4b256ab968
When debug info was enabled, we would put the debug info sections in between the text section and the unwind info section. But the unwind info is encoded in a position-independent manner (so that we don't need relocs for it) that relies on it directly following the text section. The result of the misplacement was some crashes inside the unwinder.
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: *mut u8,
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unwind_info: *mut 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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