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//! Unwind info generation (`.eh_frame`)
use crate::prelude::*;
use cranelift_codegen::isa::{unwind::UnwindInfo, TargetIsa};
use gimli::write::{Address, CieId, EhFrame, FrameTable, Section};
use crate::backend::WriteDebugInfo;
pub(crate) struct UnwindContext<'tcx> {
tcx: TyCtxt<'tcx>,
frame_table: FrameTable,
cie_id: Option<CieId>,
}
impl<'tcx> UnwindContext<'tcx> {
pub(crate) fn new(tcx: TyCtxt<'tcx>, isa: &dyn TargetIsa) -> Self {
let mut frame_table = FrameTable::default();
let cie_id = if let Some(mut cie) = isa.create_systemv_cie() {
if isa.flags().is_pic() {
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 {
tcx,
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.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<P: WriteDebugInfo>(self, product: &mut P) {
let mut eh_frame = EhFrame::from(super::emit::WriterRelocate::new(super::target_endian(
self.tcx,
)));
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(feature = "jit")]
pub(crate) unsafe fn register_jit(
self,
jit_module: &cranelift_simplejit::SimpleJITModule,
) -> Option<UnwindRegistry> {
let mut eh_frame = EhFrame::from(super::emit::WriterRelocate::new(super::target_endian(
self.tcx,
)));
self.frame_table.write_eh_frame(&mut eh_frame).unwrap();
if eh_frame.0.writer.slice().is_empty() {
return None;
}
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]);
let mut registrations = Vec::new();
// =======================================================================
// Everything after this line up to the end of the file is loosly 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);
registrations.push(current as usize);
}
// 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
let ptr = eh_frame.as_ptr();
__register_frame(ptr);
registrations.push(ptr as usize);
}
Some(UnwindRegistry {
_frame_table: eh_frame,
registrations,
})
}
}
/// Represents a registry of function unwind information for System V ABI.
pub(crate) struct UnwindRegistry {
_frame_table: Vec<u8>,
registrations: Vec<usize>,
}
extern "C" {
// libunwind import
fn __register_frame(fde: *const u8);
fn __deregister_frame(fde: *const u8);
}
impl Drop for UnwindRegistry {
fn drop(&mut self) {
unsafe {
// libgcc stores the frame entries as a linked list in decreasing sort order
// based on the PC value of the registered entry.
//
// As we store the registrations in increasing order, it would be O(N^2) to
// deregister in that order.
//
// To ensure that we just pop off the first element in the list upon every
// deregistration, walk our list of registrations backwards.
for fde in self.registrations.iter().rev() {
__deregister_frame(*fde as *const _);
}
}
}
}
|
