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// Copyright 2014-2015 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. // // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your // option. This file may not be copied, modified, or distributed // except according to those terms. //! Symbolication strategy using the DWARF-parsing code in libbacktrace. //! //! The libbacktrace C library, typically distributed with gcc, supports not //! only generating a backtrace (which we don't actually use) but also //! symbolicating the backtrace and handling dwarf debug information about //! things like inlined frames and whatnot. //! //! This is relatively complicated due to lots of various concerns here, but the //! basic idea is: //! //! * First we call `backtrace_syminfo`. This gets symbol information from the //! dynamic symbol table if we can. //! * Next we call `backtrace_pcinfo`. This will parse debuginfo tables if //! they're available and allow us to recover information about inline frames, //! filenames, line numbers, etc. //! //! There's lots of trickery about getting the dwarf tables into libbacktrace, //! but hopefully it's not the end of the world and is clear enough when reading //! below. //! //! This is the default symbolication strategy for non-MSVC and non-OSX //! platforms. In libstd though this is the default strategy for OSX. #![allow(bad_style)] extern crate backtrace_sys as bt; use core::{ptr, slice}; use libc::{self, c_char, c_int, c_void, uintptr_t}; use crate::symbolize::dladdr; use crate::symbolize::{ResolveWhat, SymbolName}; use crate::types::BytesOrWideString; pub enum Symbol<'a> { Syminfo { pc: uintptr_t, symname: *const c_char, }, Pcinfo { pc: uintptr_t, filename: *const c_char, lineno: c_int, function: *const c_char, symname: *const c_char, }, Dladdr(dladdr::Symbol<'a>), } impl Symbol<'_> { pub fn name(&self) -> Option<SymbolName> { let symbol = |ptr: *const c_char| unsafe { if ptr.is_null() { None } else { let len = libc::strlen(ptr); Some(SymbolName::new(slice::from_raw_parts( ptr as *const u8, len, ))) } }; match *self { Symbol::Syminfo { symname, .. } => symbol(symname), Symbol::Pcinfo { function, symname, .. } => { // If possible prefer the `function` name which comes from // debuginfo and can typically be more accurate for inline // frames for example. If that's not present though fall back to // the symbol table name specified in `symname`. // // Note that sometimes `function` can feel somewhat less // accurate, for example being listed as `try<i32,closure>` // isntead of `std::panicking::try::do_call`. It's not really // clear why, but overall the `function` name seems more accurate. if let Some(sym) = symbol(function) { return Some(sym); } symbol(symname) } Symbol::Dladdr(ref s) => s.name(), } } pub fn addr(&self) -> Option<*mut c_void> { let pc = match *self { Symbol::Syminfo { pc, .. } => pc, Symbol::Pcinfo { pc, .. } => pc, Symbol::Dladdr(ref s) => return s.addr(), }; if pc == 0 { None } else { Some(pc as *mut _) } } fn filename_bytes(&self) -> Option<&[u8]> { match *self { Symbol::Syminfo { .. } => None, Symbol::Pcinfo { filename, .. } => { let ptr = filename as *const u8; unsafe { let len = libc::strlen(filename); Some(slice::from_raw_parts(ptr, len)) } } Symbol::Dladdr(_) => None, } } pub fn filename_raw(&self) -> Option<BytesOrWideString> { self.filename_bytes().map(BytesOrWideString::Bytes) } #[cfg(feature = "std")] pub fn filename(&self) -> Option<&::std::path::Path> { use std::path::Path; #[cfg(unix)] fn bytes2path(bytes: &[u8]) -> Option<&Path> { use std::ffi::OsStr; use std::os::unix::prelude::*; Some(Path::new(OsStr::from_bytes(bytes))) } #[cfg(windows)] fn bytes2path(bytes: &[u8]) -> Option<&Path> { use std::str; str::from_utf8(bytes).ok().map(Path::new) } self.filename_bytes().and_then(bytes2path) } pub fn lineno(&self) -> Option<u32> { match *self { Symbol::Syminfo { .. } => None, Symbol::Pcinfo { lineno, .. } => Some(lineno as u32), Symbol::Dladdr(ref s) => s.lineno(), } } } extern "C" fn error_cb(_data: *mut c_void, _msg: *const c_char, _errnum: c_int) { // do nothing for now } /// Type of the `data` pointer passed into `syminfo_cb` struct SyminfoState<'a> { cb: &'a mut (FnMut(&super::Symbol) + 'a), pc: usize, } extern "C" fn syminfo_cb( data: *mut c_void, pc: uintptr_t, symname: *const c_char, _symval: uintptr_t, _symsize: uintptr_t, ) { let mut bomb = crate::Bomb { enabled: true }; // Once this callback is invoked from `backtrace_syminfo` when we start // resolving we go further to call `backtrace_pcinfo`. The // `backtrace_pcinfo` function will consult debug information and attemp tto // do things like recover file/line information as well as inlined frames. // Note though that `backtrace_pcinfo` can fail or not do much if there's // not debug info, so if that happens we're sure to call the callback with // at least one symbol from the `syminfo_cb`. unsafe { let syminfo_state = &mut *(data as *mut SyminfoState); let mut pcinfo_state = PcinfoState { symname, called: false, cb: syminfo_state.cb, }; bt::backtrace_pcinfo( init_state(), syminfo_state.pc as uintptr_t, pcinfo_cb, error_cb, &mut pcinfo_state as *mut _ as *mut _, ); if !pcinfo_state.called { (pcinfo_state.cb)(&super::Symbol { inner: Symbol::Syminfo { pc: pc, symname: symname, }, }); } } bomb.enabled = false; } /// Type of the `data` pointer passed into `pcinfo_cb` struct PcinfoState<'a> { cb: &'a mut (FnMut(&super::Symbol) + 'a), symname: *const c_char, called: bool, } extern "C" fn pcinfo_cb( data: *mut c_void, pc: uintptr_t, filename: *const c_char, lineno: c_int, function: *const c_char, ) -> c_int { if filename.is_null() || function.is_null() { return -1; } let mut bomb = crate::Bomb { enabled: true }; unsafe { let state = &mut *(data as *mut PcinfoState); state.called = true; (state.cb)(&super::Symbol { inner: Symbol::Pcinfo { pc: pc, filename: filename, lineno: lineno, symname: state.symname, function, }, }); } bomb.enabled = false; return 0; } // The libbacktrace API supports creating a state, but it does not // support destroying a state. I personally take this to mean that a // state is meant to be created and then live forever. // // I would love to register an at_exit() handler which cleans up this // state, but libbacktrace provides no way to do so. // // With these constraints, this function has a statically cached state // that is calculated the first time this is requested. Remember that // backtracing all happens serially (one global lock). // // Note the lack of synchronization here is due to the requirement that // `resolve` is externally synchronized. unsafe fn init_state() -> *mut bt::backtrace_state { static mut STATE: *mut bt::backtrace_state = 0 as *mut _; if !STATE.is_null() { return STATE; } STATE = bt::backtrace_create_state( load_filename(), // Don't exercise threadsafe capabilities of libbacktrace since // we're always calling it in a synchronized fashion. 0, error_cb, ptr::null_mut(), // no extra data ); return STATE; // Note that for libbacktrace to operate at all it needs to find the DWARF // debug info for the current executable. It typically does that via a // number of mechanisms including, but not limited to: // // * /proc/self/exe on supported platforms // * The filename passed in explicitly when creating state // // The libbacktrace library is a big wad of C code. This naturally means // it's got memory safety vulnerabilities, especially when handling // malformed debuginfo. Libstd has run into plenty of these historically. // // If /proc/self/exe is used then we can typically ignore these as we // assume that libbacktrace is "mostly correct" and otherwise doesn't do // weird things with "attempted to be correct" dwarf debug info. // // If we pass in a filename, however, then it's possible on some platforms // (like BSDs) where a malicious actor can cause an arbitrary file to be // placed at that location. This means that if we tell libbacktrace about a // filename it may be using an arbitrary file, possibly causing segfaults. // If we don't tell libbacktrace anything though then it won't do anything // on platforms that don't support paths like /proc/self/exe! // // Given all that we try as hard as possible to *not* pass in a filename, // but we must on platforms that don't support /proc/self/exe at all. cfg_if::cfg_if! { if #[cfg(any(target_os = "macos", target_os = "ios"))] { // Note that ideally we'd use `std::env::current_exe`, but we can't // require `std` here. // // Use `_NSGetExecutablePath` to load the current executable path // into a static area (which if it's too small just give up). // // Note that we're seriously trusting libbacktrace here to not die // on corrupt executables, but it surely does... unsafe fn load_filename() -> *const libc::c_char { const N: usize = 256; static mut BUF: [u8; N] = [0; N]; extern { fn _NSGetExecutablePath( buf: *mut libc::c_char, bufsize: *mut u32, ) -> libc::c_int; } let mut sz: u32 = BUF.len() as u32; let ptr = BUF.as_mut_ptr() as *mut libc::c_char; if _NSGetExecutablePath(ptr, &mut sz) == 0 { ptr } else { ptr::null() } } } else if #[cfg(windows)] { use crate::windows::*; // Windows has a mode of opening files where after it's opened it // can't be deleted. That's in general what we want here because we // want to ensure that our executable isn't changing out from under // us after we hand it off to libbacktrace, hopefully mitigating the // ability to pass in arbitrary data into libbacktrace (which may be // mishandled). // // Given that we do a bit of a dance here to attempt to get a sort // of lock on our own image: // // * Get a handle to the current process, load its filename. // * Open a file to that filename with the right flags. // * Reload the current process's filename, making sure it's the same // // If that all passes we in theory have indeed opened our process's // file and we're guaranteed it won't change. FWIW a bunch of this // is copied from libstd historically, so this is my best // interpretation of what was happening. unsafe fn load_filename() -> *const libc::c_char { load_filename_opt().unwrap_or(ptr::null()) } unsafe fn load_filename_opt() -> Result<*const libc::c_char, ()> { const N: usize = 256; // This lives in static memory so we can return it.. static mut BUF: [i8; N] = [0; N]; // ... and this lives on the stack since it's temporary let mut stack_buf = [0; N]; let name1 = query_full_name(&mut BUF)?; let handle = CreateFileA( name1.as_ptr(), GENERIC_READ, FILE_SHARE_READ | FILE_SHARE_WRITE, ptr::null_mut(), OPEN_EXISTING, 0, ptr::null_mut(), ); if handle.is_null() { return Err(()); } let name2 = query_full_name(&mut stack_buf)?; if name1 != name2 { CloseHandle(handle); return Err(()) } // intentionally leak `handle` here because having that open // should preserve our lock on this file name. Ok(name1.as_ptr()) } unsafe fn query_full_name(buf: &mut [i8]) -> Result<&[i8], ()> { let dll = GetModuleHandleA(b"kernel32.dll\0".as_ptr() as *const i8); if dll.is_null() { return Err(()) } let ptrQueryFullProcessImageNameA = GetProcAddress(dll, b"QueryFullProcessImageNameA\0".as_ptr() as *const _) as usize; if ptrQueryFullProcessImageNameA == 0 { return Err(()); } use core::mem; let p1 = OpenProcess(PROCESS_QUERY_INFORMATION, FALSE, GetCurrentProcessId()); let mut len = buf.len() as u32; let pfnQueryFullProcessImageNameA : extern "system" fn( hProcess: HANDLE, dwFlags: DWORD, lpExeName: LPSTR, lpdwSize: PDWORD, ) -> BOOL = mem::transmute(ptrQueryFullProcessImageNameA); let rc = pfnQueryFullProcessImageNameA(p1, 0, buf.as_mut_ptr(), &mut len); CloseHandle(p1); // We want to return a slice that is nul-terminated, so if // everything was filled in and it equals the total length // then equate that to failure. // // Otherwise when returning success make sure the nul byte is // included in the slice. if rc == 0 || len == buf.len() as u32 { Err(()) } else { assert_eq!(buf[len as usize], 0); Ok(&buf[..(len + 1) as usize]) } } } else if #[cfg(target_os = "vxworks")] { unsafe fn load_filename() -> *const libc::c_char { use libc; use core::mem; const N: usize = libc::VX_RTP_NAME_LENGTH as usize + 1; static mut BUF: [libc::c_char; N] = [0; N]; let mut rtp_desc : libc::RTP_DESC = mem::zeroed(); if (libc::rtpInfoGet(0, &mut rtp_desc as *mut libc::RTP_DESC) == 0) { BUF.copy_from_slice(&rtp_desc.pathName); BUF.as_ptr() } else { ptr::null() } } } else { unsafe fn load_filename() -> *const libc::c_char { ptr::null() } } } } pub unsafe fn resolve(what: ResolveWhat, cb: &mut FnMut(&super::Symbol)) { let symaddr = what.address_or_ip() as usize; // backtrace errors are currently swept under the rug let state = init_state(); if state.is_null() { return dladdr_fallback(what.address_or_ip(), cb); } // Call the `backtrace_syminfo` API first. This is (from reading the code) // guaranteed to call `syminfo_cb` exactly once (or fail with an error // presumably). We then handle more within the `syminfo_cb`. // // Note that we do this since `syminfo` will consult the symbol table, // finding symbol names even if there's no debug information in the binary. let mut called = false; { let mut syminfo_state = SyminfoState { pc: symaddr, cb: &mut |sym| { called = true; cb(sym); }, }; bt::backtrace_syminfo( state, symaddr as uintptr_t, syminfo_cb, error_cb, &mut syminfo_state as *mut _ as *mut _, ); } if !called { dladdr_fallback(what.address_or_ip(), cb); } } unsafe fn dladdr_fallback(addr: *mut c_void, cb: &mut FnMut(&super::Symbol)) { dladdr::resolve(addr, &mut |sym| { cb(&super::Symbol { inner: Symbol::Dladdr(sym), }) }); }