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|
//! Parsing of GCC-style Language-Specific Data Area (LSDA)
//! For details see:
//! * <https://refspecs.linuxfoundation.org/LSB_3.0.0/LSB-PDA/LSB-PDA/ehframechpt.html>
//! * <https://itanium-cxx-abi.github.io/cxx-abi/exceptions.pdf>
//! * <https://www.airs.com/blog/archives/460>
//! * <https://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 super::DwarfReader;
use core::mem;
use core::ptr;
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<'a> {
pub ip: usize, // Current instruction pointer
pub func_start: usize, // Address of the current function
pub get_text_start: &'a dyn Fn() -> usize, // Get address of the code section
pub get_data_start: &'a dyn Fn() -> usize, // Get address of the data section
}
pub enum EHAction {
None,
Cleanup(usize),
Catch(usize),
Terminate,
}
pub const USING_SJLJ_EXCEPTIONS: bool = cfg!(all(target_os = "ios", target_arch = "arm"));
pub unsafe fn find_eh_action(lsda: *const u8, context: &EHContext<'_>) -> Result<EHAction, ()> {
if lsda.is_null() {
return Ok(EHAction::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.add(call_site_table_length as usize);
let ip = context.ip;
if !USING_SJLJ_EXCEPTIONS {
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_entry = 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 Ok(EHAction::None);
} else {
let lpad = lpad_base + cs_lpad;
return Ok(interpret_cs_action(action_table as *mut u8, cs_action_entry, lpad));
}
}
}
// Ip is not present in the table. This indicates a nounwind call.
Ok(EHAction::Terminate)
} else {
// SjLj version:
// The "IP" is an index into the call-site table, with two exceptions:
// -1 means 'no-action', and 0 means 'terminate'.
match ip as isize {
-1 => return Ok(EHAction::None),
0 => return Ok(EHAction::Terminate),
_ => (),
}
let mut idx = ip;
loop {
let cs_lpad = reader.read_uleb128();
let cs_action_entry = reader.read_uleb128();
idx -= 1;
if idx == 0 {
// Can never have null landing pad for sjlj -- that would have
// been indicated by a -1 call site index.
let lpad = (cs_lpad + 1) as usize;
return Ok(interpret_cs_action(action_table as *mut u8, cs_action_entry, lpad));
}
}
}
}
unsafe fn interpret_cs_action(
action_table: *mut u8,
cs_action_entry: u64,
lpad: usize,
) -> EHAction {
if cs_action_entry == 0 {
// If cs_action_entry is 0 then this is a cleanup (Drop::drop). We run these
// for both Rust panics and foreign exceptions.
EHAction::Cleanup(lpad)
} else {
// If lpad != 0 and cs_action_entry != 0, we have to check ttype_index.
// If ttype_index == 0 under the condition, we take cleanup action.
let action_record = (action_table as *mut u8).offset(cs_action_entry as isize - 1);
let mut action_reader = DwarfReader::new(action_record);
let ttype_index = action_reader.read_sleb128();
if ttype_index == 0 {
EHAction::Cleanup(lpad)
} else {
// Stop unwinding Rust panics at catch_unwind.
EHAction::Catch(lpad)
}
}
}
#[inline]
fn round_up(unrounded: usize, align: usize) -> Result<usize, ()> {
if align.is_power_of_two() { Ok((unrounded + align - 1) & !(align - 1)) } else { Err(()) }
}
unsafe fn read_encoded_pointer(
reader: &mut DwarfReader,
context: &EHContext<'_>,
encoding: u8,
) -> Result<usize, ()> {
if encoding == DW_EH_PE_omit {
return Err(());
}
// DW_EH_PE_aligned implies it's an absolute pointer value
if encoding == DW_EH_PE_aligned {
reader.ptr = reader.ptr.with_addr(round_up(reader.ptr.addr(), mem::size_of::<usize>())?);
return Ok(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,
_ => return Err(()),
};
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.expose_addr(),
DW_EH_PE_funcrel => {
if context.func_start == 0 {
return Err(());
}
context.func_start
}
DW_EH_PE_textrel => (*context.get_text_start)(),
DW_EH_PE_datarel => (*context.get_data_start)(),
_ => return Err(()),
};
if encoding & DW_EH_PE_indirect != 0 {
result = *ptr::from_exposed_addr::<usize>(result);
}
Ok(result)
}
|
