FDE finder

.gitignore

@@ -0,0 +1,3 @@
+.vscode/
+target
+Cargo.lock

Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "unwind"
+version = "0.1.0"
+authors = ["Gary Guo <gary@garyguo.net>"]
+edition = "2018"
+
+[dependencies]
+gimli = { version = "0.25.0", default-features = false, features = ["read"] }
+libc = "0.2"
+fallible-iterator = "0.1"
+log = "0.4"
+once_cell = "1.8"
+
+[profile.release]
+debug = true

LICENSE-APACHE

@@ -0,0 +1,176 @@
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+
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+END OF TERMS AND CONDITIONS

LICENSE-MIT

@@ -0,0 +1,23 @@
+Permission is hereby granted, free of charge, to any
+person obtaining a copy of this software and associated
+documentation files (the "Software"), to deal in the
+Software without restriction, including without
+limitation the rights to use, copy, modify, merge,
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+is furnished to do so, subject to the following
+conditions:
+
+The above copyright notice and this permission notice
+shall be included in all copies or substantial portions
+of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
+ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
+TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
+PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
+SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
+IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.

src/find_fde/mod.rs

@@ -0,0 +1,33 @@
+mod phdr;
+mod registry;
+
+use crate::util::*;
+use gimli::{BaseAddresses, EhFrame, FrameDescriptionEntry};
+
+pub struct FDESearchResult {
+    pub fde: FrameDescriptionEntry<StaticSlice>,
+    pub bases: BaseAddresses,
+    pub eh_frame: EhFrame<StaticSlice>,
+}
+
+pub trait FDEFinder {
+    fn find_fde(&self, pc: usize) -> Option<FDESearchResult>;
+}
+
+pub struct GlobalFinder(());
+
+impl FDEFinder for GlobalFinder {
+    fn find_fde(&self, pc: usize) -> Option<FDESearchResult> {
+        if let Some(v) = registry::get_finder().find_fde(pc) {
+            return Some(v);
+        }
+        if let Some(v) = phdr::get_finder().find_fde(pc) {
+            return Some(v);
+        }
+        None
+    }
+}
+
+pub fn get_finder() -> &'static GlobalFinder {
+    &GlobalFinder(())
+}

src/find_fde/phdr.rs

@@ -0,0 +1,130 @@
+use super::FDESearchResult;
+use crate::util::{deref_pointer, get_unlimited_slice};
+use core::mem;
+use core::slice;
+use gimli::{BaseAddresses, EhFrame, EhFrameHdr, NativeEndian, UnwindSection};
+use libc::{c_int, c_void, dl_iterate_phdr, dl_phdr_info, PT_DYNAMIC, PT_GNU_EH_FRAME, PT_LOAD};
+
+struct CallbackData {
+    pc: usize,
+    result: Option<FDESearchResult>,
+}
+
+pub struct PhdrFinder(());
+
+pub fn get_finder() -> &'static PhdrFinder {
+    &PhdrFinder(())
+}
+
+impl super::FDEFinder for PhdrFinder {
+    fn find_fde(&self, pc: usize) -> Option<FDESearchResult> {
+        let mut data = CallbackData { pc, result: None };
+        unsafe { dl_iterate_phdr(Some(phdr_callback), &mut data as *mut CallbackData as _) };
+        data.result
+    }
+}
+
+unsafe extern "C" fn phdr_callback(
+    info: *mut dl_phdr_info,
+    _size: usize,
+    data: *mut c_void,
+) -> c_int {
+    let data = &mut *(data as *mut CallbackData);
+    let phdrs = slice::from_raw_parts((*info).dlpi_phdr, (*info).dlpi_phnum as usize);
+
+    let mut text = None;
+    let mut eh_frame_hdr = None;
+    let mut dynamic = None;
+
+    for phdr in phdrs {
+        let start = (*info).dlpi_addr + phdr.p_vaddr;
+        match phdr.p_type {
+            PT_LOAD => {
+                let end = start + phdr.p_memsz;
+                let range = start..end;
+                if range.contains(&(data.pc as _)) {
+                    text = Some(range);
+                }
+            }
+            PT_GNU_EH_FRAME => {
+                eh_frame_hdr = Some(start);
+            }
+            PT_DYNAMIC => {
+                dynamic = Some(start);
+            }
+            _ => (),
+        }
+    }
+
+    let text = match text {
+        Some(v) => v,
+        None => return 0,
+    };
+
+    let eh_frame_hdr = match eh_frame_hdr {
+        Some(v) => v,
+        None => return 0,
+    };
+
+    let mut bases = BaseAddresses::default()
+        .set_eh_frame_hdr(eh_frame_hdr as _)
+        .set_text(text.start as _);
+
+    // Find the GOT section.
+    if let Some(start) = dynamic {
+        const DT_NULL: usize = 0;
+        const DT_PLTGOT: usize = 3;
+
+        let mut tags = start as *const [usize; 2];
+        let mut tag = *tags;
+        while tag[0] != DT_NULL {
+            if tag[0] == DT_PLTGOT {
+                bases = bases.set_got(tag[1] as _);
+                break;
+            }
+            tags = tags.add(1);
+            tag = *tags;
+        }
+    }
+
+    // Parse .eh_frame_hdr section.
+    let eh_frame_hdr = EhFrameHdr::new(
+        get_unlimited_slice(eh_frame_hdr as usize as _),
+        NativeEndian,
+    )
+    .parse(&bases, mem::size_of::<usize>() as _);
+    let eh_frame_hdr = match eh_frame_hdr {
+        Ok(v) => v,
+        Err(_) => return 0,
+    };
+
+    let eh_frame = deref_pointer(eh_frame_hdr.eh_frame_ptr());
+    bases = bases.set_eh_frame(eh_frame as _);
+    let eh_frame = EhFrame::new(get_unlimited_slice(eh_frame as usize as _), NativeEndian);
+
+    // Use binary search table for address if available.
+    if let Some(table) = eh_frame_hdr.table() {
+        if let Ok(fde) =
+            table.fde_for_address(&eh_frame, &bases, data.pc as _, EhFrame::cie_from_offset)
+        {
+            data.result = Some(FDESearchResult {
+                fde,
+                bases,
+                eh_frame,
+            });
+            return 1;
+        }
+    }
+
+    // Otherwise do the linear search.
+    if let Ok(fde) = eh_frame.fde_for_address(&bases, data.pc as _, EhFrame::cie_from_offset) {
+        data.result = Some(FDESearchResult {
+            fde,
+            bases,
+            eh_frame,
+        });
+        return 1;
+    }
+
+    0
+}

src/find_fde/registry.rs

@@ -0,0 +1,205 @@
+use super::FDESearchResult;
+use crate::util::get_unlimited_slice;
+use core::mem::MaybeUninit;
+use core::ptr;
+use gimli::{BaseAddresses, EhFrame, NativeEndian, UnwindSection};
+use libc::c_void;
+use once_cell::sync::Lazy;
+use std::sync::Mutex;
+
+enum Table {
+    Single(*const c_void),
+    Multiple(*const *const c_void),
+}
+
+struct Object {
+    next: *mut Object,
+    tbase: usize,
+    dbase: usize,
+    table: Table,
+}
+
+struct RegistryInner {
+    object: *mut Object,
+}
+
+unsafe impl Send for RegistryInner {}
+
+pub struct Registry {
+    inner: Mutex<RegistryInner>,
+}
+
+pub fn get_finder() -> &'static Registry {
+    static LAZY: Lazy<Registry> = Lazy::new(|| Registry {
+        inner: Mutex::new(RegistryInner {
+            object: ptr::null_mut(),
+        }),
+    });
+    &*LAZY
+}
+
+impl super::FDEFinder for Registry {
+    fn find_fde(&self, pc: usize) -> Option<FDESearchResult> {
+        let guard = get_finder().inner.lock().unwrap();
+        let mut cur = guard.object;
+
+        unsafe {
+            while !cur.is_null() {
+                let bases = BaseAddresses::default()
+                    .set_text((*cur).tbase as _)
+                    .set_got((*cur).dbase as _);
+                match (*cur).table {
+                    Table::Single(addr) => {
+                        let eh_frame = EhFrame::new(get_unlimited_slice(addr as _), NativeEndian);
+                        let bases = bases.clone().set_eh_frame(addr as usize as _);
+                        if let Ok(fde) =
+                            eh_frame.fde_for_address(&bases, pc as _, EhFrame::cie_from_offset)
+                        {
+                            return Some(FDESearchResult {
+                                fde,
+                                bases,
+                                eh_frame,
+                            });
+                        }
+                    }
+                    Table::Multiple(mut addrs) => {
+                        let mut addr = *addrs;
+                        while !addr.is_null() {
+                            let eh_frame =
+                                EhFrame::new(get_unlimited_slice(addr as _), NativeEndian);
+                            let bases = bases.clone().set_eh_frame(addr as usize as _);
+                            if let Ok(fde) =
+                                eh_frame.fde_for_address(&bases, pc as _, EhFrame::cie_from_offset)
+                            {
+                                return Some(FDESearchResult {
+                                    fde,
+                                    bases,
+                                    eh_frame,
+                                });
+                            }
+
+                            addrs = addrs.add(1);
+                            addr = *addrs;
+                        }
+                    }
+                }
+
+                cur = (*cur).next;
+            }
+        }
+
+        None
+    }
+}
+
+#[no_mangle]
+unsafe extern "C" fn __register_frame_info_bases(
+    begin: *const c_void,
+    ob: *mut Object,
+    tbase: *const c_void,
+    dbase: *const c_void,
+) {
+    if begin.is_null() {
+        return;
+    }
+
+    ob.write(Object {
+        next: core::ptr::null_mut(),
+        tbase: tbase as _,
+        dbase: dbase as _,
+        table: Table::Single(begin),
+    });
+
+    let mut guard = get_finder().inner.lock().unwrap();
+    (*ob).next = guard.object;
+    guard.object = ob;
+}
+
+#[no_mangle]
+unsafe extern "C" fn __register_frame_info(begin: *const c_void, ob: *mut Object) {
+    __register_frame_info_bases(begin, ob, core::ptr::null_mut(), core::ptr::null_mut());
+}
+
+#[no_mangle]
+unsafe extern "C" fn __register_frame(begin: *const c_void) {
+    if begin.is_null() {
+        return;
+    }
+
+    let storage = Box::into_raw(Box::new(MaybeUninit::<Object>::uninit())) as *mut Object;
+    __register_frame_info(begin, storage);
+}
+
+#[no_mangle]
+unsafe extern "C" fn __register_frame_info_table_bases(
+    begin: *const c_void,
+    ob: *mut Object,
+    tbase: *const c_void,
+    dbase: *const c_void,
+) {
+    ob.write(Object {
+        next: core::ptr::null_mut(),
+        tbase: tbase as _,
+        dbase: dbase as _,
+        table: Table::Multiple(begin as _),
+    });
+
+    let mut guard = get_finder().inner.lock().unwrap();
+    (*ob).next = guard.object;
+    guard.object = ob;
+}
+
+#[no_mangle]
+unsafe extern "C" fn __register_frame_info_table(begin: *const c_void, ob: *mut Object) {
+    __register_frame_info_table_bases(begin, ob, core::ptr::null_mut(), core::ptr::null_mut());
+}
+
+#[no_mangle]
+unsafe extern "C" fn __register_frame_table(begin: *const c_void) {
+    if begin.is_null() {
+        return;
+    }
+
+    let storage = Box::into_raw(Box::new(MaybeUninit::<Object>::uninit())) as *mut Object;
+    __register_frame_info_table(begin, storage);
+}
+
+#[no_mangle]
+unsafe extern "C" fn __deregister_frame_info_bases(begin: *const c_void) -> *mut Object {
+    if begin.is_null() {
+        return core::ptr::null_mut();
+    }
+
+    let mut guard = get_finder().inner.lock().unwrap();
+    let mut prev = &mut guard.object;
+    let mut cur = *prev;
+
+    while !cur.is_null() {
+        let found = match (*cur).table {
+            Table::Single(addr) => addr == begin,
+            _ => false,
+        };
+        if found {
+            *prev = (*cur).next;
+            return cur;
+        }
+        prev = &mut (*cur).next;
+        cur = *prev;
+    }
+
+    core::ptr::null_mut()
+}
+
+#[no_mangle]
+unsafe extern "C" fn __deregister_frame_info(begin: *const c_void) -> *mut Object {
+    __deregister_frame_info_bases(begin)
+}
+
+#[no_mangle]
+unsafe extern "C" fn __deregister_frame(begin: *const c_void) {
+    if begin.is_null() {
+        return;
+    }
+    let storage = __deregister_frame_info(begin);
+    drop(Box::from_raw(storage as *mut MaybeUninit<Object>))
+}

src/lib.rs

@@ -0,0 +1,2 @@
+mod find_fde;
+mod util;

src/util.rs

@@ -0,0 +1,18 @@
+use gimli::{EndianSlice, NativeEndian, Pointer};
+
+pub type StaticSlice = EndianSlice<'static, NativeEndian>;
+
+pub unsafe fn get_unlimited_slice<'a>(start: *const u8) -> &'a [u8] {
+    // Create the largest possible slice for this address.
+    let start = start as usize;
+    let end = start.saturating_add(isize::MAX as _);
+    let len = end - start;
+    core::slice::from_raw_parts(start as *const _, len)
+}
+
+pub unsafe fn deref_pointer(ptr: Pointer) -> usize {
+    match ptr {
+        Pointer::Direct(x) => x as _,
+        Pointer::Indirect(x) => *(x as *const _),
+    }
+}