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    // Copyright 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.

    //! Parsing of GCC-style Language-Specific Data Area (LSDA)
    //! For details see:
    //!   http://refspecs.linuxfoundation.org/LSB_3.0.0/LSB-PDA/LSB-PDA/ehframechpt.html
    //!   http://mentorembedded.github.io/cxx-abi/exceptions.pdf
    //!   http://www.airs.com/blog/archives/460
    //!   http://www.airs.com/blog/archives/464
    //!
    //! A reference implementation may be found in the GCC source tree
    //! (<root>/libgcc/unwind-c.c as of this writing)

    #![allow(non_upper_case_globals)]
    #![allow(unused)]

    use prelude::v1::*;
    use sys_common::dwarf::DwarfReader;
    use core::mem;

    pub const DW_EH_PE_omit     : u8 = 0xFF;
    pub const DW_EH_PE_absptr   : u8 = 0x00;

    pub const DW_EH_PE_uleb128  : u8 = 0x01;
    pub const DW_EH_PE_udata2   : u8 = 0x02;
    pub const DW_EH_PE_udata4   : u8 = 0x03;
    pub const DW_EH_PE_udata8   : u8 = 0x04;
    pub const DW_EH_PE_sleb128  : u8 = 0x09;
    pub const DW_EH_PE_sdata2   : u8 = 0x0A;
    pub const DW_EH_PE_sdata4   : u8 = 0x0B;
    pub const DW_EH_PE_sdata8   : u8 = 0x0C;

    pub const DW_EH_PE_pcrel    : u8 = 0x10;
    pub const DW_EH_PE_textrel  : u8 = 0x20;
    pub const DW_EH_PE_datarel  : u8 = 0x30;
    pub const DW_EH_PE_funcrel  : u8 = 0x40;
    pub const DW_EH_PE_aligned  : u8 = 0x50;

    pub const DW_EH_PE_indirect : u8 = 0x80;

    #[derive(Copy, Clone)]
    pub struct EHContext {
        pub ip: usize,         // Current instruction pointer
        pub func_start: usize, // Address of the current function
        pub text_start: usize, // Address of the code section
        pub data_start: usize, // Address of the data section
    }

    pub unsafe fn find_landing_pad(lsda: *const u8, context: &EHContext)
                                   -> Option<usize> {
        if lsda.is_null() {
            return None;
        }

        let func_start = context.func_start;
        let mut reader = DwarfReader::new(lsda);

        let start_encoding = reader.read::<u8>();
        // base address for landing pad offsets
        let lpad_base = if start_encoding != DW_EH_PE_omit {
            read_encoded_pointer(&mut reader, context, start_encoding)
        } else {
            func_start
        };

        let ttype_encoding = reader.read::<u8>();
        if ttype_encoding != DW_EH_PE_omit {
            // Rust doesn't analyze exception types, so we don't care about the type table
            reader.read_uleb128();
        }

        let call_site_encoding = reader.read::<u8>();
        let call_site_table_length = reader.read_uleb128();
        let action_table = reader.ptr.offset(call_site_table_length as isize);
        // Return addresses point 1 byte past the call instruction, which could
        // be in the next IP range.
        let ip = context.ip-1;

        while reader.ptr < action_table {
            let cs_start = read_encoded_pointer(&mut reader, context, call_site_encoding);
            let cs_len = read_encoded_pointer(&mut reader, context, call_site_encoding);
            let cs_lpad = read_encoded_pointer(&mut reader, context, call_site_encoding);
            let cs_action = reader.read_uleb128();
            // Callsite table is sorted by cs_start, so if we've passed the ip, we
            // may stop searching.
            if ip < func_start + cs_start {
                break
            }
            if ip < func_start + cs_start + cs_len {
                if cs_lpad != 0 {
                    return Some(lpad_base + cs_lpad);
                } else {
                    return None;
                }
            }
        }
        // IP range not found: gcc's C++ personality calls terminate() here,
        // however the rest of the languages treat this the same as cs_lpad == 0.
        // We follow this suit.
        None
    }

    #[inline]
    fn round_up(unrounded: usize, align: usize) -> usize {
        assert!(align.is_power_of_two());
        (unrounded + align - 1) & !(align - 1)
    }

    unsafe fn read_encoded_pointer(reader: &mut DwarfReader,
                                   context: &EHContext,
                                   encoding: u8) -> usize {
        assert!(encoding != DW_EH_PE_omit);

        // DW_EH_PE_aligned implies it's an absolute pointer value
        if encoding == DW_EH_PE_aligned {
            reader.ptr = round_up(reader.ptr as usize,
                                  mem::size_of::<usize>()) as *const u8;
            return reader.read::<usize>();
        }

        let mut result = match encoding & 0x0F {
            DW_EH_PE_absptr => reader.read::<usize>(),
            DW_EH_PE_uleb128 => reader.read_uleb128() as usize,
            DW_EH_PE_udata2 => reader.read::<u16>() as usize,
            DW_EH_PE_udata4 => reader.read::<u32>() as usize,
            DW_EH_PE_udata8 => reader.read::<u64>() as usize,
            DW_EH_PE_sleb128 => reader.read_sleb128() as usize,
            DW_EH_PE_sdata2 => reader.read::<i16>() as usize,
            DW_EH_PE_sdata4 => reader.read::<i32>() as usize,
            DW_EH_PE_sdata8 => reader.read::<i64>() as usize,
            _ => panic!()
        };

        result += match encoding & 0x70 {
            DW_EH_PE_absptr => 0,
            // relative to address of the encoded value, despite the name
            DW_EH_PE_pcrel => reader.ptr as usize,
            DW_EH_PE_textrel => { assert!(context.text_start != 0);
                                  context.text_start },
            DW_EH_PE_datarel => { assert!(context.data_start != 0);
                                  context.data_start },
            DW_EH_PE_funcrel => { assert!(context.func_start != 0);
                                  context.func_start },
            _ => panic!()
        };

        if encoding & DW_EH_PE_indirect != 0 {
            result = *(result as *const usize);
        }

        result
    }

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