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//! Unwind info generation (`.eh_frame`)
use cranelift_codegen::ir::Endianness;
use cranelift_codegen::isa::{unwind::UnwindInfo, TargetIsa};
use cranelift_object::ObjectProduct;
use gimli::write::{Address, CieId, EhFrame, FrameTable, Section};
use gimli::RunTimeEndian;
use super::object::WriteDebugInfo;
use crate::prelude::*;
pub(crate) struct UnwindContext {
endian: RunTimeEndian,
frame_table: FrameTable,
cie_id: Option<CieId>,
}
impl UnwindContext {
pub(crate) fn new(isa: &dyn TargetIsa, pic_eh_frame: bool) -> Self {
let endian = match isa.endianness() {
Endianness::Little => RunTimeEndian::Little,
Endianness::Big => RunTimeEndian::Big,
};
let mut frame_table = FrameTable::default();
let cie_id = if let Some(mut cie) = isa.create_systemv_cie() {
if pic_eh_frame {
cie.fde_address_encoding =
gimli::DwEhPe(gimli::DW_EH_PE_pcrel.0 | gimli::DW_EH_PE_sdata4.0);
}
Some(frame_table.add_cie(cie))
} else {
None
};
UnwindContext { endian, frame_table, cie_id }
}
pub(crate) fn add_function(&mut self, func_id: FuncId, context: &Context, isa: &dyn TargetIsa) {
let unwind_info = if let Some(unwind_info) =
context.compiled_code().unwrap().create_unwind_info(isa).unwrap()
{
unwind_info
} else {
return;
};
match unwind_info {
UnwindInfo::SystemV(unwind_info) => {
self.frame_table.add_fde(
self.cie_id.unwrap(),
unwind_info
.to_fde(Address::Symbol { symbol: func_id.as_u32() as usize, addend: 0 }),
);
}
UnwindInfo::WindowsX64(_) => {
// FIXME implement this
}
unwind_info => unimplemented!("{:?}", unwind_info),
}
}
pub(crate) fn emit(self, product: &mut ObjectProduct) {
let mut eh_frame = EhFrame::from(super::emit::WriterRelocate::new(self.endian));
self.frame_table.write_eh_frame(&mut eh_frame).unwrap();
if !eh_frame.0.writer.slice().is_empty() {
let id = eh_frame.id();
let section_id = product.add_debug_section(id, eh_frame.0.writer.into_vec());
let mut section_map = FxHashMap::default();
section_map.insert(id, section_id);
for reloc in &eh_frame.0.relocs {
product.add_debug_reloc(§ion_map, §ion_id, reloc);
}
}
}
#[cfg(all(feature = "jit", windows))]
pub(crate) unsafe fn register_jit(self, _jit_module: &cranelift_jit::JITModule) {}
#[cfg(all(feature = "jit", not(windows)))]
pub(crate) unsafe fn register_jit(self, jit_module: &cranelift_jit::JITModule) {
use std::mem::ManuallyDrop;
let mut eh_frame = EhFrame::from(super::emit::WriterRelocate::new(self.endian));
self.frame_table.write_eh_frame(&mut eh_frame).unwrap();
if eh_frame.0.writer.slice().is_empty() {
return;
}
let mut eh_frame = eh_frame.0.relocate_for_jit(jit_module);
// GCC expects a terminating "empty" length, so write a 0 length at the end of the table.
eh_frame.extend(&[0, 0, 0, 0]);
// FIXME support unregistering unwind tables once cranelift-jit supports deallocating
// individual functions
let eh_frame = ManuallyDrop::new(eh_frame);
// =======================================================================
// Everything after this line up to the end of the file is loosely based on
// https://github.com/bytecodealliance/wasmtime/blob/4471a82b0c540ff48960eca6757ccce5b1b5c3e4/crates/jit/src/unwind/systemv.rs
#[cfg(target_os = "macos")]
{
// On macOS, `__register_frame` takes a pointer to a single FDE
let start = eh_frame.as_ptr();
let end = start.add(eh_frame.len());
let mut current = start;
// Walk all of the entries in the frame table and register them
while current < end {
let len = std::ptr::read::<u32>(current as *const u32) as usize;
// Skip over the CIE
if current != start {
__register_frame(current);
}
// Move to the next table entry (+4 because the length itself is not inclusive)
current = current.add(len + 4);
}
}
#[cfg(not(target_os = "macos"))]
{
// On other platforms, `__register_frame` will walk the FDEs until an entry of length 0
__register_frame(eh_frame.as_ptr());
}
}
}
extern "C" {
// libunwind import
fn __register_frame(fde: *const u8);
}
|
