881c19473d
`ptr::cast` has the advantage of being unable to silently cast `*const T` to `*mut T`. This turned up several places that were performing such casts, which this PR also fixes.
93 lines
3.2 KiB
Rust
93 lines
3.2 KiB
Rust
//! Module for System V ABI unwind registry.
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use anyhow::Result;
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/// Represents a registration of function unwind information for System V ABI.
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pub struct UnwindRegistration {
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registrations: Vec<usize>,
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}
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extern "C" {
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// libunwind import
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fn __register_frame(fde: *const u8);
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fn __deregister_frame(fde: *const u8);
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}
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impl UnwindRegistration {
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/// Registers precompiled unwinding information with the system.
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///
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/// The `_base_address` field is ignored here (only used on other
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/// platforms), but the `unwind_info` and `unwind_len` parameters should
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/// describe an in-memory representation of a `.eh_frame` section. This is
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/// typically arranged for by the `wasmtime-obj` crate.
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pub unsafe fn new(
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_base_address: *const u8,
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unwind_info: *const u8,
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unwind_len: usize,
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) -> Result<UnwindRegistration> {
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debug_assert_eq!(
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unwind_info as usize % region::page::size(),
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0,
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"The unwind info must always be aligned to a page"
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);
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let mut registrations = Vec::new();
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if cfg!(any(
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all(target_os = "linux", target_env = "gnu"),
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target_os = "freebsd"
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)) {
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// On gnu (libgcc), `__register_frame` will walk the FDEs until an
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// entry of length 0
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__register_frame(unwind_info);
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registrations.push(unwind_info as usize);
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} else {
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// For libunwind, `__register_frame` takes a pointer to a single
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// FDE. Note that we subtract 4 from the length of unwind info since
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// wasmtime-encode .eh_frame sections always have a trailing 32-bit
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// zero for the platforms above.
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let start = unwind_info;
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let end = start.add(unwind_len - 4);
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let mut current = start;
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// Walk all of the entries in the frame table and register them
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while current < end {
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let len = std::ptr::read::<u32>(current as *const u32) as usize;
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// Skip over the CIE
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if current != start {
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__register_frame(current);
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registrations.push(current as usize);
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}
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// Move to the next table entry (+4 because the length itself is
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// not inclusive)
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current = current.add(len + 4);
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}
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}
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Ok(UnwindRegistration { registrations })
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}
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pub fn section_name() -> &'static str {
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".eh_frame"
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}
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}
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impl Drop for UnwindRegistration {
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fn drop(&mut self) {
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unsafe {
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// libgcc stores the frame entries as a linked list in decreasing
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// sort order based on the PC value of the registered entry.
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//
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// As we store the registrations in increasing order, it would be
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// O(N^2) to deregister in that order.
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//
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// To ensure that we just pop off the first element in the list upon
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// every deregistration, walk our list of registrations backwards.
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for fde in self.registrations.iter().rev() {
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__deregister_frame(*fde as *const _);
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}
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}
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}
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}
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