src/libpanic_unwind/dwarf/eh.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! Parsing of GCC-style Language-Specific Data Area (LSDA)
  12 //! For details see:
  13 //!   http://refspecs.linuxfoundation.org/LSB_3.0.0/LSB-PDA/LSB-PDA/ehframechpt.html
  14 //!   http://mentorembedded.github.io/cxx-abi/exceptions.pdf
  15 //!   http://www.airs.com/blog/archives/460
  16 //!   http://www.airs.com/blog/archives/464
  17 //!
  18 //! A reference implementation may be found in the GCC source tree
  19 //! (<root>/libgcc/unwind-c.c as of this writing)
  20
  21 #![allow(non_upper_case_globals)]
  22 #![allow(unused)]
  23
  24 use dwarf::DwarfReader;
  25 use core::mem;
  26
  27 pub const DW_EH_PE_omit: u8 = 0xFF;
  28 pub const DW_EH_PE_absptr: u8 = 0x00;
  29
  30 pub const DW_EH_PE_uleb128: u8 = 0x01;
  31 pub const DW_EH_PE_udata2: u8 = 0x02;
  32 pub const DW_EH_PE_udata4: u8 = 0x03;
  33 pub const DW_EH_PE_udata8: u8 = 0x04;
  34 pub const DW_EH_PE_sleb128: u8 = 0x09;
  35 pub const DW_EH_PE_sdata2: u8 = 0x0A;
  36 pub const DW_EH_PE_sdata4: u8 = 0x0B;
  37 pub const DW_EH_PE_sdata8: u8 = 0x0C;
  38
  39 pub const DW_EH_PE_pcrel: u8 = 0x10;
  40 pub const DW_EH_PE_textrel: u8 = 0x20;
  41 pub const DW_EH_PE_datarel: u8 = 0x30;
  42 pub const DW_EH_PE_funcrel: u8 = 0x40;
  43 pub const DW_EH_PE_aligned: u8 = 0x50;
  44
  45 pub const DW_EH_PE_indirect: u8 = 0x80;
  46
  47 #[derive(Copy, Clone)]
  48 pub struct EHContext<'a> {
  49     pub ip: usize, // Current instruction pointer
  50     pub func_start: usize, // Address of the current function
  51     pub get_text_start: &'a Fn() -> usize, // Get address of the code section
  52     pub get_data_start: &'a Fn() -> usize, // Get address of the data section
  53 }
  54
  55 pub enum EHAction {
  56     None,
  57     Cleanup(usize),
  58     Catch(usize),
  59     Terminate,
  60 }
  61
  62 pub const USING_SJLJ_EXCEPTIONS: bool = cfg!(all(target_os = "ios", target_arch = "arm"));
  63
  64 pub unsafe fn find_eh_action(lsda: *const u8, context: &EHContext) -> EHAction {
  65     if lsda.is_null() {
  66         return EHAction::None;
  67     }
  68
  69     let func_start = context.func_start;
  70     let mut reader = DwarfReader::new(lsda);
  71
  72     let start_encoding = reader.read::<u8>();
  73     // base address for landing pad offsets
  74     let lpad_base = if start_encoding != DW_EH_PE_omit {
  75         read_encoded_pointer(&mut reader, context, start_encoding)
  76     } else {
  77         func_start
  78     };
  79
  80     let ttype_encoding = reader.read::<u8>();
  81     if ttype_encoding != DW_EH_PE_omit {
  82         // Rust doesn't analyze exception types, so we don't care about the type table
  83         reader.read_uleb128();
  84     }
  85
  86     let call_site_encoding = reader.read::<u8>();
  87     let call_site_table_length = reader.read_uleb128();
  88     let action_table = reader.ptr.offset(call_site_table_length as isize);
  89     let ip = context.ip;
  90
  91     if !USING_SJLJ_EXCEPTIONS {
  92         while reader.ptr < action_table {
  93             let cs_start = read_encoded_pointer(&mut reader, context, call_site_encoding);
  94             let cs_len = read_encoded_pointer(&mut reader, context, call_site_encoding);
  95             let cs_lpad = read_encoded_pointer(&mut reader, context, call_site_encoding);
  96             let cs_action = reader.read_uleb128();
  97             // Callsite table is sorted by cs_start, so if we've passed the ip, we
  98             // may stop searching.
  99             if ip < func_start + cs_start {
 100                 break;
 101             }
 102             if ip < func_start + cs_start + cs_len {
 103                 if cs_lpad == 0 {
 104                     return EHAction::None;
 105                 } else {
 106                     let lpad = lpad_base + cs_lpad;
 107                     return interpret_cs_action(cs_action, lpad);
 108                 }
 109             }
 110         }
 111         // Ip is not present in the table.  This should not happen... but it does: issue #35011.
 112         // So rather than returning EHAction::Terminate, we do this.
 113         EHAction::None
 114     } else {
 115         // SjLj version:
 116         // The "IP" is an index into the call-site table, with two exceptions:
 117         // -1 means 'no-action', and 0 means 'terminate'.
 118         match ip as isize {
 119            -1 => return EHAction::None,
 120             0 => return EHAction::Terminate,
 121             _ => (),
 122         }
 123         let mut idx = ip;
 124         loop {
 125             let cs_lpad = reader.read_uleb128();
 126             let cs_action = reader.read_uleb128();
 127             idx -= 1;
 128             if idx == 0 {
 129                 // Can never have null landing pad for sjlj -- that would have
 130                 // been indicated by a -1 call site index.
 131                 let lpad = (cs_lpad + 1) as usize;
 132                 return interpret_cs_action(cs_action, lpad);
 133             }
 134         }
 135     }
 136 }
 137
 138 fn interpret_cs_action(cs_action: u64, lpad: usize) -> EHAction {
 139     if cs_action == 0 {
 140         EHAction::Cleanup(lpad)
 141     } else {
 142         EHAction::Catch(lpad)
 143     }
 144 }
 145
 146 #[inline]
 147 fn round_up(unrounded: usize, align: usize) -> usize {
 148     assert!(align.is_power_of_two());
 149     (unrounded + align - 1) & !(align - 1)
 150 }
 151
 152 unsafe fn read_encoded_pointer(reader: &mut DwarfReader,
 153                                context: &EHContext,
 154                                encoding: u8)
 155                                -> usize {
 156     assert!(encoding != DW_EH_PE_omit);
 157
 158     // DW_EH_PE_aligned implies it's an absolute pointer value
 159     if encoding == DW_EH_PE_aligned {
 160         reader.ptr = round_up(reader.ptr as usize, mem::size_of::<usize>()) as *const u8;
 161         return reader.read::<usize>();
 162     }
 163
 164     let mut result = match encoding & 0x0F {
 165         DW_EH_PE_absptr => reader.read::<usize>(),
 166         DW_EH_PE_uleb128 => reader.read_uleb128() as usize,
 167         DW_EH_PE_udata2 => reader.read::<u16>() as usize,
 168         DW_EH_PE_udata4 => reader.read::<u32>() as usize,
 169         DW_EH_PE_udata8 => reader.read::<u64>() as usize,
 170         DW_EH_PE_sleb128 => reader.read_sleb128() as usize,
 171         DW_EH_PE_sdata2 => reader.read::<i16>() as usize,
 172         DW_EH_PE_sdata4 => reader.read::<i32>() as usize,
 173         DW_EH_PE_sdata8 => reader.read::<i64>() as usize,
 174         _ => panic!(),
 175     };
 176
 177     result += match encoding & 0x70 {
 178         DW_EH_PE_absptr => 0,
 179         // relative to address of the encoded value, despite the name
 180         DW_EH_PE_pcrel => reader.ptr as usize,
 181         DW_EH_PE_funcrel => {
 182             assert!(context.func_start != 0);
 183             context.func_start
 184         }
 185         DW_EH_PE_textrel => {
 186             (*context.get_text_start)()
 187         }
 188         DW_EH_PE_datarel => {
 189             (*context.get_data_start)()
 190         }
 191         _ => panic!(),
 192     };
 193
 194     if encoding & DW_EH_PE_indirect != 0 {
 195         result = *(result as *const usize);
 196     }
 197
 198     result
 199 }