
let entry = self.mappings.remove(idx);
self.mappings.insert(0, entry);
}
} else {
// When the mapping is not in the cache, create a new mapping,
// insert it into the front of the cache, and evict the oldest cache
// entry if necessary.
let name = &self.libraries[lib].name;
let mapping = Mapping::new(name.as_ref())?;
if self.mappings.len() == MAPPINGS_CACHE_SIZE {
self.mappings.pop();
}
self.mappings.insert(0, (lib, mapping));
}
let mapping = &mut self.mappings[0].1;
let cx: &'a mut Context<'static> = &mut mapping.cx;
let stash: &'a Stash = &mapping.stash;
// don't leak the `'static` lifetime, make sure it's scoped to just
// ourselves
Some((
unsafe { mem::transmute::<&'a mut Context<'static>, &'a mut Context<'a>>(cx) },
stash,
))
}
}
pub unsafe fn resolve(what: ResolveWhat<'_>, cb: &mut dyn FnMut(&super::Symbol)) {
let addr = what.address_or_ip();
let mut call = |sym: Symbol<'_>| {
// Extend the lifetime of `sym` to `'static` since we are unfortunately
// required to here, but it's only ever going out as a reference so no
// reference to it should be persisted beyond this frame anyway.
let sym = mem::transmute::<Symbol<'_>, Symbol<'static>>(sym);
(cb)(&super::Symbol { inner: sym });
};
Cache::with_global(|cache| {
let (lib, addr) = match cache.avma_to_svma(addr as *const u8) {
Some(pair) => pair,
None => return,
};
// Finally, get a cached mapping or create a new mapping for this file, and
// evaluate the DWARF info to find the file/line/name for this address.
let (cx, stash) = match cache.mapping_for_lib(lib) {
Some((cx, stash)) => (cx, stash),
None => return,
};
let mut any_frames = false;
if let Ok(mut frames) = cx.find_frames(stash, addr as u64) {
while let Ok(Some(frame)) = frames.next() {
any_frames = true;
let name = match frame.function {
Some(f) => Some(f.name.slice()),
None => cx.object.search_symtab(addr as u64),
};
call(Symbol::Frame {
addr: addr as *mut c_void,
location: frame.location,
name,
});
}
}
if !any_frames {
if let Some((object_cx, object_addr)) = cx.object.search_object_map(addr as u64) {
if let Ok(mut frames) = object_cx.find_frames(stash, object_addr) {
while let Ok(Some(frame)) = frames.next() {
any_frames = true;
call(Symbol::Frame {
addr: addr as *mut c_void,
location: frame.location,
name: frame.function.map(|f| f.name.slice()),
});
}
}
}
}
if !any_frames {
if let Some(name) = cx.object.search_symtab(addr as u64) {
call(Symbol::Symtab {
addr: addr as *mut c_void,
name,
});
}
}
});
}
pub enum Symbol<'a> {
/// We were able to locate frame information for this symbol, and
/// `addr2line`'s frame internally has all the nitty gritty details.
Frame {
addr: *mut c_void,
location: Option<addr2line::Location<'a>>,
name: Option<&'a [u8]>,
},
/// Couldn't find debug information, but we found it in the symbol table of
/// the elf executable.
Symtab { addr: *mut c_void, name: &'a [u8] },
}
impl Symbol<'_> {
pub fn name(&self) -> Option<SymbolName<'_>> {
match self {
Symbol::Frame { name, .. } => {
let name = name.as_ref()?;
Some(SymbolName::new(name))
}
Symbol::Symtab { name, .. } => Some(SymbolName::new(name)),
}
}
pub fn addr(&self) -> Option<*mut c_void> {
match self {
Symbol::Frame { addr, .. } => Some(*addr),
Symbol::Symtab { .. } => None,
}
}
pub fn filename_raw(&self) -> Option<BytesOrWideString<'_>> {
match self {
Symbol::Frame { location, .. } => {
let file = location.as_ref()?.file?;
Some(BytesOrWideString::Bytes(file.as_bytes()))
}
Symbol::Symtab { .. } => None,
}
}
pub fn filename(&self) -> Option<&Path> {
match self {
Symbol::Frame { location, .. } => {
let file = location.as_ref()?.file?;
Some(Path::new(file))
}
Symbol::Symtab { .. } => None,
}
}
pub fn lineno(&self) -> Option<u32> {
match self {
Symbol::Frame { location, .. } => location.as_ref()?.line,
Symbol::Symtab { .. } => None,
}
}
pub fn colno(&self) -> Option<u32> {
match self {
Symbol::Frame { location, .. } => location.as_ref()?.column,
Symbol::Symtab { .. } => None,
}
}
}