backtrace/symbolize/

gimli.rs

//! 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 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(target_vendor = "apple")] {
        #[path = "gimli/mmap_unix.rs"]
        mod mmap;
    } else if #[cfg(any(
        target_os = "android",
        target_os = "freebsd",
        target_os = "fuchsia",
        target_os = "haiku",
        target_os = "hurd",
        target_os = "linux",
        target_os = "openbsd",
        target_os = "solaris",
        target_os = "illumos",
        target_os = "aix",
        target_os = "cygwin",
    ))] {
        #[path = "gimli/mmap_unix.rs"]
        mod mmap;
    } else {
        #[path = "gimli/mmap_fake.rs"]
        mod mmap;
    }
}

mod lru;
mod stash;

use lru::Lru;

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,
        })
    }
}

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<_, ()> {
            if cfg!(not(target_os = "aix")) {
                let data = object.section(stash, id.name()).unwrap_or(&[]);
                Ok(EndianSlice::new(data, Endian))
            } else if let Some(name) = id.xcoff_name() {
                let data = object.section(stash, name).unwrap_or(&[]);
                Ok(EndianSlice::new(data, Endian))
            } else {
                Ok(EndianSlice::new(&[], 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, 0) }
}

cfg_if::cfg_if! {
    if #[cfg(any(windows, target_os = "cygwin"))] {
        mod coff;
        use self::coff::{handle_split_dwarf, Object};
    } else if #[cfg(any(target_vendor = "apple"))] {
        mod macho;
        use self::macho::{handle_split_dwarf, Object};
    } else if #[cfg(target_os = "aix")] {
        mod xcoff;
        use self::xcoff::{handle_split_dwarf, Object};
    } else {
        mod elf;
        use self::elf::{handle_split_dwarf, Object};
    }
}

cfg_if::cfg_if! {
    if #[cfg(any(windows, target_os = "cygwin"))] {
        mod libs_windows;
        use libs_windows::native_libraries;
    } else if #[cfg(target_vendor = "apple")] {
        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 = "hurd",
            target_os = "openbsd",
            target_os = "netbsd",
            target_os = "nto",
            target_os = "android",
        ),
        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 if #[cfg(target_os = "aix")] {
        mod libs_aix;
        use libs_aix::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: Lru<(usize, Mapping), MAPPINGS_CACHE_SIZE>,
}

struct Library {
    name: OsString,
    #[cfg(target_os = "android")]
    /// On Android, the dynamic linker [can map libraries directly from a
    /// ZIP archive][ndk-linker-changes] (typically an `.apk`).
    ///
    /// The linker requires that these libraries are stored uncompressed
    /// and page-aligned.
    ///
    /// These "embedded" libraries have filepaths of the form
    /// `/path/to/my.apk!/lib/mylib.so` (where `/path/to/my.apk` is the archive
    /// and `lib/mylib.so` is the name of the library within the archive).
    ///
    /// This mechanism is present on Android since API level 23.
    ///
    /// [ndk-linker-changes]: https://android.googlesource.com/platform/bionic/+/main/android-changes-for-ndk-developers.md#opening-shared-libraries-directly-from-an-apk
    zip_offset: Option<u64>,
    #[cfg(target_os = "aix")]
    /// On AIX, the library mmapped can be a member of a big-archive file.
    /// For example, with a big-archive named libfoo.a containing libbar.so,
    /// one can use `dlopen("libfoo.a(libbar.so)", RTLD_MEMBER | RTLD_LAZY)`
    /// to use the `libbar.so` library. In this case, only `libbar.so` is
    /// mmapped, not the whole `libfoo.a`.
    member_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,
}

fn create_mapping(lib: &Library) -> Option<Mapping> {
    cfg_if::cfg_if! {
        if #[cfg(target_os = "aix")] {
            Mapping::new(lib.name.as_ref(), &lib.member_name)
        } else if #[cfg(target_os = "android")] {
            Mapping::new_android(lib.name.as_ref(), lib.zip_offset)
        } else {
            Mapping::new(lib.name.as_ref())
        }
    }
}

/// Try to extract the archive path from an "embedded" library path
/// (e.g. `/path/to/my.apk` from `/path/to/my.apk!/mylib.so`).
///
/// Returns `None` if the path does not contain a `!/` separator.
#[cfg(target_os = "android")]
fn extract_zip_path_android(path: &mystd::ffi::OsStr) -> Option<&mystd::ffi::OsStr> {
    use mystd::os::unix::ffi::OsStrExt;

    path.as_bytes()
        .windows(2)
        .enumerate()
        .find(|(_, chunk)| chunk == b"!/")
        .map(|(index, _)| mystd::ffi::OsStr::from_bytes(path.as_bytes().split_at(index).0))
}

// unsafe because this is required to be externally synchronized
pub unsafe fn clear_symbol_cache() {
    unsafe {
        Cache::with_global(|cache| cache.mappings.clear());
    }
}

impl Cache {
    fn new() -> Cache {
        Cache {
            mappings: Lru::default(),
            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;

        unsafe {
            // FIXME: https://github.com/rust-lang/backtrace-rs/issues/678
            #[allow(static_mut_refs)]
            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 cache_idx = self.mappings.iter().position(|(lib_id, _)| *lib_id == lib);

        let cache_entry = if let Some(idx) = cache_idx {
            self.mappings.move_to_front(idx)
        } else {
            // When the mapping is not in the cache, create a new mapping and insert it,
            // which will also evict the oldest entry.
            create_mapping(&self.libraries[lib])
                .and_then(|mapping| self.mappings.push_front((lib, mapping)))
        };

        let (_, mapping) = cache_entry?;
        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.
        // SAFETY: praying the above is correct
        let sym = unsafe { mem::transmute::<Symbol<'_>, Symbol<'static>>(sym) };
        (cb)(&super::Symbol { inner: sym });
    };

    unsafe {
        Cache::with_global(|cache| {
            let (lib, addr) = match cache.avma_to_svma(addr.cast_const().cast::<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 { 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 { 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,
        }
    }
}